Nr4en2021

A JOURNAL OF MINING AND ENVIRONMENT

Vol. 27 Issue 4 / 2021 ISSN-L 1220-2053 / ISSN 2247-8590

Universitas Publishing Petroșani, Romania

REVISTA MINELOR - MINING REVUE A JOURNAL OF MINING AND ENVIRONMENT

Editorial board Editor in chief: Prof. Ilie ONICA Managing editors: Assoc.prof. Andrei ANDRAS Assoc.prof. Paul Dacian MARIAN Editorial advisory board: Prof. Dumitru FODOR Prof. Nicolae ILIAŞ Prof. Mircea GEORGESCU Prof. Pascu Mihai COLOJA Language editor: Lect. Lavinia HULEA Technical editor: Radu ION

ISSN-L 1220-2053 ISSN 2247-8590 www.upet.ro/revistaminelor www.sciendo.com/journal/MINRV

Scientific committee: Prof. Iosif ANDRAȘ, University of Petrosani, Romania PhD. Eng. Marwan AL HEIB, Ecole des mines de Nancy, INERIS, France Assist. prof. Adam BAJCAR, Poltegor-Instytut, Poland PhD. Eng. Iosif Horia BENDEA, Politechnico di Torino, Italy Assoc. prof. Boyko BEROV, Bulgarian Academy of Sciences, Bulgaria Prof. Essaid BILAL, Centre Sciences des Processus Industriels et Naturels (SPIN), France Prof. Lucian BOLUNDUȚ, University of Petrosani, Romania Prof. Ioan BUD, Technical University of Cluj-Napoca (North Center of Baia Mare), Romania Prof. Nam BUI, Hanoi University of Science and Technology, Vietnam PhD. Eng. Constantin Sorin BURIAN, INSEMEX Petrosani, Romania Prof. Eugen COZMA, University of Petrosani, Romania PhD. Eng. György DEÁK, National Institute for Research and Development in Environmental Protection Prof. Nicolae DIMA, University of Petrosani, Romania Prof. Carsten DREBENSTEDT, TU Bergakademie Freiberg, Germany Prof. Ioan DUMITRESCU, University of Petrosani, Romania PhD. Eng. George-Artur GĂMAN, INSEMEX Petrosani, Romania Prof. Ioan GÂF-DEAC, Dimitrie Cantemir Christian University Bucharest, Romania Ph.D. Eng. Edmond GOSKOLLI, National Agency of Natural Resources, Albania Prof. Andreea IONICĂ, University of Petrosani, Romania Prof. Sair KAHRAMAN, Hacettepe University, Turkey Prof. Sanda KRAUSZ, University of Petrosani, Romania Prof. Krzysztof KOTWICA, AGH University of Science and Technology Krakow, Poland Prof. Maria LAZAR, University of Petrosani, Romania Prof. Monica LEBA, University of Petrosani, Romania Prof. Roland MORARU, University of Petrosani, Romania PhD. Eng. Vlad Mihai PĂSCULESCU, INSEMEX Petrosani, Romania Prof. Sorin Mihai RADU, University of Petrosani, Romania Prof. Ilie ROTUNJANU, University of Petrosani, Romania Prof. Mihaela TODERAȘ, University of Petrosani, Romania Assoc. prof. Sorin Silviu UDUBAȘA, University of Bucharest, Romania Prof. Ioel VEREȘ, Technical University of Cluj-Napoca, Romania Assoc. prof. Zoltan Istvan VIRÁG, University of Miskolc, Hungary

© Copyright by UNIVERSITAS Publishing House Petroşani / Revista Minelor - Mining Revue published quarterly Editorial contact: Ilie ONICA, e-mail: onicai2004@yahoo.com, phone: 0040 729 066 723 Dacian-Paul MARIAN, e-mail: dacianmarian@upet.ro, phone: 0040 748 130 633 University of Petroşani, 20 Universităţii str., 332006 Petroşani, Romania Phone +40254 / 542.580, fax. +40254 / 543.491 Printed by University of Petroşani Printing Department

Vol. 4 / 2021 ISSN-L 1220-2053 / ISSN 2247-8590

UNIVERSITAS PUBLISHING Petroșani, Romania

CONTENTS

Eva BIRO, Sorin Mihai RADU, Doru CIOCLEA, Ion GHERGHE Restructuring simulation of the ventilation network

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Florin FAUR, Maria LAZĂR, Ciprian DANCIU, Izabela-Maria APOSTU Investigations on the stability of the right slope in the area of Anina wastewater treatment plant

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Dacian-Paul MARIAN, Ilie ONICA Improving the stability of the directional room G 31-33, Horizon 210 - East, Ocnele Mari – Cocenești Salt Mine, by reinforcement with anchors and shotcrete

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Zoltán VIRÁG, Sándor SZIRBIK Analysis of a replaceable cutting tooth of bucket chain excavator

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Ildiko BRÎNAȘ Simulation of the vibrations produced to the human body during operation of the bucket wheel excavators. A case study of ERc 1400-30/7 type excavator

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Andrei ANDRAȘ, Florin Dumitru POPESCU Romanian carbonate rocks cuttability assessment using linear cutting tester

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Liliana ROMAN Considerations regarding the closure of the mines in Valea Jiului

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Nurudeen SALAHUDEEN, Ahmad A. MUKHTAR Effect of beneficiation on the characterization of Getso kaolin

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Nurudeen SALAHUDEEN, Aminat Oluwafisayo ABODUNRIN Mineralogical, physicochemical and morphological characterization of Okpella clay

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RESTRUCTURING SIMULATION OF THE VENTILATION NETWORK Eva BIRO1, Sorin Mihai RADU2*, Doru CIOCLEA3. Ion GHERGHE4 INCD INSEMEX Petroșani, Romania University of Petroșani, Romania, sorinradu@upet.ro 3 INCD INSEMEX Petroșani, Romania 4 INCD INSEMEX Petroșani, Romania 1

2

DOI: 10.2478/minrv-2021-0029 Keywords: simulation, ventilation, coal extraction, mining, restructuring Abstract: Worldwide, the demand for raw materials and materials is constantly increasing, being proportional to the growth of the population. In this sense, the demand and production of solid fuels such as coal has grown steadily. At the level of the European Union, due to the restrictive coal extraction policy, production has steadily decreased and coal-producing countries have had to implement closure programs with strict deadlines. As mining networks shrink, there is an intensification of risk factors due to changes in the ventilation system. The paper presents the restructuring of a complex ventilation network.

1. Introduction The exploitation of superior coals underground implies the successive execution of a complex of mining works for opening, preparation and exploitation [1, 2]. As the operation expands both horizontally and vertically, some mining works are closed and others are carried out in such a way that they can put major problems in terms of ventilation. Complex ventilation networks involve the presence of parallel, diagonal and complex diagonal connections that can generate relatively low total aerodynamic resistance. Given that it is necessary to restrict the ventilation network, the number of parallel connections is reduced proportionally, which inevitably leads to the appearance of high total aerodynamic resistances. This aspect put special problems for ventilation specialists because main ventilation stations, horizons or operating blocks can be removed from the ventilation network. [3, 4, 5, 6, 7].

2. Reason for restructuring the ventilation network The analyzed network is that of the Livezeni Mine which is extended horizontally [8]. In this sense there are two distinct areas connected by the directional coal and sterile galleries. The two distinct areas are: - The western area located around layer 13 and which is opened by skip and auxiliary wells. The ventilation network in this area is sectorized and in this sense this area has the East ventilation Shaft which has to the surface the main ventilation Station East Shaft; - The eastern area located around layer 3 and which is opened by the auxiliary shaft no. 3 of fresh air inlet.

The ventilation network in this area is sectorized and in this sense this area has the ventilation shaft no. 2 which has to the surface the main ventilation Station ventilation shaft nr. 2; The ventilation network also includes underground mining located on four horizons (horizon 100; horizon 300; horizon 350; and horizon 475). These works consist of main transverse galleries, directional galleries, diagonal galleries, transverse number galleries, inclined planes, work fronts, connecting risings.

Due to economic constraints as well as for security reasons, the decision to restrict the ventilation network can be taken. Given the difficulties of continuing to operate Layer 3, due to the spontaneous combustion phenomena that led to the closure of production capacity, the decision could be taken to continue operating

*

Corresponding author: Radu Sorin Mihai, prof. Ph.D. eng., University of Petrosani, Petrosani, Romania, (University of Petrosani, 20 University Street, sorin_mihai_radu@yahoo.com) 1

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Layer 13. In this regard, the entire eastern area could be closed and the main ventilation station Auxiliary shaft no. 2, can to be stopped.

In this new situation the structure of the ventilation network can be simulated on the ventilation network modeled and solved in the current conditions [9, 10, 11, 12, 13].

The specialized program used for the expected simulation is VENTSIM Visual Advanced [14].

3. Presentation of the VENTSIM program Ventsim Visual Advanced is a specialized program and a very good tool for analyzing the solution and simulation of complex ventilation networks [14].

This program allows both the modeling, solving and simulation of a ventilation network and its analysis in order to optimize it. The program itself provides both information on network-specific aerodynamic parameters and information on ventilation costs.

4. Simulation of the ventilation system of Livezeni Mine The simulation of the mine ventilation network was performed on the ventilation network modeled and solved in the current conditions fig. 1, [15, 16, 17, 18, 19, 20, 21].

Figure 1. 3D ventilation network of the Livezeni Mine The simulation of the restructuring of the Livezeni mine ventilation network required the elimination of the following mining works:- Coal main gallery, horizon 300; - Sterile main gallery, horizon 300; - Conection gallery to incline plan for conveyor - The connection galleries of the main galleries; belts; - Panel 4N, horizon 300; - Incline plan for conveyor belts; - Transport incline plan Panel 5N; - Stanca ventilation incline plan; - Connection rising to the transport incline plan; - Ventilation rising Panel 6; - Silo no. 2; - Connection incline plan Silo no. 15; - Inclined plane for conveyor belts; - Silo no. 15; - Silo access incline plan no. 8; - Transformation station no. 102; - Silo no. 8; - Valache ventilation incline plan; - Silo no. 9; - Transversal gallery horizon 350; - Connection gallery to Silo no. 9; - Auxiliary shaft Circuit no. 3, horizon 350; - 4N panel ventilation plan; - Degertu rising; 2

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- Access gallery to Degeratu rising; - Transversal gallery horizon 475; - Auxiliary shaft Circuit no. 3, horizon 475; - Auxiliary shaft no. 3; - Delta horizon 475;

- Directional gallery horizon 475; - Transformation station horizon 475; - Ventilation circuit shaft no. 2 horizon 475, - Ventilation shaft no. 2; - Ventilation channel shaft no. 2;

Figure 2 shows the simulation of the ventilation network under the conditions of restructuring in the western area.

Figure 2. Simulated ventilation network after restructuring As a result of the restructuring of the ventilation network, a number of 84 junctions and 112 connections remained.

Figures 3. - 12. show details of the ventilation network as follows: the central area Auxiliary Well - Skip shaft; Auxiliary shaft - Skip Circuit area; Detail area Puț Orb no. 6, 300-100; Detail of the Inclined Plan area, 300-100; Detail Circuit Blind shaft no. 6, horizon 100; area layer 13 oriz. 100; Detail of Hausser's rising; East Ventilation shaft Area; Detail Main ventilation station East shaft.

Figure 3. Skip and auxiliary well area

Figure 4. Central area horizon 300

Figure 5. Auxiliary Well - Skip Well circuit area

Figure 6. Blind Well no. 6, 300-100

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Figure 7. Inclined plane 300-100

Figure 8. Blind Well no. 6 Circuit, horizon 100

Figure 9. Layer 13 area, horizon 100

Figure 10. Hausser rising

Figure 11. East Ventilation Well Area

Figure 12. East Main ventilation Station

The results obtained following the simulation and solving of the ventilation network related to the restructured Livezeni mine, are presented in figure 13 for the topographic coordinates respectively in figure 14 for aerodynamic parameters.

Figure 13 Topographic coordinates

Figure 14 Aerodynamic parameters

In order to solve the ventilation network in the conditions of restriction and limitation to the western area, the following have been eliminated: - 4 ventilation doors in the circuit area Skip shaft - Auxiliary shaft, horizon 300; - 4 ventilation doors from the Blind shaft no. 6 area, horizon 300: 4

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The aerodynamic resistance on the following mining works has also been modified: - Inclined plane collector horizon 300-100; - Iscroni directional Gallery, horizon 300.

Following the solution of the simulated ventilation network, the following data resulted: • A fresh air flow of 23.8 m3/s or 1428 m3/min was introduced underground, distributed as follows: - Auxiliary shaft: 16.8 m3/s or 1008 m3/min; - Skip shaft: 7.0 m3/s or 420 m3/min; TOTAL ENTRY: 23.8 m3/s or 1428 m3/min.

• 6.1 m3/s or 366 m3/min were obtained on the Iscroni main gallery; • The air flow at the level of the blind shaft no. 6 was 10.1 m3/s or 606 m3/min; • At the level of the main gallery oriz. 100 was obtained 10.1 m3/s or 606 m3/min; • At the level of the 300-100 collector inclined plane, 7.7 m3/s or 462 m3/min was obtained; • On the conjugated directional galleries west, horizon 100, 14.4 m3/s or 864 m3/min was obtained; • On the inclined plane of ventilation no. 15 was obtained 17.8 m3/s or 1068 m3/min; • On the East Ventilation Well, from the underground was evacuated at mine level, a defective air flow of 23.8 m3/s or 1428 m3/min; • 32 m3/s or 1920 m3/min were evacuated at the level of the East Main Ventilation Station; • The short-cut air flow with the surface was 8.2 m3/s or 492 m3/min.

5. Conclusions The specialized program Ventsim Visual Advanced was used to simulate the ventilation network, under restructuring conditions, of the Livezeni mine.

As a result of performing the simulation in solid 3D system, a number of 84 junctions and 112 connections resulted.

Ventsim Visual Advanced is a specialized program and a very good tool for analyzing the solution and simulation of complex ventilation networks To simulate the ventilation network of the Livezeni mine, 34 ventilation circuits or mining works were eliminated. Also, 8 ventilation doors were eliminated and at the level of 2 other ventilation doors the aerodynamic resistances were modified.

From the underground, the air flow at the mine level of 23.8 m3/s or 1428 m3/min was evacuated from the underground; At the level of the main fan, 32.0 m3/s or 1920 m3/min. was evacuated.

The short-cut air flow with the surface was 8.2 m3/s or 492 m3/min.

References [1] Almăşan B., 1984 The exploitation of mineral deposits in România (in Romanian), Technical Publishing București [2] Covaci Ş., 1983 Underground mining (in Romanian), Didactic and Pedagogic Publishing București [3] Băltăreţu R., Teodorescu C., 1971 Mining ventilation and work protection (in Romanian), Didactic and Pedagogic Publishing București [4] Matei I., Moraru R, e.a., 2000 Environmental engineering and underground ventilation Technical Publishing București [5] Patterson A.M., 1992 The Mine Ventilation Practitioner’s Data Book, M.V.S. of South Africa [6] Todorescu C., Gontean Z., Neag I., 1971 Mining ventilation (in Romanian), Technical Publishing București [7] * * *, 1990 Le Roux - Notes on Mine environmental control, M.V.S. of South Africa

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[8] * * *, 2021 Technical documentation, Livezeni Mining Unit [9] Boantă C., 2019 The management of the ventilation complex network of Vulcan Mine from the Valea Jiului mining area and the establishment of gas dynamics (in Romanian), Doctoral thesis, University of Petrosani [10] Chiuzan E., 2019 The management of the ventilation network from Praid Salt Mine (in Romanian), Doctoral thesis, University of Petrosani [11] Morar M.S., 2016 Research on the improvement of the ventilation networks management from the mining exploitations in Valea Jiului (in Romanian), Doctoral thesis, University of Petrosani [12] Rădoi F., 2018 The optimization of ventilation networks from the Valea Jiului’s closing mines, for the increase of work safety (in Romanian), Doctoral thesis, University of Petrosani [13] Șuvar M., 2017 Research on the restauration of the mining ventilation networks after explosions (in Romanian), Doctoral thesis, University of Petrosani [14] * * *, 2010 VENTSIM Visual Advanced – User’s Guide [15] Cioclea D., 2006 Solving the ventilation network problems on depressiometric measurements in order to establish the air flows, depressions and aerodynamic resistances on works from E.M. Paroșeni (in Romanian), INSEMEX research.

[16] Cioclea D., 2007-2009 Reducing the risks generated by explosives by using the real-time evaluation technique of the ventilation networks for human protection (in Romanian), INSEMEX research.

[17] Cioclea D., 2010-2011 Reducing the explosion danger for the black coal mines in Valea Jiului through the computer management of the ventilation networks (in Romanian), INSEMEX research.

[18] Gherghe I., 1998 Determining the characteristic curves of the main ventilation fans from E.M. Livezeni (in Romanian), INSEMEX research.

[19] Ianc N., 2018 Curved determinations characteristic for the main ventilation installations Puț Aeraj 2 and Puț Aeraj East – E.M. Livezeni (in Romanian), INSEMEX research.

[20] Matei A., 2014 The determination of the characteristic curves of fans and of the functional parameters from the main ventilation stations – Puț East and Puț Aeraj 2 from E.M. Livezeni (in Romanian), INSEMEX research.

[21] Rădoi F., 2015 The determination of characteristic curves of the fans and of the functional parameters from the main ventilation installation Puț Aeraj 2, on the inclination angle value of the rotor blades of α = 15°, from E.M. Livezeni, (in Romanian), INSEMEX research.

This article is an open access article distributed under the Creative Commons BY SA 4.0 license. Authors retain all copyrights and agree to the terms of the above-mentioned CC BY SA 4.0 license.

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INVESTIGATIONS ON THE STABILITY OF THE RIGHT SLOPE IN THE AREA OF ANINA WASTEWATER TREATMENT PLANT Florin FAUR1, Maria LAZĂR2, Ciprian DANCIU3. Izabela-Maria APOSTU4* 1

University of Petrosani, Faculty of Mining, Department of Environmental Engineering and Geology, Petrosani, Romania, florinfaur@upet.ro 2 University of Petrosani, Faculty of Mining, Department of Environmental Engineering and Geology, Petrosani, Romania, marialazar@upet.ro 3 University of Petrosani, Faculty of Mining, Department of Mining Engineering, Surveying and Constructions, Petrosani, Romania, cipriandanciu@upet.ro 4 University of Petrosani, Faculty of Mining, Department of Environmental Engineering and Geology, Petrosani, Romania, izabelaapostu@upet.ro

DOI: 10.2478/minrv-2021-0030 Keywords: consequent slide, stability, polygonal surface, right slope Abstract: Often, excavations of natural slopes are necessary in the site area for the construction of civil or industrial objectives. The execution of such works requires special attention, from the design phase, regarding the stability of the slope in the initial state, but also after excavation and identification, if necessary, of technical solutions to increase the stability reserve, thus ensuring the security during the execution of works but also of future constructions. Such a situation was encountered in the case of Anina Wastewater Treatment Plant (WWTP), when, in the absence of proper investigations of the slope to be excavated, there was a landslide that interrupted the site activities, and which, to some extent, jeopardized the objectives already built. In this context, at the level of 2015, slope stabilization works were designed and executed, works that proved to be insufficient. In 2021, it was necessary to conduct a new stability study in order to analyze the possibilities of continuing the construction of the treatment plant. This paper presents the results obtained during this study, as well as a series of conclusions and interpretations, regarding the technical condition of the slope in different hypotheses.

1. Introduction The town of Anina is located in Anina Mountains, that represent the southern extension of Western Carpathians, in Romanian Banat, having the coordinates 45°2'30 "north latitude and 21°53'20" east longitude, in Caraş-Severin county. The average altitude of the settlement is +645 m and the minimum is +556 m and is located near the railway station [1] (Figure 1).

The town of Anina is located about 32 km, on DN 58, from Reșita Municipality, the residence and administrative center of the county, at 33 km, on DN 57B, from Oraviţa and at 34 km, on DN 57B, from Bozovici towns.

Anina WWTP site is approx. 1.2 km, on a NNE direction from Anina town, on the right bank of Gârliste River, inside Semenic Cheile Carașului National Park (Figure 1).

The main objective of this study was to investigate the technical condition (stability) of the right slope in WWTP Anina area (Gârliștei valley), and as a secondary objective to establish some recommendations on the possibility of carrying out excavation works, allowing the location of 4 premises (A1, A2, A8 and A11 according to the construction plan of WWTP Anina [2]).

We specify the fact that the investigated area was affected by a landslide (Figure 2), in 2015, subsequently being designed and executed land stabilization works, the technical solution being represented by a fixing system with metal nets and anchors [3].

*

Corresponding author: Apostu Izabela-Maria, Assist.prof.dr.eng., University of Petrosani, Petrosani, Romania, (University of Petrosani, University Street no. 20, izabelaapostu@upet.ro) 7

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Area affected by the 2015 landslide

Figure 1. Location of the studied area

a b Figure 2. The landslide: a - in 2015 [3], immediately after the event; b - in 2021, relatively stabilized

Also in that period, a second variant of securing the slope was considered, namely with the help of retaining walls, in this sense being considered two technical solutions [4].

During the field investigations, it was found that part of the system consisting of metal nets and anchors gave way (Figure 3), requiring another solution to stabilize the slope.

Figure 3. Damage to metal nets and anchors

We specify that the initial landslide occurred during the execution of excavation works at the base of the slope, allowing the location of the 4 enclosures mentioned, and was described as a consequent landslide (sliding surface inclining in the same direction as the stratification of the slope) on a slope of approx. 30°. The slide involved the movement of strongly altered sandstone blocks (especially physically: affected by massive cracks, developed both vertically and horizontally) and was favored by the presence of clays and water from precipitation [3] (Figure 4a).

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The sliding process involved the movement of large blocks of rock (20 - 40 t, and over 2 m high), had a surface development of approx. 15 - 20 m and manifested itself at a depth of approx. 7 m (Figure 4b). The body of the landslide was composed of an uneven mixture of massive blocks of altered and unaltered rocks with clay intercalations with moist content [1].

a b c Figure 4. Stratigraphic aspects: a - the consequent inclination of the rock layers with that of the slope; b - the appearance of the rock blocks involved in the landslide from 2015; c - schistosity of slipped blocks

There is also the schistosity that characterizes the blocks involved in the landslide (Figure 4c) but also those left in place, and which in turn can have a significant influence in triggering a new landslide or in reactivating the one in 2015. This schistosity can have implications and in choosing a future slope stabilization solution.

2. Considerations regarding the geology of the massif, hydrology and climate 2.1. Geology Anina Mountains area is part of the mountainous and hilly unit developed on the alpine orogeny of Western Carpathians, Banat Mountains group, a subdivision of plateaus and limestone mountains within Reșita - Moldova Nouă syncline. This subdivision forms the middle region of Banat Mountains, in which the karst relief predominates. Anina Mountains have characteristic geomorphological features, as a consequence of their geological composition. The predominant rock is limestone arranged in synclines and anticlines with a NNVSSE direction, and the relief, adapted to the structure, consists of ridges and parallel valleys inscribed in the direction of the geological structure, and of extensive limestone plateaus "sifted" by sinkholes. To the east and north, sandstones and conglomerates appear in the Anina Mountains [1].

Due to the differentiated erosion, exerted on rocks with different hardness, as well as the tectonics, local depressions were born: Caraşova, Lişava, Ciudanoviţa, Anina etc.

The deposits on which the perimeter of the construction site is located are of Lower Permian, Lower Jurassic, Middle Jurassic and Holocene age [5]: Lower Permian is represented at the base of the formation by black shale clays. Superior, it is progressively switched to red sandstones and clays with intercalations of conglomerates and red-purple archaic sandstones with green spots. On the edges of the sedimentation zone, the red horizon is arranged directly on Stephanian conglomerates or even on the crystalline.

Lower Jurassic begins with Lower Liassic, which presents in the basal part a coarse conglomerate, formed almost exclusively of quartz elements and crystalline schist, with siliceous cement. Over the basal conglomerates from Anina, there is an alternation of micaceous sandstones, clayey sandstones, coal shale, coal and refractory clays, with a thickness of approx. 250 m. The Middle and the Upper Liassic are represented by a pelitic series, clayey-shale, a package called "bituminous shale horizon". Having a thickness of approx. 200 m, this horizon consists predominantly of black schist that at the top gradually pass to the sandy gray clays where spherosiderite concretions are found.

Middle Jurassic is represented by Aalian-Callovian and is transgressive. Aalian and Bajocian are composed of gray or yellowish sandy marls with frequent Leioceras molds. Bathonian is generally marlycalcareous and frequently contains lamelibmanchiats. Callovian continues the marly-calcareous facies, being characterized by the presence of sandstone-calcareous ellipsoidal concretions.

Holocene is represented by an alternation of rolled gravels, sands and meadow dust. These are also common on the banks of various valleys.

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Analyzing the available documentation, we found that the three geotechnical studies conducted in May 2011, May 2015 and October 2015 identify differently the type of rocks that make up the massif: - the study from May 2011 - conglomerates [5]; - the study from May 2015 - strongly altered sandstones [4]; - the study from October 2015 - limestone marls (with the aspect of weak sandstones) [1].

For this reason, on the samples taken from the drillings executed in 2021, new laboratory investigations were performed in order to correctly identify the rocks in the slope structure (Table 1).

0 – 0.20 m 0.20 – 2.37 m

2.37 – 2.65 m 2.65 – 10.00 m

Table 1. Stratigraphy of the slope F1 Drilling Clay, carbonaceous clay 0 – 1.80 m Limestone marls with sandstone appearance (fragmented) Limestone marls (with limestone fragments) Limestone marls with sandstone appearance (massive) RQD = 80.55%

1.80 – 2.00 m 2.00 – 2.30 m 2.30 – 4.00 m 4.00 – 5.00 m 5.00 – 10.00 m

F3 Drilling Missing - unrecovered Fragments of carbonaceous clay, bituminous clay Marl fragments, limestone marls Limestone marls with sandstone appearance Limestone, limestone fragments, dolomite limestone Limestone marls RQD = 50.20%

The research team from the University of Petroșani (UP) came to the conclusion that the slope is made up of a succession of strata (having as reference the F1 drilling, considered to be, by positioning relative to the investigated area of the slope, representative) (Figure 5): - at the top, a shallow layer of topsoil followed by a mixture of skeletal clays, sometimes with carbonaceous clays (difficult to separate, which is why subsequent investigations were carried out considering the whole mixture) (A layer); - a layer of limestone marls with the aspect of sandstone, strongly cracked (fragmented) (M1 layer); - a layer (intercalation) of limestone marl (I layer); - a basic layer (relative to the depth of the geotechnical drilling) of massive limestone marls with the aspect of sandstone (not affected by cracks) (M2 layer).

Figure 5. F1 and F3 drillings

From this point of view, the conclusions of the research team within UP are very close to those contained in the October 2015 study, noting that the I layer, that separates the two layers M1 and M2 (the strongly cracked and the massive one), is clearly highlighted.

What the three previous studies and the current one have in common is the fact that all of them (although they identify different types of rocks) highlight the high degree of fragmentation (cracking) of the M1 layer.

From a petrographic point of view, we are dealing with sedimentary rocks in transition between precipitation carbonate rock (myocritical limestone) mixed with clayey (siltic) terrigenous material [1].

The rocks in layers M1 and M2 are hard and compact (but cracked in the first layer and massive in the second). For the M1 layer, supergene and superficial alterations are observed. Also, in the composition of the analyzed samples were observed fine sequins of muscovite and diaclases with calcite (less than 5 mm thick) [1].

2.2. Hydrology and climate Anina town is crossed by Gârliște river which is part of the larger Caraş river basin, being allocated to the area with rich humidity, namely to the group with strongly drained groundwater.

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Groundwater areas in crystalline rocks and intrusive rocks are distinguished by rich resources, located in the fissures of these rocks. In the upper deluvial layer, relatively large variations of the amounts of groundwater resources are characteristic, which is also reflected in the underground river supply regime, thus prolonging the period of high waters and the duration of floods [5].

Waters formed under such conditions are generally poorly mineralized (usually 50-200 mg/l) and belong to the carbonated water class. In depression areas or low terraces and meadows, the groundwater level can have relatively shallow depths, from -1 m to -10 m.

From a meteorological point of view, the territory of Anina falls within the moderate continental climate sector, with the following characteristics [1, 5]: - average annual temperature: +10.5°C; - July average (warmest): +21°C; - January average (coldest): -0.8°C; - average amount of precipitation: 1200-1400 mm/year; - frost depth: 100 cm; - number of days with frost: 106 days/year; - average duration of the frost-free interval: 250; - wind direction: E: 13.7%; N: 12.4%; NW: 11.5%, (62.4% calm).

3. Slope stability investigations 3.1. Establishing the hypotheses of landslides occurrence After analyzing the structure of the investigated slope and based on the experience gained over the years by members of the research team, it was concluded that landslides can occur only at the contact surface between the constituent layers (these are usually areas of minimum strength, especially in the case of slopes made up of inclined strata, consequent with the slope of the terrain).

Thus, two generic surfaces on which the sliding surfaces can materialize were considered: - the first (most likely and analyzed in detail) at the contact between layers A and M1 (the strongly fragmented one); - the second (for which assessments were made on the basis of previous studies presented in the literature) at the contact between the I layer and the M1 layer.

3.2. Physical and geomechanical characteristics of the rocks In order to perform stability analyzes, the next important step is to rigorously determine the physical and mechanical characteristics that characterize the rocks in the slope structure.

Thus, starting from the hypotheses of landslides occurrence considered in this study, determinations were made for each type of rocks encountered in drilling and for the contact surfaces between them (Figure 6), the results being presented in Tables 2 - 8.

a b c d Figure 6. Determining the geomechanical characteristics: a - sheared specimens according to a mandatory plan; b - limestone marls samples (inclusion) in the shear boxes (in natural and saturated state); c - test specimens subjected to traction (Brazilian method); d - specimens subjected to uniaxial compression Crt. No. 1.

2.

3.

4.

Table 2. Physical characteristics of some rocks from the slope structure Apparent density Rock name/Collection place/State of the specimen (volumetric), ρa [kg/m3] Layer A/Superior strata/Natural moisture 1.802 Layer A/ Superior strata /Saturation 1.993 Layer I/Inclusion/Natural moisture 2.341 Layer I/Inclusion/Saturation 2.493 11

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Table 3. Apparent density (volumetric) of rocks from M1 and M2 layers Apparent density (volumetric), ρa Crt. Rock name/Collection place/State [kg/m3] No. of the specimen On sample Average 1.

2.652 2.

2.649 3.

2.645 Layer M1/Anina/Natural moisture 2.649 4.

2.642 5.

2.649 6.

2.659 Table 4. Shearing resistance for specimens tested according to a mandatory plan (layer M1) Mechanical characteristic Shearing resistance (mandatory plan) Crt. Rock name/Collection α = 30º No. place/State of the specimen σ [MPa] τ [MPa] On sample Average On sample Average 1.

16.96 9.79 2.

16.30 9.41 3.

17.54 10.13 Layer M1/Anina/ 16.94 9.78 Natural moisture 4.

17.77 10.26 5.

15.77 9.10 6.

17.32 10.00

Crt. No. 1.

2.

3.

4.

5.

6.

Table 5. Determining the cohesion and internal friction angle (layer M1) by shearing Mechanical characteristic Rock Internal Shearing resistance (mandatory plan) name/Collection Cohesion friction α = 60º place/State of the c [MPa] angle σ [MPa] τ [MPa] specimen φ [°] On sample Average On sample Average 4.49 7.77 3.62 6.28 3.24 5.62 Layer M1/Anina/ 3.78 6.55 5.62 14.35 Natural moisture 3.34 5.79 4.06 7.03 3.94 6.82

Table 6. Determining the cohesion and internal friction angle (layer M1) by uniaxial compression and traction Mechanical characteristic Rock Resistance to uniaxial Resistance to traction Internal Crt. name/Collection compression, (Brazilian method), Cohesion friction No. place/State of the σrc [MPa] σrt [MPa] c [MPa] angle specimen On sample Average On sample Average φ [°] 1.

27.14 10.36 2.

29.14 11.79 3.

28.67 9.98 Layer M1/Anina/ 28.38 10.12 8.47 28.31 Natural moisture 4.

29.59 9.05 5.

28.19 9.43 6.

27.56 9.14 Table 7. Determining the cohesion and internal friction angle at the contact between layers I și M1 Mechanical characteristic Shearing resistance (direct) Rock name/Collection Internal Crt. Cohesion place/State of the On the contact surface friction angle 2 No. c [daN/cm ] specimen φ [°] σ [daN/cm2] τ [daN/cm2] On sample On sample 1.

1.75 4.86 I- M1/Anina/Natural 2.72 31.84 moisture 2.

2.25 5.28 3.

1.75 2.36 I- M1/Anina/Saturated 0.91 27.47 4.

2.25 2.71 12

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Table 8. Determining the cohesion and internal friction angle at the contact between layers A and M1 Crt. Cohesion Internal friction angle Rock name/Collection place/State of the specimen No. c [daN/cm2] φ [°] 1.

A – M1/Anina/Natural moisture 0.38 21.13 2.

A – M1/Anina/Saturated 0.23 19.02

Analyzing tables 2 - 8, it can be see that, although the individual mechanical characteristics are some that could suggest that we are dealing with a more stable slope, if we focus on these characteristics in the case of contact surfaces between different layers of rocks, they are relatively low (especially at the contact of layers A and M1), and thus, under certain conditions, can lead to landslides that can involve significant volumes of rocks.

3.3. Modeling the slope stratigraphy For modeling the slope stratigraphy, beyond the drilling performed in 2021, we took a series of information from previous geotechnical studies (especially geophysical investigations contained in the study conducted in May 2015 [3, 4] - Figure 7a), and for modeling the current geometry of the slope we considered the topographic profiles made in 2021.

Figure 7b shows the geometry and stratigraphy of the slope, as modeled using the stability analysis software.

a

b Figure 7. The geometry and stratigraphy of the slope: a – geophysical profile [1, 9]; b – model in Slide software 13

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3.4. Performing stability analyzes Two specialized software (Slide and GeoTecB) were used to perform the actual stability analyzes, which allow the definition of generic sliding surfaces at the contact between the layers that make up the slope.

Hypothesis 1 - slide occurs at the contact surface between layers A and M1 (strongly fragmented).

The analyzes were performed taking into account, progressively, a series of factors that influence (negatively) the stability reserve of a slope (conditions of saturation of the constituent rocks and the hypothesis of earthquakes), so that some considerations can be performed on the appropriateness of resuming the excavations at the base of the slope to ensure the necessary space for the construction of premises A1, A2, A8 and A11 (according to the construction plan of WWTP Anina [2]).

The initial stability analyzes are presented in figure 8a – d (performed with Slide software). We specify that the analyzes were performed by several procedures (Fellenius, Bishop, Janbu, Morgenstern-Price), well known and recommended by the literature [6, 7, 8, 9]), in this paper being illustrated the situations for which the most unfavorable values were obtained (the lowest safety coefficients for each situation).

a

b

c

d

e f Figure 8. Stability analyzes: a - natural moisture of the contact area between the layers; b - natural moisture of the contact area between the layers considering the influence of a seismic shock with an acceleration of 0.25g; c - saturation of the contact area between the layers; d - saturation of the contact area between the layers and under the influence of a seismic shock with the acceleration of 0.25g; e - saturation of the contact area between the layers and under the influence of a seismic shock with the acceleration of 0.25g; f - saturation of the contact area between the layers and of the upper clay layer and under the influence of a seismic shock with the acceleration of 0,25g 14

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In order to validate the most unfavorable result, obtained taking into account the saturation of the contact area and the production of a seismic shock simultaneously with the development of excavation and/or construction activities on site, we doubled this analysis by using a second geotechnical software (GeoTecB) (Figure 8e).

A last analyzed situation considers not only the saturation of the contact area, but also of the clay layer located in the upper part of the slope. This possibility is shown in Figure 8f.

We also specify that in order to study the possible influence of seismic shocks on stability, in the analyzes we considered a seismic acceleration of 0.20g (corresponding to the seismic zoning map of the Romanian territory contained in P 100-1 Design Code [10]), in which we added an acceleration of 0.05g, given by the vibrations transmitted by the machines to the slope in the hypothesis of resuming the excavation and construction activities.

In order to synthesize the results of the stability analyzes performed within the first hypothesis of producing a landslide, on a surface materialized at the contact between layers A and M1, we built table 9.

Crt. No. 1.

2.

3.

4.

5.

6.

Sliding surface

Polygonal, at the contact between layers A și M1

Table 9. Results of the stability analyses Analyses Conditions and influence factors method Natural moisture Janbu Natural moisture + seismic shock Janbu Saturation Janbu Saturation + seismic shock Janbu Saturation + seismic shock Fellenius Saturation + saturated clays + seismic Fellenius shock

Safety coefficient 2.525 1.409 1.750 0.994 0.960 0.900

Software Slide Slide Slide Slide GeoTecB GeoTecB

Analyzing those presented in Figure 8 and Table 9 we can draw the following conclusions: - in conditions of natural moisture (by which we mean the humidity at a given time of the rocks in the slope, in this case at the time of sampling, so variable, depending especially on the precipitation regime) the stability reserve is over 2.5. Such a stability reserve can be considered satisfactory, even in the analyzed case, and in accordance with the recommendations of the literature [6, 8, 9]; - in conditions of natural moisture and under the influence of seismic shocks there is a reduction of approx. 44% of the stability reserve, down to a value of 1.409; - in conditions of saturation of the contact area between the strata (situation that can materialize in conditions of moderate precipitation quantitatively and as intensity), the stability reserve of the slope is 1.750; - although these values are supra-unitary, with stability reserves of 40.9% and 75% of the slope, they can be considered as insufficient for this case, close to important objectives and requiring the permanent presence of the staff (people) serving the premises (in this case WWTP Anina). For these situations it is recommended to adopt safety coefficients higher than 2.5; - in conditions of saturation of the contact area between the layers and under the influence of seismic shocks, a reduction of approx. 43% of the stability reserve is observed (compared to the situation with saturated contact area), down to a value of 0.994. This value, being sub-unitary, indicates to us that in such a situation it is very probable that a landslide will take place; - after verifying this result, by using another geotechnical software, a value of the safety coefficient of 0.960 was obtained, ie close (the difference being less than 4%), thus validating the initial result and confirming the high probability of landslide occurrence; - for the last situation analyzed, ie in conditions of saturation of the contact area (occurs in case of heavy rainfall, high intensity) between layers and clays and under the influence of seismic shocks, we also find subunitary value of the safety factor (0.900), indicating again that there is a high probability of sliding. Another important aspect is related to the length on which the slide occurs. Thus in this situation, as we can see from figure 6f, the length on which the sliding surface materializes is approximately ½ of the total length of the potential surface at the contact between the layers. It may seem a more favorable situation, as it would apparently involve moving a smaller volume of material, but this is not the case at all. Thus, due to the radical change of the state of consistency of the clays (the passage, due to the high content of absorbed and adsorbed water, in a plastic state, which allows flowing) the slide will occur at a high speed, therefore the displaced material will travel a much greater distance, immediately endangering the objectives already built. Moreover, the upper part of the clays will move after this first phase because, they, also saturated in turn, would remain practically without support on a slope of about 30°. Therefore, in this situation we would face a complex with 15

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successive transmission or a regressive slide (depending on the moment when the clays at the top of the slope start moving, ie after a time measured in minutes or hours from the production of the initial slide or after seconds or fractions of a second), which would either lead to a further increase in the length of the sliding material or generate additional pushing forces (or a combination of the two effects) with serious consequences for the objectives in the area of influence (the already built buildings of WWTP Anina).

Hypothesis 2 - the sliding surface materializes at the contact between layers I (the intercalation between the layers M1 and M2, the fragmented upper one and the massive lower one) and M1 (Figure 9).

In this case, we must start the investigation from the fact that, as presented in this study, the M1 layer is strongly fragmented, which allows easy penetration of water to the layer I separating it from the lower layer M2, massive (characterized of a water absorption coefficient between 0.3 and 0.7%, according to [1]).

Figure 9. The sliding surface at the contact between layers I and M1

This situation creates favorable conditions for saturation of layer I, and after the maximum water absorption capacity is reached, it will be adsorbed, forming a film (pellicle) of the water between the layer I and the two layers M1 and M2. The appearance of such a water film would lead to a drastic reduction of the resistance characteristics on this contact area (practically the shear strength, expressed by cohesion and the internal friction angle would tend to 0).

Because the software used does not allow us to model the crack system affecting the M1 layer (nor do we have detailed information on this aspect) nor can we estimate a coefficient of structural weakening of the layer in question (determining with satisfactory accuracy requiring complex and long-term geological investigations), in order to present the possibility of a landslide through this area of the slope, the research team analyzed similar situations, encountered in previous studies or presented in the literature.

Therefore, in the case of the formation of a water film at the contact between layer I and M1 (situated above), against the background of the reduction towards 0 of the cohesion and the internal friction angle, there is a high possibility that the latter (layer M1) will enter a sliding motion, either of the entire layer or of large blocks (20 - 40 t), as probably happened in the case of the 2015 landslide.

The speed of movement, the distance at which the movement occurs, the volume of material entrained and implicitly the effects they can produce depend on a number of variables. As found in perhaps the most famous case of such slide (on a film of water formed at the contact between two rock layers), as of the right slope of the accumulation at Vajont (Italy), the speed was about 110 km/h [11], but in the conditions of a slope with much higher inclination and height than in the analyzed case. The high speed with which such landslides occur translates into high energy and implicitly large-scale destructive effects.

The possibility of such a landslide must be considered especially in the event of a seismic shock (caused by natural causes, induced by human activities or a combination of the two), because, as we found in those presented in Hypothesis 1 of production of a landslide, it can reduce the stability reserve, whatever it is, by more than 40%.

4. Conclusions and recommendations Considering those presented in the paper we can draw the following conclusions: 1. There are significant differences in the way in which the rocks that make up the investigated slope were framed. The UP team, through the investigations carried out, came to conclusions, from this point of view, similar to the geotechnical study carried out in October 2015.

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2. Such discrepancies may also lead to erroneous modeling and misinterpretation of the technical condition of the massif (especially in the case of predictive analyzes), which in turn will lead to the design of incorrect technical stabilization solutions, and which will not produce the expected effects (thus endangering built objectives and even people's lives).

3. The stability analyzes performed showed that the slope has a satisfactory stability reserve (over 2.5) only in the most favorable situation analyzed, namely rocks at natural moisture and the absence of external influence factors. However, we point out that such a situation is too unrealistic, and cannot be considered as a benchmark in making a rational decision on the resumption of excavation work on the slope and the construction activities at its base.

4. For the rest of the analyzed situations, the safety coefficient presents either supra-unitary values, but below the value of 2.5 recommended by the specialized literature, or sub-unitary value, indicating an unstable slope.

5. We consider that at present the slope is in a relative state of equilibrium, but any intervention, in the sense of resuming the excavation activities in order to ensure the land area necessary for the construction of enclosures A1, A2, A8 and A11 (according to the construction plan of WWTP Anina [2]) could lead to the reactivation of the 2015 landslide, with its significant extension or to the onset of a new landslide, which materializes on a different slide plan than the original one or which differs by the production mechanism.

6. In these circumstances, the research team decided not to consider any execution of the remaining works related to the completion of the construction of WWTP Anina involving the resumption of excavations on the right side, and, implicitly, not to propose any constructive (technical) solution in this regard.

Recommendations: 1. In view of the results of the stability analyzes obtained for the most unfavorable situations, it is necessary to secure the slope in question immediately, and there is a real possibility of a landslide (or reactivation of the 2015 one) which would endanger objectives already built.

2. Given the short distance between the analyzed slope (relatively stable or unstable under certain conditions), the research team recommends the adoption of a higher safety coefficient than recommended by the literature, in this sense a value of at least 3 is suggested.

3. As such a value is difficult to obtain by simply reshaping the slope, the research team recommends reanalyzing the technical solution (through a specialized consulting company) with retaining wall (in both variants) proposed in the geotechnical study from May 2015. We specify that this technical solution aims only at securing the slope and in no case the resumption of excavations in this area.

Note: When considering the adoption of a technical solution involving the construction of retaining walls, special attention should be given to changing the stress states in the massif (local stresses induced by the foundation and changing the overall stress state of the massif as a whole).

Moreover, the issue of tensions transmitted by the foundation to the massif (whether it is a dug or a drilled foundation) and changes in the global state of tension in the massif is treated on hundreds of pages in the literature [9, 12], and these aspects, taking into account the results regarding the slope stability reserve (especially in unfavorable situations), must be analyzed in detail before a decision is taken to build such structures (retaining walls), so that to involve minimal risks for the executors of the works and for the equipment involved in the process.

Another aspect that must be taken into account, in the case of adopting the solution with retaining walls, is related to the dynamic loads transmitted to the massif (in the form of vibrations) during the excavation/drilling of the foundation.

Dynamic, earthquake-induced loads were taken into account in the stability analyzes. These loads, however, act for short periods of time (maximum of the order of tens of seconds), as opposed to the dynamic loads induced during digging/drilling the foundation.

In the case of dynamic loads induced during the excavation/drilling of the foundation, even if they are lower than the seismic ones (in terms of intensity and acceleration, depending largely on the type of equipment used and the speed of execution of works), they are continuously manifested for much longer periods, and in this case there may be problems caused by the interaction (composition) of the waves transmitted to the slope (especially if digging/drilling is performed in several points simultaneously) and reflected from the slope, in terms of amplitude and frequency.

Therefore, this type of dynamic loads can be seen as possible triggers of a landslide, particularly dangerous, if we consider that it would occur during the execution of works, which involves the presence of people in the area of influence.

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4. Identification and delimitation of another perimeter (with an area of approximately 500 m2) necessary for the construction of premises A1, A2, A8 and A11 (according to the construction plan of WWTP Anina [2]) in a favorable area, which does not involve excavations in the area of the right slopes near WWTP Anina (on Gârliștei valley). In this regard, we recommend initiating a process to remove from the forestry fund an appropriate area of land (north, northeast of the existing buildings) and send this request to Romsilva (and possibly request the involvement of the local and county administration and decision factors in solving the problem).

References [1] P.F.A. Pascalau Gigi, 2015 Geotechnical study for landslide investigation in the area of the Anina wastewater treatment plant, Caraş-Severin county (in Romanian), Contract no. 458/2015, Bucharest [2] ***, 2020 Situation plan, Wastewater Treatment Plant Anina (in Romanian) [3] Corbescu G., 2016 Stabilization of the unstable slope at the Anina wastewater treatment plant (in Romanian), Revista Construcțiilor (Constructions Revue), no. 127, pp. 32-33 [4] S.C. Expert S.R.L. Timișoara, 2015 Geotechnical expertise - Solutions for stabilizing the unstable slopes at the Anina wastewater treatment plant (in Romanian), Contract no. 3531/2015 [5] S.C. Geologic Don S.R.L. Ploiești, 2011 Geotechnical study for the realization of the project "Feasibility study and co-financing application for obtaining cohesion funds for Caraş Severin county for Anina locality" (in Romanian), Contract no. 135/2011 [6] Duncan C.W., Christopher W.M., 2005 Rock Slope Engineering. Civil and mining, 4th edition, Spon Press - Taylor & Francis Group, 431 p., New York [7] Lazăr M., Faur F., 2015 Stability and arrangement of slopes. Examples of calculation (in Romanian), Universitas P.H., 206 p., Petroșani [8] Rotunjanu I., 2005 Stability of natural and artificial slopes (in Romanian), Infomin P.H., 351 p., Deva [9] Stanciu A., Lungu I., 2006 Foundations. Earths physics and mechanics (in Romanian), Vol 1, Technical P.H., 1620 p., Bucharest [10] Technical University of Civil Engineering Bucharest, 2013 Seismic design code P 100-1 (in Romanian), approved by MDRAP [11] Petley D., 2008 The Vaiont (Vajont) landslide of 1963, The Landslide Blog, https://blogs.agu.org/landslideblog/2008/12/11/the-vaiontvajont-landslide-of-1963/ [12] Toderaș M., 2005 Geotechnics and foundations (in Romanian), Universitas P.H., 292 p., Petroșani

This article is an open access article distributed under the Creative Commons BY SA 4.0 license. Authors retain all copyrights and agree to the terms of the above-mentioned CC BY SA 4.0 license.

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IMPROVING THE STABILITY OF THE DIRECTIONAL ROOM G 31-33, HORIZON 210 - EAST, OCNELE MARI-COCENEȘTI SALT MINE,

BY REINFORCEMENT WITH ANCHORS AND SHOTCRETE Dacian-Paul MARIAN1*, Ilie ONICA2 University of Petroșani, Petroșani, Romania, dacianmarian@upet.ro University of Petroșani, Petroșani, Romania, onicai2004@yahoo.com 1

2

DOI: 10.2478/minrv-2021-0031 Keywords: rock salt, rooms and pillars mining, stability, reinforcement, anchors, shotcrete, displacement, numerical model, finite element.

Abstract: The rock salt deposit from Ocnele Mari - Cocenești was mined by the method with rooms and small square pillars, at the levels + 226m and + 210m. Although the saline is not deep, certain instability phenomena (cracks, exfoliations) have occurred in the resistance structures (pillars, ceilings), especially in the G31-33 directional room, horizon 210E. These instability phenomena were also highlighted following the 3D finite element numerical modelling. In order to prevent the degradation of the mining excavations and the resistance structures, the affected surfaces were supported with anchors and reinforced shotcrete. The ceiling of the consolidated section of the G31-33 directional room, horizon 210E is monitored by the systematic measurement, on topographic landmarks mounted on the ceiling, of the vertical and horizontal displacements.

1. Generalities The rock salt deposit from Ocnele Mari is located in the region of the sub-Carpathian hills of Oltenia, and Coceneşti perimeter is located in the eastern part of Ocnele Mari deposit (fig.1).

Figure 1. Geographical location of the deposit of rock salt Ocnele Mari [1]

Corresponding author: Dacian-Paul Marian, Assoc.Prof. PhD. Eng., University of Petroșani, Petroșani, Romania, contact details (University st. no. 20, Petroșani, Romania dacianmarian@upet.ro) *

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From a geomorphological point of view, the relief is hilly to the north, west and east, in the south the region is open to the depression of Rm. Vâlcea - Horezu. The hilly relief has heights between 260 - 500 m, predominating the heights between 350 - 450 m.

Ocnele Mari region, where the deposit is located, belongs to the Getic Depression, which is the outermost unit of the Southern Carpathians.

The rock salt was formed in a halogen basin consisting of a suite of bays and lagoons. The salt deposition took place unevenly inside the basin, depending on the feeding conditions and the morphology of the bottom of the sedimentation basin, the age of the rock salt from Ocnele Mari - Coceneşti being the middle Badenian.

The sedimentary formations of Ocnele Mari region correspond to the Paleogene - Quaternary interval.

The sedimentation process that began in the Paleogene was not continued, with many discontinuities in this process.

From a stratigraphic point of view, the Ocnele Mari region includes Paleogene, Neogene and Quaternary geological formations.

The horizon with rock salt deposits is presented in a lagoon facies, with local distribution, being formed by salt massifs, gypsum and salty marls, in this horizon being included also the rock salt deposit from Ocnele Mari, and the salt massif appears in the axial lifting area from Ocniţa - Ocnele Mari.

The salt deposit from Ocnele Mari has the shape of an elongated lens in the E-W direction, measuring in this sense approx. 7.5 km, and to the N-S, approx. 3.5 km, showing an axial elevation in Ocnita area, with slopes to the N (fig. 2).

Figure 2. Geological cross section through Ocnele Mari rock salt massif [1]

The thickness of the roof deposits varies between 20 m and 50 m in the south and up to 700-800 m in the north, with the sinking of the deposit. The thicknesses of the rock salt deposit are variable, reaching up to laminations in the north and south, the maximum thickness reaching 450 m in the central part of the lens.

The rock salt deposit at Ocnele Mari is flanked on the north and south by two major faults, namely: Stoeneşti fault and Bisericii fault. Inside the rock salt massif, the presence of local micro-tectonic phenomena can be noticed.

From a macroscopic point of view, the rock salt from Coceneşti - Ocnele Mari is presented in the form of alternating strips of white rock salt and dark or blackish gray rock salt, contaminated with films and centimetre fragments of marls or anhydrite nests.

The research drillings and mining workings performed were chemically tested along the entire useful length, and the elements analyzed were: NaCl, CaSO4, CaCl2, MgCl2, Fe2O3 and insoluble substances.

From the point of view of geological research, no distinction was made in the perimeter of Ocnele Mari.

Research - exploration works began in 1952 and intensified between 1988 and 1991.

The rock salt of this deposit has been mined since Roman times, but the systematic exploitation began in the 19th century by bell shape rooms, in the current area of the bathrooms. In 1959, the exploitation of rock salt in the central-western area of the deposit began, through dissolution wells.

The solid way mining of Ocnele Mari - Cocenești rock salt deposit started in 1996, using the mining method with small rooms and square pillars (on a network of 30 x 30 m), in two descending levels, 16 m high, respectively at the levels +226 m and +210 m (mined in the period 2001-2020).

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The dimensions of the rooms were 16 m wide and the pillars 14 x14 m, in the west side and 15 m, with pillars 15x15 m, in the east side. The ceiling between the two horizons is 8m thick. At present it is opening horizon + 190 m, located under a ceiling of 12 m, by report to the horizon + 210 m. This horizon is designed to be exploited with rooms of 15 m, width and pillars of 15x15 m, on both sides of the mining field.

The values of the land surface elevations are between a minimum zmin=301m and a maximum zmax=361 m, which corresponds to a variable depth of position of the floor of the horizon +226 m of H = 75-135 m.

Taking into account the depth and rate of creep stress of the rock salt  , for Ocnele Mari Salt Mine, the constitutive laws of behavior of the rock salt in the underground resistance structures are the following: a) for H  363 m - elastic behavior (stability zone, for   0,36 ); b) for H = 363-555 m– elastic-plastic behavior (relative stability zone, for 0,36    0,55 ); c) for H  555 m - elasto-viscous-plastic behavior (instability zone, for   0,55 ).

In the last 50 years, several determinations of geomechanical parameters have been made for the rock salt from Ocnele Mari, the values of which have been used in the calculations on different analytical and numerical models. Over time, the average values of these parameters, most commonly used in calculations, were as follows: apparent specific weight,  a = 2.15 KN/m3; modulus of elasticity, E=1.5.106 KN/m2; Poisson's ratio,

 = 0.25; compressive strength,  c = 21,700 KN/m2; tensile strength,  t = 1,200 KN/m2; shear strength,  f = 2,300 KN/m2; cohesion, C = 4,000 KN/m2; internal friction angle,  = 30o [2].

In general, following the analytical calculations [3] and numerical analyzes [2], [4] performed, it was concluded that the resistance structures (pillars and floors) from the exploited horizons +226 m and + 210 m are stable, taking into account the relatively shallow depth of the mining excavations, and the phenomena of instability are only local and are determined by the inhomogeneities and natural cracks existing in the rock salt massif.

The numerical model with 3D finite element of Ocnele Mari Salt Mine, calculated in the hypothesis of an elasto-plastic behavior without hardening, highlighted on the horizon +210 m the east side, a single unstable area with plastic behavior (fig. 3), namely the section area G31-33, related to the 210E directional room. This phenomenon of local instability can be explained by the spatial positioning of the underground mining excavations in relation to the configuration of the deposit and the relief of the land surface, which generated a concentration of stress and strain on this area.

The numerical model with 3D finite element is also validated by the instability phenomena observed in the field, which appeared in the rooms, pillars and the ceiling in the area of the directional room 210E, section G31-33 (presented below).

Figure 4 shows the distribution of the maximum (fig. 4.a) and minimum (fig. 4.b) principal stresses at the level + 210E, with the marking of the area affected by instability in the directional room G31-33, horizon.210E.

Figure 3. Horizontal view + 210m - eastern side, with scalar representation of plastic deformation norm (NDP)

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(a)

(b) Figure 4. Horizontal view + 210m - eastern side, with scalar representation of the (a) maximum, in kN /m2 and (b) minimum principal stresses, in kN /m2

2. Reinforcement with anchors and shotcrete of the G31-33 directional room, oriz.210E The directional mining room G, on the east side, horizon + 210 m, is located at an average depth of 110 m, measured from the land surface, of which approx. 40 m is represented by the barren rocks of the roof, formed mainly of marls and clays.

The thickness of the crown pillar is 30 m, and from the crown pillar, at a distance of 16-20 m, is the ceiling of the directional room G, where the equipment of the grinding station is located. The G31, G32 and G33 mining rooms are dug entirely in compact rock salt in the middle of the lens. The structure of the rock salt has an inclined stratification, containing sterile centimetre intercalations, of gray clays. The inclination of clay layers and salt banks is variable, in the range of 20o-40o.

Following the macroscopic analysis of the walls and ceiling of the mining excavations, after 8 years from the completion of the operation of the rooms, areas with different degrees of stability were identified, the working being framed in an area with potential risk of long-term instability, namely: southern wall of room G is more stable and without visible signs of degradation; the northern wall is inhomogeneous, being more pronouncedly affected; the ceiling is stable, but exposed to damage due to the state of stress and strain developed in this area.

The section of the directional room 210E, which showed phenomena of contour instability, is located in the area of the mining rooms G31, G32 and G33, horizon + 210E. This section, where consolidation works have already been carried out, completed in 2020, has a length of: 105 m, in the G directional room; 7.5m, in the transverse rooms G31 and G32; 15m, in the room G33 (fig. 5).

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Figure 5. Situation plan of the area of the directional room G, from horizon. 210E, supported by anchors and shotcrete

In this area of the G31-33 directional room, conditions are created for the exfoliation of rock salt on the free surface of the rooms and the formation of different sized exfoliated rock salt, which can endanger the security of personnel. In order to prevent the degradation of the working, the work (Kovacs, 2012) proposed the full coverage of the surface of underground excavations, the treatment of the negative effect of moisture on clay inclusions and the achievement of an efficient support to ensure the operation of mining working for a projected period of over 40 years.

Due to the inclined stratification and the microtrectonics of the rock salt massif, the bolting system arranged on the ceiling and on the northern wall of the directional room cumulatively shows all three types of effects of the bolting support system, namely: the beam effect (by preventing tangential displacements of the stratification strips); the suspension effect (by catching from the intact massif of the blocks with a tendency to detach, generated by the transversal fissures on the stratification); reinforcement effect (by increasing the resistance of the rock salt massif to a depth of 2.5 m, measured from the surface of the excavations) - Brady & Brown, 2005.

In the project [5], mentioned above, the following underground mining excavations were taken into account in order to be consolidated: a) directional room G: profile of 15x8 m; consolidated length of 105 m (90 m west of the collecting bin and 15 m east of the same bin); ceiling area of 1,575 m2; the surface of the northern wall of 480 m2 and the southern wall of 840 m2; b) transverse rooms G31 and G32: profile 15x8 m; length of 7.5 m; ceiling area of 225 m2; wall area 240 m2; c) the transverse room G33, with a length of 15 m and the other geometric parameters identical to those of the other two transverse rooms, added together.

From the sum of the above areas, resulted a total area, necessary to be consolidated/reinforced, at the level of the ceiling of 2,025 m2 and at the level of the walls of 1,800 m2.

Following the monitoring of the ceiling of the consolidated section of the 210E directional room, it was proved that the implementation of this project, in 2020, is a successful experiment (as well as the one performed at Ocna Dej Salt Mine, in the transversal gallery 310 m, related to the rooms of the pre-crushing plant), therefore this project can be a model that can be used in similar conditions at Ocnele Mari Salt Mine or other salt mines in Romania.

The anchor and shotcrete support method [6], applied under the conditions of the G31-33 directional room, horizon + 210E has the following main technical characteristics: 1) The ceiling, in the area where the equipments is located, was supported by anchors (PC52-  24 , 2.5 m long, 1 m spaced) with a density of 1 anchor/m2, fixed with LOKSET polyester resins, wire mesh welded (Buzau type) mm, with meshes of 100/100 mm and mechanical shotcrete, with a thickness of 0.1 m;

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2) The north wall and the walls of rooms G31, G32 and G33 were supported with anchors, welded wire mesh and mechanical shotcrete, with a thickness of 0.1 m (with the parameters 3) The southern wall was supported by a mechanical shotcrete with a thickness of 0.05 m.

The materials used to apply the anchoring/bolting technology are: PC-52 anchors; metal plates; Buzau type metal mesh; corrosion protection materials; LOKSET fixing cartridges with synthetic (chemical) resins.

The PC-52 anchor has a diameter of 24 mm. The front end of the anchor is cut diagonally at an angle of o 45 , and the other end is threaded with M20, 150 mm long. The threaded portion of the anchors was protected against corrosion with an ICOSIT POXICOLOR epoxy resin. The plate is made of OL 35 steel sheet, square in shape, with a side of 150 mm, provided in the center with a hole of  22 mm. Buzău type  8 mm welded wire mesh, with 100x100 mm mesh, is made of 2x4m panels.

The technology of mounting the support with anchors and shotcrete (fig.6) consists of the following successive operations: a) scaling the exfoliated surface, b) drilling holes for anchors, with a length of 2.5 m and a diameter of 28 mm, according to the support monograph; c) preparation of the package with LOKSET chemical fixing cartridges; d) preparation of the metal anchor and the P90 perforator, with the telescopic column; e) inserting into the hole of 1.5 pieces LOKSET HS Slow ampoules, 500 mm long and 24 mm in diameter; f) inserting the anchor to the bottom of the hole, so that the 5-10 cm threaded portion remains outside the hole, followed by fixing it in the hole with 2 wedges and leaving an interval of 24 hours to strengthen the synthetic resin; g) mounting the plastic plate, the metal mesh (without touching the rock salt massif) and the metal plate which, then, will be tightened with the M20 nut, at a moment of 20 kgf .m, using a torque wrench; h) anti-corrosion protection of the anchor thread with Mapeter resin; i) application of shotcrete with a thickness of 0.1 m, after an interval of 48 hours.

Shotcreting was done in successive layers 2-3 cm thick, with the help of an ALIVA 240.5 shotcreting machine.

The formula for shotcrete mortar is as follows: Portland I cement 42.5 - 600 kg/m3; sand sort 0-3mm - 0.4 m3; sand sort 3-7 mm - 0.4 m3; gravel 7-15 mm - 0.3 m3; grip accelerator (Sigunit or Bara Gunit) -33 kg; water - 200-250 l.

Prior to the formation of the final layer of shotcrete, a layer of blocking shotcrete was applied directly to the surface of the rock salt massif, with the following formula: Portland I cement 42.5 - 600 kg/m3; sand sort 0-3mm - 1.1 m3; socket accelerator -33 kg; salt water 0.15-0.25 kg salt/l.

Figure 6. Cross section through directional room + 210E, with layout of anchors / bolts on the contour of the mining workings [5] 1-bearing anchor; 2-mesh tension anchors: 3-wire mesh; 4-reinforced shotcrete; 5-single shotcrete; 6- plastic plate; 7-anchor plate; 8-nut M20; 9-ampoule of polyester resins

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3. Topographic monitoring of the displacements of the ceiling of the directional room G31-33, horizon 210E In December, 2020, 24 topographic landmarks were placed on the ceiling of the G31-33 directional room, horizon 210E, in the area of the underground grinding plant of Ocnele Mari Salt Mine, an area supported by anchors and shotcrete. The objective of the topographic landmarks was to monitor the movements of the salt block that tends to detach from the ceiling of the room, and the first measurement was performed on 15.12.2020.

To perform the measurements, a ”measuring base” consisting of points 210E and terminal B1, located on the floor of the directional room 210E, was established. For these two points, topographic measurements were performed in the particular reference system of the mine, determining the coordinates Y (after the direction W-E), X (N-S) and Z (after the vertical). Starting with the points of the measurement base, measurements were performed on the 24 landmarks, with the help of the total station Leica -TS 06, using its measurement function without prism, determining the X, Y and Z coordinates of each landmark. In June 2021, the second measurement was performed. The time interval between the first and second measurements was 6 months.

Following the measurements, the horizontal displacements ΔX and ΔY and the level differences ΔZ were calculated, so that the vertical displacements and the rate of displacements of the ceiling surface of the underground excavation were obtained.

Given the very short interval (only 6 months) between the two measurements and the relative accuracy of the measurements, we consider that at this stage the results are not relevant. As the time interval between the first and subsequent measurements increases, significant conclusions can be drawn about the evolution of the monitored mining deformation phenomenon over time and a number of forecasting functions can be developed.

However, a concentration of vertical displacements towards the 31G pillar area of max. 10-15 mm (fig. 7.a), of the horizontal displacements along the X axis, in the area of the 31G and 32G pillars, of max. 3-5 mm and less towards the 33G pillar (fig.7.b) and of the horizontal displacements along the Y axis, of max. 8-10 mm, at the limit with the 31G pillar and with the room between this pillar and 32G (fig.7.c).

Even if the monitoring period is irrelevant, a concentration of the deformations of the ceiling of the directional room 210E can be found in the area of the pillars and towards the corner between the pillars and the ceiling of the mining working. These observations are in full agreement with the concentration of stresses on the row of pillars located in the immediate vicinity of the monitored working.

a)

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b)

c) Figure 7. (a) Vertical along the Z axis, (b) horizontal along the X axis and (c) horizontal, along the Y-axis displacements of the ceiling of the directional room 210E, June, 2021 - scalar representation

4. Conclusions Following the calculations performed by analytical methods and the analyzes by numerical methods, it was proved that the underground mining excavations and the resistance structures from Ocnele Mari-Cocenești Salt Mine are stable.

There are phenomena of local instability generated by inhomogeneity and natural fissures in the rock salt massif or due to the local concentration of stress and strain, due to the relative spatial position of the mining excavations from the two exploited horizons, + 226m and + 210m, in relation with the configuration of the deposit and the relief of the land surface.

An area affected by instability is the G31-33 directional room, horizon + 210E, where a series of cracks and exfoliations were found on the contour of the excavations. This area was also highlighted in numerical 3D models, by the presence of the phenomenon of rock salt plasticization and by the concentration of stresses in this area.

The area of the G31-33 directional room, horizon 210E, was reinforced by support with 2.5m long cemented anchors and reinforced shotcrete.

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Following the monitoring of the displacements of the ceiling of the consolidated directional room, an obvious stabilization of it was found and a distribution of the maximum vertical and horizontal displacements in the areas of the stress concentrators in the vicinity of the pillars.

References [1] Marica D., 2011 Study of the stability of mining excavations at the Ocnele Mari salt mine in order to increase the degree of work safety, PhD thesis, University of Petroșani.

[2] Onica, I., Cozma, E., Marica, D.P., 2011 Stability Analysis of the Rock Salt Rooms and Pillars of the Ocnele Mari Saline with the Aid of the 2D Finite Element Modelling, Annals of the University of Petroşani, Mining Engineering, Vol.12 (XXXIX), pag.7-17.

[3] Hirian, C., Georgescu, M., 2012 Stability of old salines in Romania - condition of their use for various fields, Universitas Publishing House, 2nd Edition, 2012.

[4] Onica, I., Marian, D.P., 2016 Applications of the finite element method in the analysis of stability of grounds and underground structures, Ed. Universitas, Petroşani.

[5] Kovacs, F., 2012 Minimal flow of grinding rock salt in the underground of the Ocnele Mari Salt Mine, Râmnicu Vâlcea Mining Branch.

Volume II - Consolidation of the area of the grinding flow. Technical project phase and specifications, Symbol 3/4/2012, S.C. DACITROM SRL Cluj-Napoca.

[6] Brady, B.G.H., Brown, E.T., 2005 Rock Mechanics for underground mining, Third edition, Kluwer Academic Publishers, New York, Springer Science + Business Media, Inc.

This article is an open access article distributed under the Creative Commons BY SA 4.0 license. Authors retain all copyrights and agree to the terms of the above-mentioned CC BY SA 4.0 license.

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ANALYSIS OF A REPLACEABLE CUTTING TOOTH OF BUCKET CHAIN EXCAVATOR Zoltán VIRÁG1*, Sándor SZIRBIK2 1

University of Miskolc, Institute of Mining and Geotechnical Engineering, Miskolc, Hungary, gtbvir@uni-miskolc.hu 2 University of Miskolc, Institute of Applied Mechanics, Miskolc, Hungary, sandor.szirbik@uni-miskolc.hu

DOI: 10.2478/minrv-2021-0032 Keywords: bucket chain excavator, cutting teeth, detachable joint, cutting load, FEA Abstract: This paper briefly outlines the design of replaceable cutting teeth of bucket chain excavator, which are attached to a holder with a detachable joint. The description of the rock cutting process is very complex, so the investigation of the effect of lateral forces is complicated through cutting tests. We use accordingly numerical analysis to examine some segments of the cutting process. Our main objective is to present the finite element analysis of cutting teeth in which the linear increase of the lateral force is taken into consideration.

The finite element analysis is a powerful technique, which is enabled to compute the stress and displacement distribution in cutting teeth. The simulation results have shown that the maximum stresses decrease if the lateral force increases. The geometry of the optimized cutting teeth will be safe under the given loading conditions.

1. Introduction Bucket wheel and bucket chain excavators are used in open pit coal mining are subjected to excessive loads during cutting because of the interaction between the working face and the excavation components. High loads and unexpected shocks produce numerous damages to the excavator components leading to increased energy consumption and lower production rate. Radu et al. [1] performed a study of the forces acting on the shaft of the bucket wheel was conducted to reduce the mentioned issues and improve the quality of the excavation process.

An important and complex issue in mining is also rock cutting mechanization. The high cutting tooth wear and the high specific power demand are the long-standing problems of mining techniques. The new cutting tooth was designed to eliminate problems. Rock cutting tests were carried out, where winning experiments on the large sample from the mine were made using chisels modelling the in-plant winning chisels (cutting teeth), with cutting parameters close to reality [2].

To determine the geometric configuration of the cutting teeth and the cutting edges the knowledge of the mining technology is inevitable. The measurement data of cutting is collected and registered by a computer aided measurement system. On rock samples, we recorded 165 measurement cycles. In each measurement cycle, the following data and cutting characteristics were recorded: cutting direction, form, depth, average chip area, average cutting force FV, average pressing force FR and average lateral force FO. As a result of the measurements, a new cutting geometry was developed [2]. The experiments prove that it should pay attention to the wears and the geometry of cutting teeth because of the increasing of the cutting, pressing and lateral force. Considering the laboratory cutting test results the FEA was created for further investigations for replaceable cutting teeth of bucket chain excavators. The results lead to determine the most critical point of the cutting tool, which help us to select the proper high strength steel that tolerates the extreme loads.

*

Corresponding author: Zoltán Virág, Assoc. Prof., University of Miskolc, Miskolc, Hungary, (H-3515 MiskolcEgyetemváros, gtbvir@uni-miskolc.hu) 28

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2. Model geometry and loading To investigate the distribution of the main stresses in the cutting tooth, we set up a finite element model.

Consider the solid model shown in Figure 1, consisting of a holder, apart from the cutting edge and an optimized cutting tooth. The cutting tooth is jointed into the holder as a removable piece. The tooth holder is a steel rectangular structural tube and of course, it is possible the remaining parts of the structure are made of different grades of steel.

Fig. 1. Assembly of solid models (3 parts) 1 - cutting tooth, 2 - cutting edge, 3 – holder

The geometrical model of the tooth is illustrated in Figure 2. The material is assumed to be isotropic elastic: the material properties are Young’s modulus of E = 2.1×105 MPa and Poisson’s ratio of ν = 0.3. The finite element method, which is a very popular numerical technique, is used to numerically solve differential equations arising in engineering problems. The main concept of the technique is that the geometry of structure subdivides into non-overlapping small parts, so-called finite elements, which are implemented by the construction of a mesh. The conventional element types possess simple shaped geometry with well-defined stress displacement relationships. Thus, the sufficiently refined meshes need to ensure that the results from simulations are adequate. Accordingly, the cutting tooth is meshed into finite elements, which are 10-node tetrahedral elements.

Fig. 2. FE model of cutting tooth

The aim of previous work [3] is to simulate the cutting load from real cutting conditions on the surface, which is painted with red colour in Figure 3. The resultant force from the pressure on the surface consists of three components: cutting force FV, lateral force FO and a pressing force FR.

Fig.3. Cutting, lateral and pressing force 29

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The force components were determined by means of laboratory cutting experiments [2]. We assume that now the values of the resultant of cutting and lateral forces are 100 kN, and the pressing force is always 100 kN. To investigate the rock cutting action for cutting forces in different directions, various direction angles are defined. The direction angle α, which is measured in degrees positive clockwise between the direction of cutting force and the y-axis of the global coordinate system, specifies the magnitudes of lateral and cutting forces. Thus FR = F = 100 kN (1) FV = F cos α (2) FO = F sin α (3) are imposed on the appropriate surface as specified loads.

Because of the detachable contact joint, we should describe five contact pairs between the appropriate surfaces of the tooth and holder in the finite element analysis. The contact pair consists of the two contact surfaces. One of them in the pair is selected to be the contactor surface on the tooth and the other contact surface to be the target surface on the holder. For simplicity, the contact surfaces of the holder are regarded as stationary, rigid surfaces. It follows that these surfaces are used in our model to simplify the contact searching instead of modelling the holder as a solid structure. We assume that the coefficient of friction is equal to zero between the contact surfaces. Under these conditions, we should solve this contact problem by using the finite element method. Further details of contact problems are presented in [4], [5].

3. Analysis results To preserve the integrity of the teeth, the maximum stresses should be kept under the proportional limit of the material. The finite element analysis helps accordingly to qualify the strength of the new cutting tooth.

As appeared from the numerical simulation the maximum effective stress is about 900 MPa and it occurs in front of the tooth (see Figure 4a-d). However, the stresses decrease quickly below 60 MPa in the remaining part and so in the shank of the tooth.

(a)

(b)

(c) (d) Fig. 4. Effective stress (von Mises) in the tooth: (a) α = 0˚; (b) α = 10˚; (c) α = 20˚; (d) α = 30˚

Figure 5a-d shows the magnitude of displacement, colour-coded at each point in the structure, to visualize the calculated deformation. The maximum displacement occurs also in front of the tooth, where the loading condition is imposed. The maximum value of deformation is 0.532 mm (see Figure 5d). In the remaining part, displacements decrease also quickly.

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(a)

(b)

(c) (d) Fig. 5. Magnitude of displacement in the tooth: (a) α = 0˚; (b) α = 10˚; (c) α = 20˚; (d) α = 30˚

The corresponding results after changing direction angle are tabulated in Table 1, which contains the maximum effective stress σmax and the maximum displacement umax. As mentioned previously, angle α is measured in degrees, and according to Table 1, four different values are employed, namely 0, 10, 20 and 30.

Table 1. Maximum values of numerical results

α

σmax [MPa]

umax [mm]

0˚ 10˚ 20˚ 30˚

933.3 884.9 850.3 829.3

0.426 0.389 0.422 0.532

The simulation results show differences in the values of displacements. However, the stresses decrease if the angle increases. We remark that these results show good analogy with those obtained in the previous study [3], where the whole structure is modelled as a solid structure. Finally, the theoretical optimized cutting tooth for the bucket chain excavator is realized.

4. Conclusions It is established that the development of cutting teeth improves by using finite element analysis that is applicable to compare easily different types of teeth. It leads to an assessment of the effect of the main parameters on the behavior of the geometric configuration of the cutting teeth. Consequently, the results of finite element analysis show that the head of the cutting tooth is the most critical point and so we can draw that high strength steel will be adequate because of the extreme loads. The FEA results can be useful in practice.

Therefore, it is important to know that the cutting teeth are properly designed, made from proper materials, and constructed considering loading during their lifespan.

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References [1] Radu, S. M., Popescu, F. D., Andras, A., Kertesz, I., Tomus O. B. 2018 Simulation and modelling of the forces acting on the rotor shaft of BWEs, in order to improve the quality of the cutting process, Annals of the University of Petrosani, Mechanical Engineering 20 [2] Ladanyi, G., Sumegi, I., Virag, Z. 2007 Laboratory rock cutting tests on rock samples from Visonta South Mine, Annals of the University of Petroşani, Mechanical Engineering, 9, pp. 209-218.

[3] Ladanyi, G., Virag, Z. 2016 Examining the bucket wheel excavator’s bucket after renewal, Annals of the University of Petrosani: Mechanical Engineering 18, pp. 93-98.

[4] Bathe, K. J. 1996 Finite Element Procedures, Prentice-Hall, Inc., New Jersey.

[5] Wriggers, P. 2006 Computational Contact Mechanics, Spinger-Verlag Berlin Heidelberg.

This article is an open access article distributed under the Creative Commons BY SA 4.0 license. Authors retain all copyrights and agree to the terms of the above-mentioned CC BY SA 4.0 license.

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SIMULATION OF THE VIBRATIONS PRODUCED TO THE HUMAN BODY DURING OPERATION OF THE BUCKET WHEEL EXCAVATORS. A CASE STUDY OF ERc 1400-30/7 TYPE EXCAVATOR Ildiko BRÎNAȘ1* 1

University of Petroșani, Petroșani, Romania, kerteszildiko@ymail.com

DOI: 10.2478/minrv-2021-0033 Keywords: bucket wheel excavator (BWE), dynamic time response, global damping, sensor, excavator operator.

Abstract: The paper deals with the analysis of the dynamic response over time of the excavator boom during operation. For a start, we determined the variation in time of the forces acting on the rotor shaft, due to the excavation. These forces have high values and a slow variation over time, which depends on the rotation speed of the bucket wheel and the number of buckets installed on it. A virtual model of the BWE boom was proposed, for which the dynamic response in time due to the excavation forces was determined, for a point in the main cabin of the BWE. A virtual sensor has been attached to this point corresponding to seat of the operator. The simulation of the dynamic response over time was performed taking into account a global damping of 2% of the critical damping. The simulation was performed both for the excavation of a homogeneous material and for the case of a shock (a sudden appearance of an inclusion of hard material during the cutting of the homogeneous material).

1. Introduction The bucket wheel excavator (BWE) is part of the technological system used in open-pit lignite exploitation, used at the beginning of the technological process, where it excavates large quantities of material.

The BWE model ERc 1400-30/7 is the most widespread in the mines situated in the Oltenia Basin, and it is used to perform all simulations within the paper (Figure 1).

Figure 1. ERc 1400-30/7 model bucket wheel excavator

Corresponding author: Ildiko Brînaș, lect. Ph.D. eng., University of Petrosani, Petrosani, Romania, (University of Petrosani, 20 University Street, kerteszildiko@ymail.com) *

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The operating tool is the bucket wheel. It performs a rotation in vertical plane and a horizontal slewing as well as a vertical rising-lowering together with the boom [1], [2].

The present paper proposes a new approach to the analysis of the response in time to the loads generated during the excavation process, based on a virtual model of the excavator boom. An analysis of the vibrations at the boom of a BWE was performed in [3] by measuring the accelerations resulting from the sequence: starting the bucket wheel followed by starting the conveyor belt and subsequently stopping both subassemblies.

The measurement of vibrations and modal frequencies was performed in [4] following the generation of a mechanical impulse obtained by shooting the cables used to suspend a weight to the bucket wheel in two scenarios, with the bucket wheel suspended and touching the coal-face.

The boom of the ERc 1400-30/7 excavator is a spatial structure (Figure 2) subjected to loads, and it can be divided into 3 sections: 1. A joint section between the boom and the BWE structure, which allows for both vertical and horizontal plane movements; 2. The middle section on which the conveyor belt is mounted for the discharge of the excavated material; and 3. The bucket wheel support section on which the drive mechanisms, as well as the boom hoist cable attachment device, are mounted [5].

Figure 2. Sections of the BWE boom

During the excavation process, the energy consumption at the bucket wheel level has two major components [5]: the energy needed for cutting the material from the face and the energy needed for lifting the loose material that results from excavation. Between these, the energy necessary for cutting the material is predominant, between 60 to 90% of the energy necessary for operating the bucket wheel.

2. Simulation and modeling of the resultant force acting on the bucket wheel during excavation In order to determine the resultant force acting on the bucket wheel shaft, SOLIDWORKS was used to build a model of the ERc 1400-30/7 bucket wheel in its updated version [6], equipped with nine cutting– loading buckets and nine cutting buckets. Figure 3 also shows the forces acting on each bucket during excavation: The resultant cutting forces, the forces corresponding to the weight of the lifted material and the inertia forces caused by unloading the buckets. The cutting forces are tangential to the circle described by the cutting edges. The forces corresponding to the weight of the material are parallel and with the same directional as gravitational acceleration [6].

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Figure 3. The bucket wheel model and forces acting on the buckets

Figure 4 shows the variation diagram of the force corresponding to the weight of the material, for one cutting-loading bucket. The first part of the chart (ascending line) corresponds to loading of the cut material, the horizontal part corresponds to the lifting of the loaded bucket up to the discharge level, and the descending part corresponds to the discharge of material on the conveyor.

Figure 4. Diagram of the forces corresponding to the weight of the material over time

Figure 5 presents the variation diagram of the cutting forces. These act both on the cutter–loader and the cutter type buckets.

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Figure 5. The diagram of the cutting forces acting on both the cutter–loader and cutter buckets.

The time of the simulation corresponds to two complete rotations of the bucket wheel. The offset time between two successive curves seen in figures 4 and 5 is depending on the rotation speed of the bucket wheel.

For this BWE model the nominal speed is 4.33 rpm which is equivalent to a discharge rate of 39 buckets/min.

The excavation time is influenced by the maximum excavation height, which is H=7.5 m in this case.

After running the simulation in SOLIDWORKS Motion Analysis, the variation of the resultant force at the bucket wheel shaft is determined for homogenous material excavation, as shown in figure 6. Based on the plot it can be seen the values of this force are between 77kN and 102kN, with an average value of 89.5kN.

Figure 6. The variation of the resultant force at the bucket wheel shaft during homogenous material excavation

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The appearance of an inclusion of hard material during the excavation of homogeneous material is a probable event that causes vibrations with higher amplitudes, causing an increase in the cutting forces exerted on the buckets.

In order to simulate the phenomenon, we considered this hard formation appears during the first rotation at the 4th bucket, with a diagram of the cutting force as shown in figure 7.

Figure 7. The diagram of the cutting forces acting on buckets in the case of a hard inclusion of material

The simulation was run similarly in SOLIDWORKS Motion Analysis for this scenario, and the variation of the resultant force at the bucket wheel shaft is determined as shown in figure 8.

Figure 8. The variation of the resultant force at the bucket wheel shaft in the case of a hard material inclusion 37

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3. Modeling of the ERc 1400-30/7 BWE boom Based on the manufacturer specifications for this type of BWE, SOLIDWORKS software was used to develop a model of its boom. This will be used to analyze the time response to the loads generated by the excavation process [2].

3.1. Modeling of the bucket wheel A simplified model of the bucket wheel was developed at real scale, with its dimensions as noted in figure 9. In order to have the same static load acting on the boom as in the case of the real part, the material on the model was defined to have a δ=373 kg/m3 density. The placement of the bucket wheel model is shown in figure 10, where the coordinate system (X, Y and Z directions) that will be referred to during the research is also highlighted.

Figure 9. The bucket wheel model and its dimensions

Figure 10. Placement of the bucket wheel model on the boom

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3.2. Modeling of the drive chain of the bucket wheel The elements that make up the kinematic chain of the excavator bucket wheel drive system are simulated using a uniformly distributed mass as shown in Figure 11.

Figure 11. Modeling of the drive chain of the bucket wheel

3.3. Modeling of the conveyor belt inside the boom The conveyor belt mounted inside the structure of the excavator boom was modeled by a remote type mass whose value according to the documentation is 25,000 kg (Figure 12).

Figure 12. Modeling of the conveyor belt

3.4. Modeling of the boom hoisting cables The 10 cables used to raise and support the boom of type WS40-6 x36 galvanized steel zinc alloy are modeled by two springs (Figure 13) subjected to elongation, which have the constant of elasticity equal to 35,000,000 N / m for one cable.

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Figure 13. Modeling of the boom hoisting cables

The main static loads to which the BWE boom is subjected and the elements that generate these loads are shown in Table 1, and also the SOLIDWORKS® Simulation type of load used is also specified. Both the conveyor belt mounted on the rotor arm and its kinematic drive chain are vibration generators. In the adopted model we considered only the static effect of their presence, thus being able to highlight the dynamic response of the boom structure under the action of excavation forces.

Table 1. Static loads acting on the BWE boom

No

External load

Unit

Value

Solidworks type of load

1 2 3 4

Conveyor belt inside the boom Drive chain of the bucket wheel Bucket wheel model Boom hoisting cables

Kg Kg Kg N/m

25.000 29.500 39.600 2x35.000.000

Remote Loads/Mass Distributed Mass Part Spring

3.5. Modeling the operator cabin and its supporting structure The real operator cabin, its placement on the boom and the support structure are shown in Figure 14 a and b. This was modeled in SOLIDWORKS® using the structure developed shown in figure 15.

a

b Figure 14. The main BWE operator cabin

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Figure 15. The model of the BWE operator cabin

All the components developed in the previous paragraphs are assembled to obtain the complete model of the BWE boom as seen in figure 16.

Figure 16. Complete model of the BWE boom assembly

3.6. Objectives of the simulation of the excavator boom The simulation of the excavation process and the analysis of its effects on the excavator boom was performed using SOLIDWORKS® Simulation application. Figure 17 shows the nodal network of the boom structure of beams. Also in this figure, the position of a virtual sensor that is placed on the floor of cabin the main operator cabin is highlighted. This sensor will be used to record the response of the structure during the dynamic analysis.

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Figure 17. The nodal network of boom structure and the virtual sensor placement

4. Dynamic analysis of the time response of the ERc 1400-30/7 excavator boom model 4.1. Theoretical aspects of the time response analysis The dynamic time response analysis implies that the load applied to the structure is an explicit function of time, mass, and damping properties with the characteristic equation expressed as [7, 8]:

 M  d  C  d   K  d  F (t )

(1)

where [M] is the mass matrix; [C] is the damping matrix; [K] is the elasticity matrix; F(t) is the vector of nodal loads, expressed as a function of time; and d is the unknown vector of nodal displacements.

The results of the dynamic time response analysis for both permanent and transient regime, were obtained by interrogating the virtual sensor previously presented. Graphs of the variation of accelerations and deformations due to the excavation force for the X, Y and Z directions were drawn. The force that will produce the vibration in the boom structure is variable over time, being generated by the whole excavation process (cutting, lifting and unloading the material). Figure 18 shows how the resultant excavation force is applied to the bucket wheel shaft.

Figure 18. The excavation force applied to the bucket wheel shaft 42

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The properties of the dynamic time response analysis of the BWE boom structure are presented in figure 19, where the number of modal frequencies taken into consideration, the type of solving algorithm, the time range and its increment step were defined [9].

Figure 19. Defining the properties of the dynamic time response analysis

Figure 20 shows the finite element meshing process for the structure of the BWE boom. It can be seen that it has an inhomogeneous structure, depending on the type of the components forming the boom (Solid or Beam).

Figure 20. Meshing of the BWE structure into finite elements

4.2. Dynamic time response analysis during permanent regime We presented in figures 21, 22 and 23 the graphs of the accelerations resulted on the X, Y and Z directions, resulted from the dynamic time response analysis of the forces during permanent excavation regime.

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Figure 21. Acceleration on direction X during permanent regime

Figure 22. Acceleration on direction Y during permanent regime

Figure 23. Acceleration on direction Z during permanent regime 44

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Figures 24, 25 and 26 present the graphs of the oscillation amplitude of the boom on X, Y and Z directions during permanent excavation regime.

Figure 24. Oscillation amplitude on direction X during permanent regime

Figure 25. Oscillation amplitude on direction Y during permanent regime

Figure 26. Oscillation amplitude on direction Z during permanent regime

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4.3. Dynamic time response analysis during a shock The dynamic time response analysis was performed in case of a shock, when the buckets hit a hard material inclusion during excavation. Figures 27, 28 and 29 show the graphs of the accelerations on direction X, Y and Z in this case.

Figure 27. Acceleration on direction X in case of a shock

Figure 28. Acceleration on direction Y in case of a shock

Figure 29. Acceleration on direction Z in case of a shock 46

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Figures 30, 31 and 32 present the graphs of the oscillation amplitude of the boom on X, Y and Z directions in the case of a shock due to hard material inclusions during excavation.

Figure 30. Oscillation amplitude on direction X in case of a shock

Figure 31. Oscillation amplitude on direction Y in case of a shock

Figure 32. Oscillation amplitude on direction Z in case of a shock

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5. Conclusions A virtual model of boom of the ERc 1400-30/7 BWE was created in order to perform the time response analysis under the action of the excavation forces. The mathematical model of the resultant excavation forces was defined as the main source of vibration of the boom and the static loads acting on the boom were also determined.

In both scenarios considered, first the excavation of homogenous material and second a shock produced by the sudden appearance of hard material formations, the dynamic time response analysis performed for a global damping of 2% of the critical damping, is characterized by: - Transient period caused by the beginning of the excavation process; - Transient period caused by the sudden appearance of harder formations of material; - Permanent regimes corresponding to the excavation of homogeneous material.

Analyzing the acceleration variation graphs it can be concluded that: - The accelerations are variable in time having an oscillating character; - The highest values of acceleration are obtained for the X and Y directions; - The acceleration variation graphs for all directions are symmetrical about the time axis.

From the point of view of the deformations in dynamic regime, the following conclusions result: - The deformations are variable in time and have an oscillating character; - The largest deformations are obtained for the Z direction.

In general practice, expressing the vibrations in the form of deformations is suitable for low frequencies, while expressing of vibrations in the form of accelerations is suitable for high frequencies. The BWE boom model adopted in this paper, allows a good approximation of both approaches, deformations or accelerations, and can be quickly adapted for other types of BWE. The results obtained from the simulation are comparable with the measurements performed in-situ for this type of excavator [10]. The concordance between the simulation results on the virtual model and the acceleration measurements performed, validates the adopted model.

Both the in-situ measurement results and the simulation results, show that the vibrations generated by the excavation process do not cause accelerations in the main operator cabin that exceed the vibration levels regulated by law, regarding the vibration exposure transmitted to the body of the BWE operator: - 1.15 m/s2 (8 hrs / day) - the limit value of daily professional exposure; - 0.5 m/s2 (8 hrs / day) - value of the daily exposure from which the action is triggered [11].

However, an important future direction of research, which will be disseminated in a future research paper, is to find vibration damping solutions applicable to the BWE operator cabin. These would cause a smoothing of the oscillation variation curves, especially those that take place in the dominant (vertical) direction, thus leading to increased comfort.

Acknowledgements This paper represents the stage one results within the Research Project financed by the University of Petroşani: Modeling and simulation of industrial equipment components using CAD/CAM/CAE technologies, acronym MSCEIT (Modelarea şi simularea componentelor echipamentelor industriale utilizând tehnologii CAD/CAM/CAE, acronimul MSCEIT).

References [1] Nan M.S., 2007 Rotary excavator process excavation parameters (in Romanian), Universitas Publishing, Petroşani [2] ROMINEX S.A. Timişoara, 2007 Coupe wheel excavator ERc 1400-30/7 modernized. Operating instructions. Maintenance and reparations (in Romanian).

ROMINEX S.A., Timişoara [3] Jiang Y.Z., Liu C.J., Li X.J., He K.F., Xiao D.M., 2018 Low-Frequency Vibration Testing of Huge Bucket Wheel Excavator Based on Step-Decay Signals, Hindawi Shock Vib., DOI: https://doi.org/10.1155/2018/6182156

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[4] Gottvald J., 2010 The calculation and measurement of the natural frequencies of the bucket wheel excavator 1320/4x30, Transport, DOI: https://doi.org/10.3846/transport.2010.33 [5] Popescu F.D., Radu S.M., Kotwica K., Andras A., Kertesz (Brînas) I., 2019 Simulation of the Time Response of the ERc 1400-30/7 Bucket Wheel Excavator’s Boom during the Excavation Process, Sustainability, https://doi.org/10.3390/su11164357 [6] Brînaș I., Andraș A., Radu S.M., Popescu F.D., Andraș I., Marc B.I., Cioclu A.R., 2021 Determination of the Bucket Wheel Drive Power by Computer Modeling Based on Specific Energy Consumption and Cutting Geometry, Energies, https://doi.org/10.3390/en14133892 [7] Kurowski P.M., 2015 Engineering Analysis with SOLIDWORKS® Simulation 2015, SDC Publications: Mission, KS, USA [8] Kurowski P.M., 2016 Vibration Analysis with SOLIDWORKS® Simulation 2016, SDC Publications: Mission, KS, USA [9] Akin J.Ed., 2009 Finite Element Analysis Concepts via SolidWorks, World Scientific, 2009 [10] Lazăr M, Rîşteiu M., Andras I., Predoiu I. 2018 In situ measurements regarding the BWE boom using accelerometers and strain gauges at BWEs operating in CEO open pits. Gór. Odkryw 2018, LVIX, 86–93 [11] Platon S.N., Badea D., Antonov A., Ciocîrlea V., 2013 Work security and safety guide on mechanical vibrations (in Romanian), INCDPM, Bucureşti, 2013

This article is an open access article distributed under the Creative Commons BY SA 4.0 license. Authors retain all copyrights and agree to the terms of the above-mentioned CC BY SA 4.0 license.

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ROMANIAN CARBONATE ROCKS CUTTABILITY ASSESSMENT USING LINEAR CUTTING TESTER Andrei ANDRAȘ1*, Florin Dumitru POPESCU2 1

University of Petroșani, Petroșani, Romania, andrei.andras@gmail.com 2 University of Petroșani, Petroșani, Romania, fpopescu@gmail.com

DOI: 10.2478/minrv-2021-0034 Keywords: microwave, excavation, carbonate rocks, point attack picks, mechanical properties, linear cutting test Abstract: The paper presents the state-of-the-art on the microwave assisted mechanical rock cutting by presenting actual findings and tendencies in the field in international literature, and the activities performed during the intermediate stage and the results obtained by the team from the University of Petroșani as partner within the ERAMIN-ERANET-MIWACUT research project.

1. Introduction In general, mechanical excavation, hard rock cutting and drilling and blasting are the most common methods / technologies when it comes to rock mass extraction. Mechanical cutting or excavation is more advantageous as compared to the classic drilling and blasting for a number of reasons: continuous exploitation versus cyclic one, less effect on the surrounding rock mass, better safety and less environmental impact.

However, the technical limitation of the mechanical machines in certain geotechnical conditions is the biggest disadvantage. With the scope of overcoming these limitation, as well as production increase, excavation tools wear reduction or replacement of the drill and blast method, there are numerous approaches researched today.

One of these is the use of microwave treatment of the rocks prior to excavation / cutting. Rock absorbs the microwaves thus the electromagnetic energy is converted to heat, which leads to cracks and changes of the rock mass properties. Microwave treatment is proved to decrease the strength of rocks [1-3]. Research on various types of rocks was conducted [4], such as basalt [5], granite [6]. Experimental research as well as numerical approaches on the topic of microwave-induced fracturing of rocks was conducted by scholars worldwide [7-11] Microwave-assisted mechanical rock cutting is still in laboratory and experimental phases, with the proposed schema as shown in Figures 1 and 2.

Fig.1. Schematic diagram of microwave-assisted mechanical rock cutting [12]

Corresponding author: Andraș Andrei, assoc.prof. Ph.D. eng., University of Petrosani, Petrosani, Romania, (University of Petrosani, 20 University Street, andrei.andras@gmail.com) *

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Fig.2. Schematic view of the microwave heating system [13]

2. Experimental work carried out 2.1 Previous work conducted within the project In the precedent stages of the research, samples of carbonate rocks (Ruschița Marble, Bășchioi and Podeni limestone) were prepared for both UCS and BTS test as well as linear cutting tests both for abroad partners in the project as well as in-house testing at Petroșani. Their mineralogical, petrographic and physical mechanical characteristics were established using standard testing methods in the laboratories of University of Petroșani.

2.2 Test carried out within current stage of the project In the present stage, linear cutting tests were performed in the laboratory of the University of Petroșani, using rectangular samples from all three locations of sampling. The tests were performed using point attack bits (Figure 3), without microwave assistance, using an in-house force measurement solution developed using 1-D load cells (Figure 4), based on technology presented in [14].

Results from this testing will be compared to test carried out by consortium partners in the project in the next stage, as well as with results of numeric simulation to be carried out.

Fig.3. Point attack bits used

Fig.4. Measurement solution proposed [14]

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With this system, samples of marble and limestone were subjected to cuts at different depths of cut, and the tangential, normal and lateral components (Fx, Fy şi Fz) of the force were recorded. Fx is the tangential force and is acting in the direction of the pick movement, Fy, is the normal force, acting perpendicular to the cutting plane and Fz, is the lateral force, acting in a direction perpendicular to the first two.

To make an initial estimate of the cutting forces, the Evans [15] model of the tangential cutting force was used, according to the relation:

Ft 

16     rt 2  h0 2 cos( )2   rc

(1)

where: σrc is the uniaxial compressive strength, N / m2 σrt is the splitting tensile strength, by the Brazilian method, N / m2 h0 is the cutting depth, m  is the point attack pick angle.

The results obtained for values of cutting depth between 1 mm and 15 mm for the three types of rocks are presented in the Table 1.

Table 1. Cutting test results

Ft (kN)

h0 (mm)

Rușchița Marble

Bășchioi Limestone

Podeni Limestone

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0.086 0.342 0.77 1.369 2.14 3.081 4.193 5.477 6.932 8.558 10.355 12.324 14.463 16.774 19.256

0.091 0.363 0.816 1.451 2.267 3.264 4.443 5.803 7.344 9.067 10.971 13.057 15.323 17.772 20.401

0.024 0.094 0.213 0.378 0.59 0.85 1.157 1.511 1.913 2.361 2.857 3.4 3.99 4.628 5.313

The highlighted values in the Table, correspond to the depth of 10 mm (1 cm) and represent the average value of the specific cutting resistance, A, expressed in kN/cm.

Table 2. Specific cutting resistance obtained by regression formulae in [16] Rock type Marble Rușchița Limestone Bășchioi Limestone Podeni

σrc

σrt

(MPa) 86 77 16.3

(MPa) 9.57 9.35 2,2

A (kN/cm) 9.2 8.53 3.5

In order to stay under the value of force offered by the LCM (Ft <10kN), for the samples of Rușchița marble and Bașchioi limestone it was decided to limit the tests to the value h 0 of 1 cm, and for samples of Podeni limestone, to 1.5 cm.

There are empirical coefficients presented in literature for the correlation of the specific resistance A with σrc and σrt that are determined based on experimental tests.

Thus, in [16] for similar rocks and values of σrc and σrt, the values of 9.2, 8.53, respectively 3.5 kN/cm result for A, as presented in Table 2. The differences are due to the imperfection of the Evans model.

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3. Results and discussion The results of recorded measurements for all samples tested are presented in Figures 5 to 7.

Fig. 5. Recorded measurements Fx, Ruschita marble, h0=3mm

Fig. 6. Recorded measurements Fx, Bășchioi limestone, h0= 3 mm

Fig. 7. Recorded measurements Fx, Podeni limestone, h0= 5 mm

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The results were further processed statistically to highlight average measured values and the regression line.

Fig. 8. Average values obtained by measurement, and the regression line for Rușchița marble

Fig. 9. Average values obtained by measurement, and the regression line for Bășchioi limestone

Fig. 10. Average values obtained by measurement, and the regression line for Podeni limestone 54

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Based on the data obtained, the average values of specific cutting resistance and specific cutting energy consumption of the three rock types, summarized in the Table 3, were determined.

Rock type Marble Rușchița Limestone Bășchioi Limestone Podeni

Table 3. Average values determined Specific cutting Specific cutting energy resistance (kN/cm) kWh/m3 J/cm3

8,499 7,075 3,01

8,53 7,788 2,771

30,708 28,037 9,976

4. Conclusions On the basis of data for three types of rocks under study, using the inhouse built linear cutting system, the average values of cutting resistance and specific energy consumptions were determined.

The results are in line with literature, obtained for similar type of rocks, using similar or slightly different methods of measurement or / and estimation.

These are results of stage two of this research, and will serve as basis for comparison with values obtained

by Consortium partners, in their tests, and further interpretation for the development of the microwave assisted linear cutting machine of carbonate rocks.

Acknowledgements This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI - UEFISCDI, project number ERANET-ERAMIN-MIWACUT, within PNCDI III.

References [1] Lu G.M., Li Y.H., Hassani F., Zhang X.W., 2016 Review of theoretical and experimental studies on mechanical rock fragmentation using microwave-assisted approach.

Chinese Journal of Geotechnical Engineering, 38(8), pp. 1497-1506.

[2] Zheng Y.L., Ma Z.J., Zhao X.B., He L., 2020 Experimental investigation on the thermal, mechanical and cracking behaviours of three Igneous rocks under microwave treatment. Journal of Rock Mechanics and Rock Engineering.

[3] Hassani F., Nekoovaght P.M., Gharib N., 2016 The influence of microwave irradiation on rocks for microwave-assisted underground excavation. Journal of Rock Mechanics and Geotechnical Engineering, 8(1), pp. 1-15.

[4] Santamarina, J.C. (ed.), 1989 Rock excavation with microwaves: a literature review, Evanston, IL (etc.): Publ by ASCE. [5] Hartlieb P., Leindl M., Kuchar F., Antretter T., Moser P., 2012 Damage of basalt induced by microwave irradiation. Special Issue - Physical Separation, Minerals Engineering, 31, pp.

82–89.

[6] Toifl M., Hartlieb P., Meisels R., Antretter T., Kuchar F., 2017 Numerical study of the influence of irradiation parameters on the microwave-induced stresses in granite. Minerals Engineering, 103-104(4), pp. 78-92.

[7] Hassani F., Nekoovaght P.M., Radziszewski P., Waters K.E., 2011 Microwave assisted mechanical rock breaking. Proceedings of the 12th ISRM International Congress on Rock Mechanics, Beijing: International Society for Rock Mechanics, pp. 2075-2080.

[8] Ali A.Y., Bradshaw S.M., 2011 Confined particle bed breakage of microwave treated and untreated ores. Minerals Engineering, 24(14), pp. 1625-1630.

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[9] Lu G.M., 2018 Experimental study on the microwave fracturing of hard rock. Thesis, Northeastern University.

[10] Kahraman S., Canpolat A.N., Fener M., 2020 The influence of microwave treatment on the compressive and tensile strength of igneous rocks. International Journal of Rock Mechanics and Mining Sciences, 129, 104303.

[11] Kahraman S., Canpolat A.N., Fener M., Kilic C.O., 2020 The assessment of the factors affecting the microwave heating of magmatic rocks. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 6(4), pp. 1-16.

[12] Lindroth D.P., Morrell R.J., Blair J.R., 1991 Microwave assisted hard rock cutting. US5003144 Patent.

[13] Lu G., Zhou J., 2021 Experimental Investigation on the Effect of Microwave Heating on Rock Cracking and Their Mechanical Properties, Microwave Heating - Electromagnetic Fields Causing Thermal and Non-Thermal Effects. Gennadiy I. Churyumov, IntechOpen, DOI: 10.5772/intechopen.95436. Available from: https://www.intechopen.com/chapters/75087 [14] Kang H., Cho J.W., Park J.Y., Jang J.S., Kim J.H., Kim K.W., Rostami, J., Lee, J.W. 2016.

A new linear cutting machine for assessing the rock-cutting performance of a pick cutter. International Journal of Rock Mechanics and Mining Sciences, 88, pp. 129–136. DOI:10.1016/j.ijrmms.2016.07.021.

[15] Evans A., 1984 Theory of the cutting force for point attack picks. International Journal of Mining Engineering, 2(1), pp. 63-71.

[16] Bilgin N., Demircin M.A., Copur H., Balci C., Tuncdemir H., Akcin N., 2006 Dominant rock properties affecting the performance of conical picks and the comparison of some experimental and theoretical results, International Journal of Rock Mechanics & Mining Sciences, 43, pp. 139–156.

This article is an open access article distributed under the Creative Commons BY SA 4.0 license. Authors retain all copyrights and agree to the terms of the above-mentioned CC BY SA 4.0 license.

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CONSIDERATIONS REGARDING THE CLOSURE OF THE MINES IN VALEA JIULUI Liliana ROMAN1* 1

University of Petroșani, Petroșani, Romania e-mail lilianaaprilie40@yahoo.com

DOI: 10.2478/minrv-2021-0035 Keywords: mining, closure, Valea Jiului Abstract: The paper, starting from a series of general considerations regarding the closure of a mine, makes an analysis, according to the available data, of the manner some of the mines in the Valea Jiului were closed.

It is specified that the relatively short time since the closure of the first mine in the Valea Jiului (30 years) did not allow to highlight any mistakes / errors of closure, which would have significant repercussions on the surface land and, in general, on the environment. However, more or less serious problems have already been reported, which arose after the closure of some mines, problems that appear in the last part of this paper.

1. Introduction Romania has undergone an extensive industrial restructuring in the last 30 years, including the decrease of domestic production and the operational closure of most mines, which led to job losses, generated economicsocial and environmental effects that severely affected the quality. the lives of the inhabitants of the communities in the mining areas.

The paper refers to the situation of mining in Valea Jiului in the context of closing some mining perimeters in this area.

In 1989, there were 15 mining operations in Valea Jiului, which annually exploited 11 million tons of coal with a volume of 1,500,000 m3 of tailings, and underground mining works (wells, galleries, inclined planes, suites, preparation works, investment works, aeration and felling works), totaled thousands of kilometers. The staff employed in the 15 farms was about 55,000 people [3].

Today, within the Hunedoara Energy Complex, there are still 2 mining operations (Livezeni and Vulcan) with a production of approx. 450,000 t/year. The mines closed as follows: Iscroni mine - 1990, Lonea Pilier mine - 1994, Câmpu lui Neag mine - 1999, Petrila Sud mine - 1999, Dâlja mine - 2001, Valea de Brazi mine 2004, Aninoasa mine - 2006, Bărbăteni mine - 2007, Petrila mine-2015, Paroșeni and Uricani mines- 2017, Lonea and Lupeni mines (in the process of closing) - 2022, and the employed staff is approx. 4000 people. To these is added the closure of quarries and micro-quarries (Câmpu lui Neag, Jieț a.o.) [2].

The paper, based on a series of general considerations regarding the closure of a mine, presents the criteria on the basis of which the decision to close the mines in the Valea Jiului was made and according to the procedures for closing the mines makes an analysis, as far as available, they closed some of the mines in Valea Jiului.

The methods and technologies for closing a mine are also presented.

It should be noted that the relatively short time since the closure of the first mine in Valea Jiului (30 years) did not allow to highlight any errors / errors of closure, which would have significant repercussions on land and in general on the environment.

However, more or less serious problems have already been reported, which arose after the closure of some mines, problems that I will present in the last chapter of this paper.

Corresponding author: Roman Liliana, Ph. D. student. eng. University of Petroșani, Petroșani, Romania (University of Petroșani str. Universitatii no.20, 332006 Petroșani, e-mail: lilianaaprilie40@yahoo.com) *

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2. General considerations on mine closure 2.1. Legal and institutional framework for mine closure

By Government Ordinance no. 11 of January 24, 2000, the Loan Agreement between Romania and the International Bank for Reconstruction and Development on the financing of the Mine Closure and Social Impact Mitigation Project, amounting to $ 44.5 million, was ratified. The project was constituted by a first support, granted by the World Bank, for the restructuring of the mining sector in Romania and was developed as a pilot project, aiming at improving the institutions and completing the necessary procedural regulations to address them, in an extended framework of the problems of restructuring the mining sector, in correlation with the diminishing social impact resulting from the restructuring.

The implementation of the agreement was carried out by the Project Management Union (PMU), established within the Ministry of Economy and the Project Implementation Unit (PIU), set up at the level of entities, with responsibilities in carrying out the loan [9]. The Project Management Unit proposed and promoted over 70 legislative acts, specific to extractive activities, mine closure and social protection.

The main directions of action of the PMU, for the mine closure component, are [10]: • Ensuring the legal framework for project management and implementation; • The institutional framework for carrying out the activity of closing and greening the mines.

For the coordination of the operative activities, S.C. CONVERSMIN S.A. was established. It acts for and on behalf of the Ministry of Economy in the sense of managing the annual funds allocated from the state budget, for contracting the execution of mine closure works.

Starting with the year 2000, some mines were preserved and then closed permanently. This category included some objectives for which the expenses exceeded more than the revenues and for the maintenance of which it was necessary to allocate important public funds, but also those for which the geological reserves or geological research works were exhausted no longer justifies the continuation of the activity.

2.2. Criteria underlying the closure of the mines In the following, three criteria will be briefly presented, which were the basis for the decision to close the mines in the Valea Jiului without detailing them, because they are not the express object of this article.

The decision to close a mining objective will be required following a complex analysis of the factors that influence its efficiency and which can be grouped into: natural and constructive factors; economic factors; socio-political factors.

Following such analyzes, several categories of units can be established: profitable (class I); attractive to the requirements of the reform (class II); with an average degree of attractiveness (class III); with a low degree of attractiveness (class IV) and unattractive units (class V) [1,4,7,9].

2.2.1. The economic criterion This complex criterion takes into account: the need for useful minerals, selling prices, the level of costs for obtaining minerals, the volume of equipment needed for refurbishment, the costs of closing mines, the costs of measures to ensure social protection of workers removed from the process of production. In order to solve the problem, there is a need to carry out a complex study, being completed several stages [4].

Under market economy conditions, the ratio I between the unit cost of production of CP and the selling or selling price of CV will be taken into account. If I  1 mines are profitable (class I), for I > 1 (classes IIV) the mines are unprofitable, the degree of unprofitable, increasing as the class increases.

2.2.2. The integrative criterion For a more realistic assessment of each operation, criterion [4] proposes the comparative analysis of a set of technical and economic indicators, namely: extracted physical production, average number of staff, physical labor productivity, open reserve, prepared reserve, exploitable reserve, the degree of mechanization, the unit cost and the expenses per 1000 lei production of goods to which a score is awarded, so that by summing up the points obtained a hierarchy of mining units can be made according to which a correct decision can be made regarding the mine will enter the conservation/closure process.

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2.2.3. The criterion of points The method has the advantage of sufficient flexibility, as well as the speed with which the ranking of companies is determined, from a financial point of view [4].

The technical-economic indicators taken into account are: recalculated extracted production, extracted physical production, total gross loss, unit cost of production, total expenses per 1000 lei of goods production, material expenses per 1000 lei of goods production, physical labor productivity, price of settlement.

It is considered that mining units whose total scores exceed 100 are viable, and those below this threshold will fall into the category of non-viable. And in this case, the entry into the conservation/closure process will be done gradually, starting with the mining unit, which holds the last place in the hierarchy.

2.3. Procedures for closing a mine When closing a mine, the following four stages/phases must be completed [1]:  Stage/phase I includes: - the initiative to cease operating; - elaboration of the Activity Cessation Plan (PIA), obtaining the fundamental approvals and submitting for approval; - the taking over by the Central Mining Authority (through the Mine Closures Directorate-D.Î.M.) from the licensee of the objectives in order to capitalize on them.  Stage/phase II includes: - elaboration of the Technical Closing Project (PT), of the specifications and of the tender documentation, obtaining the approvals and submitting for approval.  Stage/phase III includes: - implementation of the Technical Closing Project; - monitoring the closure of the operation and the reception of the works; - handing over the available land to the forestry or agricultural directorate.  Stage/phase IV includes: - monitoring the objectives that maintain their functionality after the closure of the operation as well as their maintenance and operation.

The Activity Cessation Plan (PIA) is the one that provides the details of the actions necessary for the effective implementation of the mine closure measures. It must include the following activities [10]: motivation for cessation of activity; the technical program for decommissioning or conservation of the operation, which will also include the program for monitoring the post-closure environmental factors; the social protection program for staff through redeployment and / or professional retraining, financial compensation and / or regional development measures, for the creation of new jobs; the water management permit and the environmental permit, for closure; decommissioning and land clearance procedure.

The Technical Closing Project (PT) for mine closure and environmental restoration is a detailed plan, which evaluates the actions and measures provided by the mine closure procedures, both from a technical point of view, including the necessary works, physical closure of the mine and restoration of the affected environment, with reference to information on the mine subject to closure and shall be approved by order of the relevant ministry. It will be accompanied by the social protection plan, in consultation with the Community consortium.

2.4. Methods and technologies for closing a mine The closure of a mine will be based on a technical project that will include [1]:  Technical solutions for closing the mining works related to the surface;  The way of closing the mouth of the mining works related to the surface;  Technical solutions for closing underground mining works;  Technical solutions for closing the abattoirs;  Carrying out the general and partial ventilation during the closing period;  Recovery of the technical-productive infrastructure of the mines in liquidation;  Valorization or demolition of constructions and other surface objectives;  Post-closure monitoring of underground and surface insulation mining constructions;  Greening of land areas affected by mining.

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3. Closure of the mines in the Valea Jiului 3.1. Evaluation of the mines in Valea Jiului according to the closure criteria Valea Jiului is the only mining basin in Romania where a coal mine is currently exploited, which has important balance reserves, which can ensure the requirements of the beneficiaries (CET Paroșeni and MintiaDeva), for a period of several decades. The mines from Valea Jiului (fig.1), with a traditional activity in coal extraction, have the most qualified personnel and an adequate infrastructure, both for the actual extraction and for the transport to the beneficiaries.

At the same time, however, the complicated tectonics of the deposit makes this deposit one of the most complex coal deposits in the world and very difficult to exploit through the methods and technologies widely used worldwide. Therefore, the mining activities in the mining basin of Valea Jiului are at an impasse from which it could emerge, not only through technical-organizational measures but also through responsible political decisions.

Figure 1. Mining perimeters in Valea Jiului mining basin [11]

After 1989, when the created situation imposed the support of the mining sector by the state with a great budgetary effort, the non-stop decline of mining in Valea Jiului begins.

There are several key benchmarks in its decline, caused in particular by the so-called restructuring programs (especially those from 1997 to 2000): mass redundancies; high compensatory payments for redundant staff; dramatic increase in production costs; the drastic decrease of investments by approx. 20 times the value of those before 1989. All this led to a decrease in the production extracted (by 41%), the number of employees (by 60%), the fluctuation of production costs and, in particular, the total neglect of refurbishment and modernization of all technological processes in the underground and on the surface of a mine.

Thus, after a century of efficiency and half a century of investments materialized in an extensive development, which led to the formation of a first-class mining basin, we are witnessing today, after three decades, a sad end of a mining characterized by inefficiency, rapidly declining production, risks and uncertainties for those still working underground.

After 1990, it is difficult to talk about investments in the mining of Valea Jiului in the absence of a future energy strategy, indiscipline in work and management of the Coal Company, to which are added more general causes such as the strategy to reduce emissions. carbon dioxide, lower economic efficiency of coal based energy, the development of unconventional energy sources less polluting and why not and the detonation of the social bomb represented by the nearly 60,000 employees concentrated in a relatively small area such as Valea Jiului.

A first ranking of the 10 mines in Valea Jiului remaining in operation in 2001, based on scientific criteria, was made in 2002 applying the technical-economic indicators achieved at the end of 2001.

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Table 1 summarizes the hierarchy of the 10 mining operations in Valea Jiului, which were operating at that time, ranking obtained according to the three criteria presented in §2.2.

Table 1. Hierarchy of mines in Valea Jiului according to evaluation criteria

No. crt.

1 2 3 4 5 6 7 8 9 10

Mine Valea de Brazi Uricani Bărbăteni Lupeni Paroșeni Vulcan Aninoasa Livezeni Petrila Lonea

Criteria for evaluating the conservation-closure Economic Class Integrator Score Points Score V III IV IV IV IV V IV IV III

54 89 54 85 64 73 45 82 66 74

108.3 120.4 89.7 116.2 95.5 103.4 56.9 101.0 104.9 103.7

It should be noted that the ranking of these mines was based on the detailed technical and economic indicators presented in works [1,4].

Analysing table 1 we find the following: • According to the economic criterion, it appears that no mining unit in the Valea Jiului was, at that time, in classes I and II, most belonging to classes III (2), IV (6) and V (2), i.e. units with grade medium of attractiveness, low degree of attractiveness and respectively unattractive.

• According to the integrative criterion, considering the viability threshold of 58 points, corresponding to average values of the indicators evaluated, three mines Valea de Brazi, Bărbăteni and Aninoasa were below this threshold, being considered non-viable.

• According to the points criterion, three mines, Bărbăteni, Paroșeni and Aninoasa were located below the threshold of 100.

Following these assessments, the decision was made to declare the Valea de Brazi, Bărbăteni and Aninoasa mines unviable and to enter the closure process. At the time of the cessation of state subsidies, in 2011, 7 mines were in operation in Valea Jiului: Lonea, Petrila, Livezeni, Vulcan, Paroșeni, Lupeni and Uricani.

Also now, a new evaluation will be made at the level of CNH-SA Petroșani from a technical, economic and social point of view to decide which of the seven mines will survive economically without social assistance.

Following such an analysis, two categories of units were established: non-viable (which must enter the closure process) and viable (those that will continue their activity). The analysis was based on the projection of the following technical and economic indicators for the period 2011-2018.

The scores obtained by the seven mining operations, analysed and then in operation are shown in table 2 [5].

Table 2. Scores obtained from mines

No. crt.

1 2 3 4 5 6 7

Mine Lonea Petrila Livezeni Vulcan Paroșeni Lupeni Uricani

Technical score

Economic score

TOTAL

50.6 16.5 55.0 41.6 20.8 49.1 21.4

46.6 17.3 53.8 58.9 40.7 49.8 22.8

99.2 33.8 108.8 100.5 61.5 98.9 44.2

It is observed that the Petrila, Paroșeni and Uricani mines (marked in red), obtained the lowest scores and were declared unviable, entering the closing process (2011-2017).

In 2012, the Valea Jiului National Mine Closure Company (SNIMVJ) was established, which took over all the mines in different stages of cessation of activities (conservation closure).

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Between 2011 and 2015 there were four viable mines in Valea Jiului: Lonea, Livezeni, Vulcan and Lupeni. The analysis of viable mines stopped until the end of 2015, when based on Feasibility Studies, developed by the University of Petroșani (for the Lonea mine) and S.C. Universal Cerc Project SRL (for the Livezeni, Vulcan and Lupeni mines), solutions were presented to continue the activities at these mines, with the acceptance of appropriate investments.

Following these studies, but also due to their uncertain state from 2016-2017, as CEH- Hunedoara (CEHSA Petroșani) enters or leaves insolvency, the Romanian Government adopted (November 2016) a memorandum on increasing aid state granted to the National Society of Mine Closures Valea Jiului (SNIMVJ), with 129.129 million lei (approx. 28.7 million euros), for the inclusion in the closure program (until the end of 2018), of two mines, which were considered non-viable: Lonea and Lupeni [3].

So, at present, there are only two viable mines in Valea Jiului: Livezeni and Vulcan.

3.2. Brief presentation of the mines closed or in the process of closing In the following, based on the Activity Cessation Plans (PIA) and Technical Closing Projects (PT) available, there will be a brief presentation of how it was done or the closure of seven of the 13 mines that have been ceased activity after 1990 [12, 14].

3.2.1. Uricani mine The motivation for closing the mine was that the activity of exploiting the deposit within it becomes economically unprofitable and the confirmation of reserves is uncertain.

The coal deposit from the Uricani perimeter is located at relatively large depths (over 400 m), located in complex geological and tectonic conditions, which make it difficult to track and exploit useful seams, adding to them the tendency to self-ignite coal and the possibility of forming atmospheres. potentially explosive consisting of mixtures of flammable ground gases and air.

In this perimeter, the object of exploitation was seams 3-5, 8-9 and 14-17.

The activity of coal extraction from the underground of the Uricani mine stopped in 2017, after which the exploitation entered the established greening and closure program, according to the notifications sent to the European Commission. In 2018-2019, the recovery and removal of equipment that is underground and can be recovered continued. In the following years, 2019-2020, the coal deposit was secured, the waters in the galleries were drained, the main fan station was stopped and the wells were closed and the underground connections to the surface were closed. Greening of surface land began in 2020.

Starting from the requirements of the integral and efficient use of the territory and taking into account the fundamental principles of ecological rehabilitation, the specialists together with the representatives of the local community, decided to restore the lands mainly in the agricultural circuit.

The return to the economic circuit of the lands degraded by the mine activity requires the redevelopment and modeling of the surfaces and then their recultivation.

The Uricani mine carried out its activity in several premises: the main enclosure, the explosive depot, the tailings dump, the east aerial well enclosure, the western aeration well enclosure, the Sterminos enclosure and the capture from the Sterminos well and the Valea de Brazi enclosure. not recoverable).

The decommissioning-demolition of all the objects within these enclosures was carried out according to a methodology presented schematically in figure 2, and in figure 3 are presented some constructions in different phases of deactivation-demolition.

As the remediation and intervention works provided at the mining premises are completed, the land related to them will be subjected to modeling and geometrization works to ensure their integration into the local landscape and the optimal drainage of water from precipitation.

The closure of the underground mining works at the Uricani mine was carried out in stages, respecting the principle that they be made in retreat from the limits of the development-exploitation field, to the main aeration circuits under the general depression of the mine, including to the surface connections.

The method used to close the exploited spaces, in order to prevent and combat mine fires, was the siltation (the necessary ash / water ratio is made at the siltation station and can vary from 1:1 to 1:12, depending on a series of technological factors).

Due to the relatively large depth of exploitation as well as the surface morphology of the land (mountainous area), in the case of the Uricani mine, the manifestation of the mining subsidence phenomenon has not been found so far.

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Sale of roofing, carpentry, attics, finishing elements

Material sorting and storage

Demolition of the elements closure and compartmentalization

Material sorting and storage

Demolition of reinforced concrete resistance structures and dismantling of metal resistance structures

Material sorting and storage

Excavation of foundations, manholes basins, sewers and pipes

Material sorting and storage

Sale wear layer and resistance to roads and alleys

Material sorting and storage

Execution of earth fillings

Compaction and leveling of fillings

Transport

Transport

Transport

Transport

Transport

Transport

Transport

Spreading and leveling topsoil

Lawn sowing Figure 2. Logic scheme for demolition and site rehabilitation [12]

Figure 3. Some constructions from mine yard that is being demolished [12]

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However, the mining activity carried out within the Uricani mining perimeter caused a series of negative effects on the land area related to it, such as: - the modification of the relief during the construction of the enclosure and the systematic influence of the flora and fauna of the area; - reduction of agricultural and forestry areas, by occupying them with the objects of mining; - modification of natural hydrogeological conditions due to the needs of underground exploitation; - changes to the infrastructure from a technical and social point of view; - environmental pollution, both through coal mining and related processing industries 3.2.2. Lupeni mine [8] It is the perimeter with the largest mining operation in the basin. The deposit, due to the morphology of the foundation formations, is higher than in the adjacent areas. In general, the syncline structure with the more developed northern flank is maintained. Due to a fault system (generally oriented north-south), the deposit is compartmentalized into tectonic blocks. In the Lupeni mining perimeter are found all the layers 3-18, economic importance presenting the seams 3,4,5,8,9,13,14,15 (which are the object of exploitation).

Lupeni mine is one of the oldest mining operations in Valea Jiului mining basin, with an extensive mining structure on several levels of exploitation (horizons), with several enclosures, which have lost their usefulness as the depth increases. coal mining.

The mine is currently in the process of closing/preserving.

The underground exploitation of the coal seams from the Lupeni mining field had and still has major implications in terms of the stability of the land, but also of the surface constructions. Most of the affected buildings (residential houses) are on one level, made of brick walls, on monolithic concrete or river stone foundations and are over 50 years old.

Due to the differentiated displacements of the surface, generated by the underground exploitation, the movement propagated through the foundation of the buildings, to their superstructure, initially causing traction and shear cracks, which gradually progressed over time until the structural elements are completely decomposed.

Starting with 2008, in the perimeter of block V, from the Lupeni mine, three pits appeared successively on the surface of the current land, in the areas of influence of panels P6/I, P9, P7 and P10, atypical for the geomining conditions in Valea Jiului [9] 3.2.3. Paroşeni mine [12] The Paroșeni mine has been operating for 51 years. The opening and preparation works began in 1963, but the operation of the first coal wagon was completed on October 7, 1966.

The perimeter of the mine is between the perimeters of Lupeni, to the west, and Vulcan, to the east, in an area where the deposits of horizon 3 are heavily eroded. The deposit is strongly tectonized, an important transverse fault, located on Valea Lupului, separating the western domain of the basin from the eastern one. In the perimeter were found all the known layers of the basin, economic importance presenting the seams 3, 5, 8, 9, 13, 14, 15, 18. Qualitatively, the coal mined in the perimeter is an energetic one.

The Paroșeni mine was closed at the end of 2017, after more than half a century of operation, during which time, 27 million tons of coal were extracted from its depths. Starting with January 1, 2020, the surface demolition and closure of underground spaces began, the operation entering the process of closure and greening. This means that all underground activities will be completed, all underground access roads will be closed and all surface buildings will be demolished.

Figure 4 shows some constructions that are being demolished from the Paroșeni mine.

All surface constructions that lose their utility once the mine is closed have been provided for decommissioning and demolition, and the land released from the constructions will be returned to the economic circuit (table 3).

In order to protect the deposit, isolation works were carried out on the mining access works to the abatements, which were dammed with insulation dams to prevent endogenous fires.

The operations of closing the underground mining works were carried out in the period 2011 ÷ 2018, annually, in eight stages, considering the production staggering until 2017 inclusive.

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1

2

3

4

Figure 4. Some constructions from mine yard that is being demolished [11] 1-Raise South fan station; 2- Ventilation ducts precinct Plan 23; 3- Fan station no.1 precinct Plan 23; 4- Fan station precinct Plan 23 Table 3. Compliance program for the greening of the Paroseni mine [12] No. Environmental component/ Measures Steps crt.

Polluting factor SOIL Recovery of occupied lands, Precinct arrangement.

1 A. Precinct (Ventilation Raise ecological reconstruction - decommissioning/demolition of objects intended for South, Ventilation Plan 23) and prevention of this purpose; environmental damage - land clearing of reusable materials and dumping of nonbiodegradable materials; Dump recovery and its - leveling the lands with a slope imposed by the land B. Dump Tericon return to the economic configuration; level 630 circuit - biological recultivation of land with adequate vegetation Dump arrangement - cleaning the dump of non-biodegradable materials; - leveling the dump with an imposed slope; - weeding the dump WATERS Directing rainwater to guard Periodic clearing of existing guard channels 2 Rainwater

3

AIR Dust emissions

Noise

4

Monitoring all environmental components: soil, water, air

channels Reduction of air pollution

Application of solutions to limit dust emissions in the conditions of exceeding the allowed norms: - demolition; - for transport.

Reduction of noise pollution Application of soundproofing solutions for machines in function of generating noise above the allowed norms.

-land tracking and its analysis; -monitoring water quality (surface and groundwater); -monitoring air quality; -monitoring the development of sowings; -following the stability of the lands by topographic measurements made by tracking alignments; -periodic clearing of existing guard channels.

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3.2.4. Aninoasa mine [12] The decision to close the mine was taken because the operation became economically unprofitable, making in 2001 expenses of over 4000 lei per 1000 lei for goods production. Also, due to the non-completion of the opening works due to the limited funding funds and the delay of the preparation works, they led to the impossibility of maintaining the front line. As a result, the exploitable reserve is depleted to the basic horizon.

XII (quota + 50).

When drawing up the cessation plan for the Aninoasa mine, the progressive cessation of the mine exploitation activity was taken into account as the prepared reserves were exhausted.

The coal seams, with an east-west direction, have large slopes. The deposit is strongly tectonized, in the northern flank the faults being intercepted by mining works. The coal seams encountered, 2-19, have different thicknesses and areas of spread. The seams 3, 5, 7, 13, 15, 18 are of economic importance. The energy coal exploited in this perimeter is superior in quality to the other perimeters in the basin (lower calorific value of 5,500 kcal/kg).

In order to protect the deposit, siltation works were carried out (in the amount of 5,150 m3), and the mining works for access to the abatements were dammed with isolation dams to prevent endogenous fires. Also, the networks of mining works related to the coal mining were isolated, with dikes built with prefabricated blocks.

These insulating mining constructions were executed in accordance with the “Technical Prescriptions” (PT C 33) at NSPM - ed. 1997.

The closure of the mining works related to the surface (4 shafts, 2 raises) respectively Shaft 1 Piscu, Main North, Main South and Auxiliary and the ventilation raises Parc and Piscu was done by backfilling and construction on their mouths of concrete slabs dimensioned to withstand a load of 32 kN/m2. The horizontal mining works with a cover of less than 50 m were also closed by backfilling, and their mouths with concrete dikes. On surface no observed changes in the terrain caused by underground exploitation.

3.2.5. Dâlja mine [12] The extractive activity at the Dâlja mine was stopped in 1999, and the mine came into conservation in 2004. In 2005, the works of closing and greening the area began. According to official data, 11 billion lei were allocated and spent for the underground part in order to close the galleries, while for the surface, the amount initially allocated was 82 billion lei, but the organized tender in this regard was won by S.C. IMI. S.A. Baia Mare, for 56 billion lei. Instead of the mining subunit, grass was planted and only two other buildings bear witness to the fact that there was once a coal mine.

3.2.6. Petrila mine [12] The decision to draw up the Activity Cessation Plan of the Petrila mine activity was taken in accordance with article 37 of the Mining Law no. 61/1998 on the basis of the cumulative and partial meeting of the criteria: a) depletion of reserves in some areas; b) the continuation of the operation has become impossible due to endogenous fires - whose effects cannot be removed by technical interventions in economic conditions, in other areas.

In order to protect the deposit, the mining works for access to the abatements were dammed with doublerow isolation dams of vaults (6 pcs. in GDM-10.0 profile) to prevent endogenous fires.

During the period of accomplishment of the works and operations of conservation of the mine, the constructions and installations that serve the transport of personnel and materials, aeration, water evacuation, were kept in operation.

Also, during the period of the mine conservation works and operations, the electricity and thermal energy supply installations, the underground gas emission measurement installations, the pumping stations for water evacuation, as well as the operation were maintained. and drinking and industrial water supply installations.

After the completion of the conservation works, the actual closure of the Petrila mine took place.

In order to protect the deposit and the surface, the phased closure of the underground mining works in retreat was carried out, from the limit of the extraction field to the aeration circuits under the general depression of the mine, respectively to the surface connections by leaving them in the state find out the insulation with built dams, built according to the technical prescriptions in force or concreted (for retaining the embankment in the ramps of the wells and suites) whose constructive characteristics are determined by the calculation of the pressure resistance of the embankment column.

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The closure of the mining works related to the surface (3 shaft, 1 raise) respectively Shaft 3 East, Shaft 1 East, Shaft 2 East and Central Raise was done by filling and construction on their mouth of 10 concrete slabs (PB-5; PB- 4; SB-3,1) dimensioned to withstand a load of 32 kN/m2.

The horizontal mining works with a cover of less than 50 m were also closed by filling, and their mouths with concrete dikes.

The surface works for the closure of the Petrila mine provided for the decommissioning and demolition of all the existing buildings and constructions in the 4 precincts of the mine: Shaft 1 East Precinct, Shaft 2 East Precinct, Shaft 3 East Precinct and Central Raise Precinct.

The total closure of the Petrila mine will have positive effects on the environment regarding the environmental components: soil, water, air because the sources of pollution in this area (eg. wastewater from the mine) will disappear.

The dumps related to the mine will be grassed, forested and returned to the economic circuit.

Currently, there are changes in land area caused by underground exploitation in the eastern part of the development-exploitation perimeter.

In order to monitor possible deformations of the land surface caused by underground works, topographic measurements must be performed on well-established alignments.

3.2.7. Lonea mine [12] Lonea mine is in the process of closing/preserving.

The closure works of the Lonea mine consist in the execution of the necessary works for ecological reconstruction and prevention of environmental damage.

The execution of ecological reconstruction works will have positive effects on environmental factors, as well as for the protection of human settlements.

Ecological reconstruction works are required due to the current situation of the mine.

The greening works provided in the documentation are the following.

- in the eastern part of the lake (from the former Jieț open pit), at the base of the slope of the dump near the Jieț brook, gabions will be made in order to protect the dump on a length of 400 m; - anti-erosion fences will be made on a length of 400 m.

For the restoration in the economic circuit of the lands occupied by the Lonea mine, cleaning, sowing and afforestation works will be carried out.

The sowing works will be carried out on an area of 4000m2.

The afforestation works will be carried out on the slopes of the dump, thus preventing possible landslides.

The afforestation will be done on an area of 4000m2.

- works will be carried out to unclog the existing collecting channels on a length of 600m.

- an extension of the existing collector channel will be executed on a length of 50m, until the connection with the existing manhole.

- a stone support of the slope (on both sides) of the access road to Jieț will be executed, on a length of 300 m on both sides of the road.

The closure of the objectives at the surface of the Lonea mine will have positive effects on the environment regarding the environmental components, by ceasing the industrial activities from these objectives.

In order to collect the rainwater that drains on the slopes of the road, the existing collecting canals will be unclogged and a new one will be built on a length of 50m, in order to take over the rainwater from the area.

For a good stability of the dumps, afforestation works will be carried out, thus preventing possible landslides.

The compliance program is shown in table 4.

Recently, specialists have found the aggravation of the phenomenon of subsidence-surface deformations, caused by the underground exploitation of coal.

4. Analysis of the closure of the mines in Valea Jiului A complete analysis, at this date, of the state of the mining perimeters in the Valea Jiului that have closed or are in the process of conservation-closure is difficult to perform for several reasons [6]: - relatively short duration of mine closure (max. 20 years). Experience in Romania and internationally has shown that the deformation of the surface, resulting from the underground exploitation of coal seams usually occurs after 35-40 years from the cessation of exploitation; 67

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Table 4. Compliance program for the greening of the Lonea mine site [12]

No. Environmental component/ crt.

Polluting factor

Measures

Steps Ecological reconstruction works consist of: - land clearing, S = 0.4ha; - land leveling; - dump grass, S = 0.4ha; - dump afforestation, S = 0.4ha; - execution of anti-erosion fences – 400m.

Application of soundproofing solutions for machines, depending on the noise generators above the allowed norms.

For the collection of rainwater, a collecting channel with a length of 50m will be executed; Clogging of existing channels.

- monitoring the technical condition of collecting channels; - periodic monitoring of the quality of the collected waters; - soil quality monitoring: fertility, chemical composition, physical structure.

1

SOIL Precincts and dumps

Ecological reconstruction and prevention of environmental damage

2

AIR Dust emissions WATER

Reducing air pollution Rainwater collection

3

4

Monitoring all environmental components: soil, water, air

- the information provided by the Geo-Topo services from me is not always edifying, the topographic measurements in the field are often made only when dangerous geomechanical phenomena occur; - there is no database containing the situation of the exploitation of coal seams in all mining perimeters; - there is no systematic monitoring of the land surface from the perimeters exploited by topographic measurements, laser scanners, photogrammetry, e.a.

- a private person, be it a doctoral student, obtains with difficulty or not at all information related to the state of closed mining perimeters, personal observations in the field can often be expressed quantitatively in order to draw accurate scientific conclusions.

However, an analysis of the underground structure of the mines in Valea Jiului may anticipate the occurrence of post-closure phenomena caused by a number of synergistic factors [12]: a) the not very great depth of location of the underground excavations (below 242-275m); b) the movement of large volumes of rocks from the roof, following the exploitation with a mined coal bank, a method of exploitation almost generalized, at present, at the mines in the Valea Jiului (over 10-35m); c) the movement of rock masses according to the fault planes (reactivation of faults), determined by the approach of the panels in operation; d) concentration of stresses on the corners of the pillars. e) uncontrolled surface releases of methane from closed mines can be sources of air pollution in the area; f) uncollected mine waters are a source of pollution of the surface and / or groundwater.

It must be said that in Valea Jiului, wherever the conditions synthesized above are established, baskets/ potholes or other geomechanical phenomena can appear.

In the period 1996-2020, very few controls were carried out by the bodies authorized to verify the manner in which the conservation-closure and greening works of the lands released from constructions were carried out.

Thus, under the control of the Ministry of Environment, Waters and Forests in 2006, [14] to verify the manner in which the Câmpu lui Neag and Petrila Sud Mines were closed, many problems were found in the Mine Closure Report.

After the closure of these mines, in a short period of time, dynamic phenomena appeared on the surface (landslides, surface collapses with crater formation, cracks), which is explained in the Mine Closure Report of the Ministry of Environment and Water Management, National Environmental Guard, General Commissariat.

Following the control carried out in 2006 on closed mining objectives until 2001, it was found that, after the reception at the end of the works, in the perimeters verified by sampling, the process of closing the mines (which includes the phases of design, approval, execution, reception at completion of works, final reception and post-closure monitoring) is inadequate.

Representatives of the Local Public Administrations and of the community did not participate in the realization of the Mining Cessation Projects and the Technical Projects for Closing the mining operations in Valea Jiului. The consultation with the local public administrations was made and is done only when certain surface constructions, lands, sterile dumps, etc. are handed over. City halls have no expertise to study the technical execution project for mine closure and analysis of the influence of the closure method for everything on the surface: buildings, public spaces, infrastructure, pasture, water, etc. [14].

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If each City Hall had knowledgeable specialists in mining activities (mining engineers, surveying engineers and construction engineers) things would be completely different. The approval of the City Hall for the acceptance of the Technical Project for closing the mine would be based on a special consultation with additional additions necessary to protect surface constructions, delimitation of dangerous perimeters and their monitoring, execution of consolidation works (retaining walls, drilling and injections for stabilization of dangerous areas for landslides, etc.).

There are many examples of mine closures, where, during or after the short monitoring period, dynamic effects appeared that endangered and endangered the households and lands of the inhabitants of Valea Jiului.

These are technical issues that raise questions, including: • Criteria for establishing the cessation of production activity.

• The period between the last day of production and the completion of the technical closure project is extremely short (1 year) and does not reflect the time required for: recovery of equipment and materials in accordance with the inventory of that time; execution of technical works for the closure of underground works; no backfilling works are carried out on the mine galleries, adjacent to the protection pillars of the populated areas, of the traffic routes, of the watercourses, of other surface objectives.

• The buildings that represent industrial historical monuments are not treated in a separate chapter, an aspect that generated a lot of controversy in the case of the demolition of some buildings inside the former Petrila mine, between the Ministry of Culture and the Ministry of Energy.

• The fact that in any of the 9 (nine) mining premises closed between 1994 and 2016, no museum of coal mining in the Valea Jiului was built, remains a mystery. Who wants to stop hearing about Romanian coal mining?

Now, for the closure of the remaining mining operations in Valea Jiului, there are projects, U.E. funds. and budgetary, but the technical projects must take into account the aspects presented in 2006 by the Ministry of Environment, Waters and Forests. In the future of the Valea Jiului there is a danger of a gradual or sudden sinking, and the occurrence of a medium intensity earthquake can lead to a major disaster in this micro-region, including communities and the environment [14].

The Research Center for Sustainable Urban Regeneration-Valea Jiului (CCRUD-VJ) [14] considers that for the Valea Jiului, in the conditions of closing all mines until 2024, a General Project for Sustainable Urban Regeneration of Valea Jiului Microregion is needed, carried out by University of Petroșani.

CCRUD-VJ wants to create together with the City Halls of the Valea Jiului localities, a digital Platform, which through local partnership, to inventory and research the potential of local resources (human capital, natural capital, material capital, investment capital a.o.) and solve the problem lands and buildings of brownfields type (disused industrial areas) from Valea Jiului mining perimeters, by creating a Monitoring and Control Office for Valea Jiului Mining Perimeters, within which will be pursued: • Natural risk maps for landslides or diving, in the mining perimeters of the Valea Jiului; • Monitoring the deformation of surface lands and constructions; • Identification of high risk areas and buildings; • Realization of the deformation forecast of lands and constructions; • Restoration of land that has reached stabilization; • Monitoring the stability of dumps, tailings ponds, roads, buildings, ash depots, etc.

• Monthly newsletter for City Halls, on the situation of mining perimeters and the measures required; • By verifying the Cessation Project of the mine and the Technical Execution Project for the closure of the mine, CCRUD-VJ., Can bring additional additions and measures, which aim at: avoiding the phenomena of sudden sinking; mine enclosures and roads; dumps; ownership regime.

These Responsible for the supervision of the mining perimeters will be able to carry out a prevention activity within the City Halls and together with the Bureau of Monitoring and Control of the Mining Perimeters from Valea Jiului within CCRUD-VJ will ensure that the realization and direction of the technical projects in accordance with and in safety. From the researches of the specialists from the University of Petroşani it is clear that in the mining perimeters there are and will be sinking of the surfaces, and these areas will have to be delimited, fenced and monitored. Within the activity of these Offices, it will be possible to identify all the citizens' alerts, solutions will be proposed for the affected areas, and the monthly reports will be presented D.G.R.M. We consider necessary the preventive actions because the sudden closure of the mines in the Valea Jiului took the Local Public Administrations, the Ministry of Economy, the Ministry of Energy, the Ministry of Regional Development and Public Administration, the Ministry of European Funds, the Ministry of Environment, the Ministry of Waters and Forests, the Ministry of Public Finance, The Ministry of Labor and Social Justice and the National Agency for Mineral Resources. Even if we are now talking about a restriction of the public administration staff, the 69

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Valea Jiului micro-region is a very special area, where it is necessary to supervise the execution of the technical projects for closing the mines. According to the Mining Framework Regulations, the provision of a designated person to keep in touch with the community and the "open doors" program do not ensure peace in the Valea Jiului community. For the Technical Project for the closure of the mine, the designer is obliged to obtain several agreements and approvals, including the Construction Permit, issued by the County Council. It is not necessary to consult or approve the City Hall in the area where the mine is located, which is a serious issue. After the completion of the works, the land areas are handed over by DGRM, to the Local Public Authorities. The fact that, only at the end, the City Halls enter a role, is negatively signaled by the Ministry of Environment, Waters and Forests, since 2006.

A negative and dangerous impact on the environment is represented by quarries and tailings dumps. They were not included in programs and projects for the consolidation of adjacent areas and fencing, and nature entered its role, with landslides and landslides, and people, digging for scrap metal.

Also, the tailings ponds at the Coroieşti Preparation Plant are a "powder keg" for the environment. There is no plan or project to consolidate and secure the dams of these ponds. A natural disaster of red code or an earthquake of medium intensity, can produce an ecological disaster on the Jiu River and even on the Danube.

The Ministry of Environment, Waters and Forests at that time, states in the Mine Closure Report, that in the next period many mining perimeters will be closed, and taking into account the requirements of the European Union Directive no. 2006/21/EEC on the management of extractive waste (the obligation to inventory closed mining areas and their classification according to the danger they pose), in order to improve the process of closing mines and quarries, are necessary [13].

• The global and non-sectoral approach to the environmental issues in the mining perimeters subject to closure and the inclusion in the technical projects for the closure of the activity, of all aspects that have created environmental damage. For example: mine drainage, underground surface water infiltration, funnels and subsurface gaps, mine tailings dumps, surface and underground mining constructions, mining enclosures, access roads etc.

• Establishing in the Cessation Plans (PIA) and in the Technical Projects for Closure of Mines and Environmental Recovery (PT) the possibilities of recovery and use of methane from closed mines, use of mine water as a raw material for hydrogen production (for example), the reprocessing of landfills for the purpose of recovering the carbon fraction and, possibly, for the use of materials recovered in construction, solutions for post-closure redevelopment of closed mines and related dumps, by creating a natural, anthropic and cultural necessary for the development of an ecological tourism in that area etc.

• Establishing from the phase of Cessation Plan (PIA) of the land ownership regime. Solving the handing over of the lands occupied by the mining premises, mining constructions, dumps, collapsing funnels, access roads, etc.

• Creating a unitary legislative framework for the process of closing the mining perimeters. Completing and modernizing the specific legislation, respectively issuing new legislative acts and / or regulations according to the new requirements of the European Union Directive on waste management in the extractive industry. Modification and completion of the Mining Law, the Mine Closing Manual, new closing manuals for salt and uranium, etc.

The seriousness of the issues reported by the Ministry of Environment, Waters and Forests in the 2006 Mine Closure Report did not sensitize the ministries involved to control and manage a situation that may have special consequences in the medium and long term, and proposals to improve the closure process remained the same stage, only as proposals [14].

5. Conclusions Although Valea Jiului is a mining basin of Romania where a coal mine is exploited, which has important balance reserves, currently there are only two viable mines (Livezeni and Vulcan), which can no longer ensure the requirements of the beneficiaries.

Thus, from a first-class mining basin, we are witnessing today, after three decades, the lack of a future energy strategy, to which are added more general causes such as the strategy to reduce carbon dioxide emissions, efficiency lower coal-based energy economy, the development of unconventional less polluting energy sources at a sad end of mining in the Valea Jiului.

The closure of the mines started in 1990 (Iscroni mine) and continues today based on the Closure Plans (PIA) and Technical Projects (PT).

The paper, analyzing how these documents are developed, but also how they were made in the field, concluded that a complete analysis, at this date, of the state of the mining perimeters in Valea Jiului that have closed or are in the process Preservation-closure is difficult to achieve for several reasons presented in the paper. However, an analysis of the underground structure of the mines in the Valea Jiului may anticipate the occurrence of post-closure phenomena caused by a number of factors with synergistic action.

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Although in the period 1996-2020 very few controls were carried out by the bodies authorized to verify the manner of execution of the conservation-closure and greening works of the lands released from constructions, the control of the Ministry of Environment, Waters and Forests from 2006 is noticeable. , to verify the manner in which the Câmpu lui Neag and Petrila Sud Mines were closed, as a result of which many problems were reported in the Mine Closure Report and presented in detail in this article.

The seriousness of the issues raised in this Report did not sensitize the ministries involved to control and manage a situation that may have significant consequences in the medium and long term, and proposals to improve the closure process remained at the same stage, only as proposals.

Finally, it is considered that the proposal made by the Research Center for Sustainable Urban Regeneration-Valea Jiului (C.C.R.U.D.-V.J.) are relevant, achievable and strictly necessary for the sustainable urban regeneration of the Valea Jiului micro-region.

References [1] Cozma E., 2006 Techniques and technologies for closing mining operations (in Romanian), Focus Publishing [2] Davidoiu A., 2017 The role of coal exploitation in Valea Jiului on the sustainable future of the region -(in Romanian), Doctoral thesis, Petroșani University [3] Fodor D., Georgescu M., 2017 Mining rescue solutions from Valea Jiului, (in Romanian and English), Mining Revue, vol.22, no. 4/2017 [4] Furtună P., 2002 Solutions regarding the closure and conservation of some mines in Valea Jiului basin (in Romanian), - Doctoral thesis, University of Petroșani [5] Georgescu M., 2020 Mining in the 21st century, (in Romanian and English), Mining Revue no. 4/2020 [6] Marian D.P., Onica, I. et al., 2019 Study on establishing the causes of the phenomenon of discontinuous subsidence in the Lupeni mining perimeter, (in Romanian), Contract no. 1696 APS / 05.12.2018, University of Petroșani [7] Muzuran C., 2017 Recovery of the technical-productive infrastructure of the mines in liquidation, (in Romanian), Universitas Publishing House, Petroșani [8] Roman Liliana, 2021 Critical analysis of mine closure methods in Valea Jiului (in Romanian), -Scientific research report no.2. University of Petroșani [9] Roman Liliana, 2021 Analysis of subsidence phenomena occurring in the closed mining perimeters of Valea Jiului (in Romanian), - Scientific research report no.3. University of Petroșani [10] *** Mining Law no. 85/2003 (in Romanian) [11] *** Mine Closure Manual - Order 273/2001 (in Romanian) [12] * * * Termination Plans (PIA) and Technical Projects (PT) for mines Uricani, Paroșeni, Aninoasa, Petrila, Lonea, SC I.C.P.M SA, Petroșani 2001-2011 (in Romanian) [13] * * * Post-closure monitoring of underground and surface insulation mining constructions, SC I.C.P.M SA, Petroșani 20012011 (in Romanian) [14] * * *, 2019 Closure plan for access to State aid to facilitate the closure of uncompetitive coal mines Prepared in accordance with Council Decision 2010/787 / EU on State aid to facilitate the closure of non-competitive coal mines. (in Romanian).

This article is an open access article distributed under the Creative Commons BY SA 4.0 license. Authors retain all copyrights and agree to the terms of the above-mentioned CC BY SA 4.0 license.

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EFFECT OF BENEFICIATION ON THE CHARACTERIZATION OF GETSO KAOLIN Nurudeen SALAHUDEEN 1*, Ahmad A. MUKHTAR2 1

Department of Chemical and Petroleum Engineering, Bayero University, Kano, Nigeria, nsalahudeen.cpe@buk.edu.ng 2 Department of Chemical and Petroleum Engineering, Bayero University, Kano, Nigeria

DOI: 10.2478/minrv-2021-0036 Keywords: Getso kaolin; Clay; XRD; pH; Specific gravity Abstract: In their raw forms, clay minerals are found with a number of inherent impurities which make them unsuitable for most industrial applications. In order to overcome this problem and add value to clay minerals, beneficiation process is an indispensable solution. This study investigates effect of wet beneficiation process on the characteristics of a local clay mined from Getso village of Kano State, Nigeria. Mineralogical characterization of the clay was carried out using X-ray diffraction (XRD) analyzer. Chemical characterization of the clay was carried out using X-ray fluorescence analyzer. Physicochemical characterization of the clay was carried out using pH meter and density analysis conducted using density bottle. XRD analysis of Getso clay showed that the raw clay had 8 wt% kaolinite and 51% quartz. Wet beneficiation resulted into 53% improvement of the kaolinite content and 47% reduction of quartz impurity.

The XRF analysis has shown that silica-alumina ratio of the raw Getso clay was 1.55 and this reduced to 1.49 after beneficiation. The physicochemical characterization of the clay has shown that Getso clay is neutral, the raw clay and beneficiated clay had average pH values of 7.5 and 7.3, respectively. Specific gravity values of the raw and beneficiated clay were 2.24 and 2.04, respectively. The beneficiation process had been effective as substantial increase in kaolinte content was observed and a reasonable decrese in the impurity contents was observed from the raw to the beneficiated clay. The Garnet content was completely reduced to zero while quartz, clinochlore and orthoclase were reduced by 24%, 9% and 13% respectively. The clay obtained after the beneficiation be serve as good raw material for production of whitewares, high grade ceramics in synthesis of zeolitic materials.

1. Introduction Clay is a layered structures of fined-grained minerals which occur naturally [1]. Clay material has particle size of about 1 μm [2]. Clay is a fine textured material produced by the weathering process of granite and feldspathic rocks [3,4]. The small particle size and huge surface to volume ratio properties of clay impact on them excellent properties such as high cation exchange capacities, catalytic properties, and plastic behavior needed for their industrial applications [5]. Clay is formed in various classifications each having a distinctive mineral and crystal structural pattern. Each classification of clay possesses a set of unique structural and physical properties which differentiate it from other members of the clay family. They various classifications include; kaolinite, montmorillonite, illite, vermiculite and chlorite. Clay is known for its long use by human for production of ceramic materials as far back as the early stage of human civilization [6]. Modern applications of clay include ceramics application in producing products such as whitewares, high temperature porcelains, sanitary ware and electrical insulators [7].

Kaolinite has been the major class of clay used in the production of ceramic and whiteware porcelain.

Kaolin also called china clay is a high demanded raw material used in production of variety of industrial products which include housewares, building materials ceramics, porcelain, paint, paper, white incandescent light bulbs, skincare products etc [8]. In addition, kaolin I also applied in pharmaceutical, and composite

*

Corresponding author: Nurudeen Salahudeen, Assoc. Prof., Bayero University, Kano, Nigeria, (PMB 3011, Gwarzo Road Kano, Nigeria, nsalahudeen.cpe@buk.edu.ng) 72

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materials industries [9]. Kaolinite group is chemically represented as Al2Si2O5(OH)4. Structurally it possesses one silica and one alumina unit molecules stacked in alternating fashion known as 1:1 lattice type [10]. The choice of kaolin for industrial applications is largely dependent on its purity [11]. Nigeria has been reported to have huge reserves of kaolin mineral which can be harnessed for great economic benefits [12].

This work is aimed at investigating effect of beneficiation on the characteristics of Getso kaolin with the objective of improving the suitability of the clay for industrial applications.

2. Materials and methods 2.1. Materials and Equipment The raw clay was mined from Getso village in Gwarzo Local Government Area, Kano State, Nigeria. The deposit’s GPS coordinate was 11º 53ʼN north and longitude E 7º 58ʼE. Equipment used include, pH Meter (Model; 3510 pH meter), XRD machine (Model; BRUKER S2 RANGER). Apparatus used include weighting balance, glassware and density bottle.

2.2. Methods 2.2.1. Beneficiation Wet beneficiation of Getso clay was carried out as presented in our previous work [13]. The raw clay was crushed and ground. The ground clay was soaked overnight in water in a predetermined ratio of 0.1 g/L. The clay-water mixture was plunged by stirred for 3 h then left to settle. After letting, the supernatant water was decanted and the sedimented clay was sieved using mesh size of #200. The fine clay filtrate known as the beneficiated clay was dewatered, dried, ground and weighted. The residue impurity was collected, dried and weighted.

2.2.2. XRD analysis The clay sample was pulverized, homogenized and a wafer of the clay was made. The clay wafer was mounted on the sample stage in the XRD cabinet. The sample was analyzed using the reflection-transmission spinner stage at Theta-Theta settings. XRD scan was carried out at 2θ range of 4⁰ – 75⁰ using 2θ step of 0.026261⁰ at 8.67 s/step. Tube current was set at 40 mA and the tension was 45 VA. 2.2.3. X-ray fluorescence analysis The clay sample was pulverized, homogenized and a wafer of the clay was made. The clay wafer was mounted on the sample stage in the XRF cabinet for the determination of the metallic oxides compositions.

2.2.4. Physicochemical analysis Specific gravity analysis was carried out using density bottle. Using a weighting balance, weight of empty density bottle was measured as W1. Weight of the bottle plus clay filled to the bottle mark was measured as W2. Weight of the bottle plus clay plus water was measured as W3. Weight of the bottle plus only water filled to the bottle mark was measured as W4. The specific gravity of the clay sample was determined using Equation (1) [14].

Specific gravity = (𝑊

4

(𝑊2 − 𝑊1 ) − 𝑊1 ) − (𝑊3 − 𝑊2 )

(1)

pH analysis was carried out by preparing different samples of clay-water mixtures using 10 g constant weight of clay and varying weight of water so as to make 1:1, 1:2,1:3 and 1:4; wt%-wt% of clay-to-water in each case, respectively. At each experimental run three readings of pH value of the mixture were taken and the average reading was considered for the pH analysis result.

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3. Results and discussion 3.1. Beneficiation Starting with 1500 g raw clay sample for the beneficiation, 1027 g was recovered as the beneficiated clay, implying 68.46% recovery for the beneficiation process. The amount of residue obtained was 327g, implying 21.8% removal of impurity. The remaining 9.7% was loss likely due to soluble impurities, suspended impurities such as organic matters and debris in the raw clay. The residue was the dense mineral impurity which was likely to be quartz.

3.2. XRD Analysis Figure 1 shows the qualitative XRD patterns of the raw Getso clay. It could be observed that the mineral phases present in the raw clay are kaolinite, quartz, orthoclase, clinochlore and garnet. Kaolinite peak which could be observed as the dominant mineral phase was identified at 2θ values of 12.4⁰, 20.5⁰, 24.9⁰ and 35.1⁰ each corresponding to intensity readings of 1500, 500, 1800 and 400 counts, respectively. The quartz phase present were identified at 2θ values of 26.6⁰ and 38.5⁰ which correspond to intensity readings of 9200 and 250 counts, respectively. Other impurities identified include clinochlore at 2θ values of 13⁰ and 25⁰; orthoclase at 2θ values of 36⁰ and 52⁰ and garnet at 2θ values of 39⁰ and 56⁰.

Figure 2 shows the quantitative XRD analysis of raw Getso clay. It could be observed that the kaolinite content of the clay was 8% and the quartz composition was 51%. The of other impurities present were 18%, 16% and 7% for the orthoclase, clinochlore and garnet, respectively.

Figure 1. Qualitative XRD diffractogram of raw Getso clay

Figure 2. Quantitative XRD of raw Getso clay

Figure 3 shows the qualitative XRD patterns of the beneficiated Getso clay. The peaks of kaolinite at 2θvalues of 12.4⁰, 20.5⁰, 24.9⁰ and 35.1⁰ became more prominent in the beneficiated clay. The corresponding intensity readings were 6200, 700, 4800 and 800 counts, for the 2θ values of 12.4⁰, 20.5⁰, 24.9⁰ and 35.1⁰, respectively. The intensity of quartz at 2θ values of 26.6⁰ had reduced drastically from the initial value of 9200 counts in the raw clay to 1500 counts in the beneficiated clay. The peaks for the other impurities could be observed to have reduced similarly.

Figure 4 shows the quantitative XRD analysis of the beneficiated Getso clay. It could be observed that the kaolinite content of the beneficiated clay had improved immensely from the initial value of 8% in the raw clay to 61% in the beneficiated clay. The quartz composition had reduced immensely from the initial value of 51% in the raw clay to 27% in the beneficiated clay. Garnet was completely absent in the beneficiated clay while orthoclase and clinochlor had each reduced by 5% and 7% respectively.

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Figure 3. Qualitative XRD diffractogram of Beneficiated Getso clay

Figure 4. Quantitative XRD of Beneficiated Getso clay

Table 1 presents a tabular analysis of the XRD results of Getso clay before and after beneficiation. It could be observed that the major kaolinite peaks at 2θ values of 12.4⁰ and 24.9⁰ had intensities of 1500 and 1800 counts, respectively in the raw clay. These kaolinite intensities increased by 313% and 166%, respectively after the beneficiation process. Quantitatively this translated into 53% increase in the kaolinite content. The beneficiation process had been effective as substantial decrese in the impurity content could be observed from the raw to the beneficiated clay. The Garnet content was completely reduced to zero while quartz, clinochlore and orthoclase were reduced by 24%, 9% and 13% respectively.

Table 1. Analysis of the XRD results for the raw and beneficiated Getso clay

Constituent Mineral kaolinite Quartz Clinochlore Orthoclase Garnet

XRD Major Peak (⁰) 12.4 & 24.9 26.6 13 52 39

Intensity (Count) Raw Clay Beneficiated Clay 1500 & 1800 6200 & 4800 9200 1500 2000 750 650 50 650 200

Quantitative XRD (%) Raw Clay Beneficiated Clay 8 61 51 27 16 7 18 5 7 0

3.3. Chemical Characterization The XRF chemical compositions of the raw and beneficiated Getso clay are as presented in Table 2. The silica-alumina ratio of the raw clay which was 1.55 reduced to 1.49 after the beneficiation process. This was likely due to the removal of silica components such as quartz as already determined in the beneficiation and XRD results. A complete absence of MgO was observed after beneficiation. This was likely due to complete removal of magnesium-containing impurities during the beneficiation process. Other metallic oxides which reduced as a result of the beneficiation were P2O5 and MnO. Table 2. X-ray fluorescence results of Getso clay

Oxide (wt%) Raw Beneficiated

SiO2 55.68 55.51

Al2O3 35.95 37.30

Fe2O3 2.48 3.13

K2O 1.42 1.47

P2O5 0.83 0.59

MgO 0.59 0.0

MnO 0.31 0.20

CaO 0.3 0.43

TiO2 0.23 0.30

3.4. Physicochemical Characterization 3.4.1. pH analysis The pH analysis results of the various clay-water mixture are as presented in Table 3. The raw Getso clay had an average pH value of 7.5. Beneficiation of the clay reduced the pH value marginally as the beneficiated clay had pH value of 7.3. It could be inferred that either in the raw or beneficiated form Getso clay is neutral.

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The neutrality was enhanced by the beneficiation process as the pH value of the clay was closer to 7.0 absolute neutral point after beneficiation.

Table 3. pH analysis of Getso clay

Clay to water ratio pH of raw clay pH of beneficiated clay

1:1 7.7 7.2

1:2 7.5 7.3

1:3 7.4 7.3

1:4 7.4 7.4

Average pH of Sample 7.5 7.3

3.4.2 Specific gravity Table 4 presents the specific gravity analysis of Alkalari clay. Applying Equation (1) the specific gravity of the raw clay was determined as 2.24. After beneficiation the specific gravity of the clay reduced by 9%.

This was likely due to the effect of quartz removal as quartz is the densest constituent of a clay [13]. This result further validates results of the beneficiation and XRD which earlier suggested removal of quartz during beneficiation.

Table 4. Specific gravity analysis of Alkalari clay

Weight (g) W1 W2 W3 W4 Specific gravity

Raw Clay 29.3 72.4 102.2 78.3 2.24

Beneficiated Clay 29.3 80.3 104.4 78.3 2.04

4. Conclusion Mineralogical characterization of raw Getso clay has revealed that the clay was a kaolin clay having high content of mineral impurities such as quartz, orthoclase, clinochlore and garnet. The raw clay contained only 8 wt% kaolinite and 51% quartz. However, the beneficiation process was quite effective as it improved the kaolinite content by 660% while the quartz impurity was decreased by 47%. The chemical characterization has shown that silica-alumina ratio of the raw Getso clay was 1.55 and this reduced to 1.49 after beneficiation due to reduction in quartz and other dense impurities. The beneficiation process resulted into complete removal of MgO and reduction of P2O5 and MnO impurities. The physicochemical characterization has shown that Getso clay is neutral having average pH values of 7.5 and 7.3 for the raw and beneficiated clay, respectively.

The specific gravity of the raw Getso clay which was 2.24 reduced by 9% after beneficiation. It could be referred that good commercial grade china clay could be produced from Getso clay if it undergoes wet beneficiation process. The china clay produced could be serve as an excellent raw material for production of whitewares such as tiles, high grade ceramics and even used in synthesis of high-tech materials such as zeolite catalysts [15].

References [1] Zhang Z., Wang H., Yao X., Zhu Y., 2012 Effects of halloysite in kaolin on the formation and properties of geopolymers. Cement and Concrete Composites, Vol. 34, pp. 709–715.

[2] Fabbri B., Gualtieri S., Leonardi C., 2013 Modifications induced by the thermal treatment of kaolin and determination of reactivity of metakaolin. Applied Clay Science, Vol. pp. 73, 2–10.

[3] Hassan, M.D., 2014 Geochemistry and Origin of the Cretaceous Sedimentary Kaolin Deposits, Red Sea. Egypt. Geochemistry, 74, pp. 195203.

[4] Huggett, J.M., 2015 Clay Minerals, Reference Module in Earth Systems and Environmental Sciences, Elsevier. DOI: 10.1016/B978-0-12409548-9.09519-1

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[5] Rashad A.M., 2013 Metakaolin as cementitious material: history, sources, production and composition – A comprehensive overview.

Construction and Building Materials, Vol. 41, pp. 303–318.

[6] Bergaya F., Lagaly G., 2013 Handbook of Clay Science, 2nd Edition, Elsevier Ltd., pp. 118 -1295.

[7] Reed, J.S., 2001 Introduction to the Principles of Ceramic Processing New York: John Wiley, pp. 20-23.

[8] Angela M., Moses E., Dumebi O., Simisola T., Felix I., Francis E., Emeka O., 2020 Parametric investigation of indigenous Nigeria mineral clay (Kaolin and Bentonite) as a filler in the Fluid Catalytic Cracking Unit (FCCU) of a petroleum refinery. Alexandria Engineering Journal, Vol. 59, pp. 5207-5217.

[9] Murray H.H., 2006 Applied Clay Mineralogy: Ocurrences, Processing and Application of Kaolins, Bentonites, Palygorskite-Sepiolite, and Common Clays: Development in Clay Science. 2nd Edition, Elsevier, Amsterdam.

[10] Ya W.D., Fang L.T., Yan W., Xiaodong W., Guannan L., Long Z., 2021 Facile preparation of kaolin supported silver nanparticles mediated by Thymbra spicata extract and investigation of the anti-human lung cancer properties. Journal of Saudi Chemical Society, Vol. 25, pp. 101303.

[11] Ayman A., Faris M., Ruba A., 2020 Synthesis of Kaolin-based alkali-activated cement: carbon footprint, cost and energy assessment. Journal of Materials Research and Technology, Vol. 9, No.4, pp. 8367-8378.

[12] Omowumil O.J., 2000 Characterization of some Nigerian Clay as Refractory Materials for Furnace Lining. Nigerian Journal of Engineering Management, Vol. 2, No. 3, pp. 1-4.

[13] Salahudeen, N., 2018 Metakaolinization effect on thermal and physiochemical properties of kankara kaolin. Int j Appl Sci Technol, Vol. 11, No. 2, pp. 127-135.

[14] Salahudeen N., Mohammed U., Yahya M.N., 2021 Chemical, Morphological Characterizations of RiriwaiBiotite and Determination of Yield Point of its WeightingAgent Application in Drilling Mud. Nigerian Journal of Technology, Vol. 40, No. 20, pp. 269–274.

[15] Salih K.K., Burcu A., 2020 One pot fusion route for the synthesis of zeolite 4A using kaolin. Advanced Powder Technology, Vol. 10, pp. 43364343.

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Revista Minelor – Mining Revue ISSN-L 1220-2053 / ISSN 2247-8590 vol. 27, issue 4 / 2021, pp. 78-82

MINERALOGICAL, PHYSICOCHEMICAL AND MORPHOLOGICAL CHARACTERIZATION OF OKPELLA CLAY Nurudeen SALAHUDEEN 1*, Aminat Oluwafisayo ABODUNRIN 2 1

Department of Chemical and Petroleum Engineering, Bayero University, Kano, Nigeria, nsalahudeen.cpe@buk.edu.ng 2 Department of Chemical and Petroleum Engineering, Bayero University, Kano, Nigeria

DOI: 10.2478/minrv-2021-0037 Keywords: Okpella clay, characterization, XRD, XRF, SEM, pH, Specific gravity Abstract: Local clay mineral was mined from Okpella Town, Etsako Local Government Area of Edo State, Nigeria. Mineralogical characterization of the clay was carried out using X-ray diffraction analyzer. Chemical characterization of the clay was carried out using X-ray fluorescence analyzer and the pH analysis of the clay was carried out using pH meter. The mineralogical analysis revealed that the clay was majorly a dolomite mineral having 72% dolomite. The impurities present are 18% cristobalite, 4.1% garnet, 5% calcite and 1% quicklime. The pH analysis of the clay revealed that the clay was acidic having average pH value of 3.9. The pH determined for the 1:1, 1:2, 1:4, 1:8 and 1:10 samples were 3.61, 3.85, 3.85, 4.05 and 4.09, respectively.

1. Introduction Clay is a naturally occurring powder mineral formed by the weathering action of rocks, majorly granite feldspathic and igneous rocks [1]. Clay minerals are layered type hydrous aluminosilicates. Their chemical structures are made of layers of silica and alumina sheets stacked upon each other in a specific pattern. Particle size of clay mineral is in the range of 1 – 2 μm. Clay minerals are the major constituent of fine-grained sediments and rocks [2,3]. Clay minerals possess different classifications based on the number of alumina and silica sheets involved in their structural architecture. The major structural classifications of clay are the 1:1 and 1he 1:2 structural types. The structural classifications of clay determine their mineral categories which include kaolinite, montmorillonite, illite, vermiculite and chlorite [1]. Each of these classifications of clay possess their unique properties which make them preferable in some specific industrial applications where clay is needed.

However, clay generally possess a set of excellent properties that make them suitable for a wide industrial and domestic applications. These properties include plasticity, chemical and temperature resistance, malleability, and complex composite formulations.

Clay is used in a variety of industrial applications such as including paper processing, cement manufacturing, chemical filtration, water treatment, cement manufacturing, paint processing, agricultural soil treatment, ceramic processing and building and road construction. [4, 5, 6]. Clay and other clay-like materials such as dolomite and limestone powder have been widely used as supplementary cementitious material (SCM) in the modern construction industry [7,8, 9].

Dolomites are subsurface cements and replacements that form below active phreatic zone reflux and mixing zones in permeable intervals flushed by warm to hot magnesium-enriched basinal and hydrothermal waters [10]. Dolomite is a natural mineral found in seabed and rock deposits among others. Dolomite chemical structure contains layers of carbonate separated by alternating layers of calcium and magnesium ions make up the ideal structure of stoichiometric dolomite [11, 12]. The mineral name got its origin as a name in honour of a French geologist Deodat Guy de Dolomieu [13]. Dolomite belongs to the flux and building minerals category and is used in the iron and steel and Ferro-alloys industries [14]. Dolomite is chemically represented as CaCO3.MgCO3 and it theoretically contains 54.35% of CaCO3 and 45.65% of MgCO3 [13, 14, 15]. Although, in nature dolomite does not occur in this precise proportion due to presence of impurities. Therefore, the rock having 40–45% MgCO3 is commonly referred to as dolomite.

*

Corresponding author: Nurudeen Salahudeen, Assoc. Prof., Bayero University, Kano, Nigeria, (PMB 3011, Gwarzo Road Kano, Nigeria, nsalahudeen.cpe@buk.edu.ng) 78

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This study is aimed at determining the mineralogical and chemical characteristics of Okpella clay so as to provide an informed insight on its economic viability in terms of determining its suitable industrial application.

2. Materials and methods 2.1. Materials Okpella clay was collected from Okpella deposit, Etsako Local Government Area of Edo State, Nigeria.

Equipment used include X-ray Diffraction machine (Model; Rigaku MiniFlex), scanning electron microscopy (Model; Phenom ProX), weighing balance and X-ray fluorescence machine (Model; SKYRAY-EDX3600B).

Other apparatus and materials used include pH meter and glassware.

2.2. Methods Sample to be analyzed was pulverized to powder size and pressed to make thin layer which was placed in a flat sample holder of the XRD machine. XRD scan was carried out at Bragg’s angle range of 5⁰ - 70⁰ with a Bragg’s angle interval of 0.026261 at 8.67 seconds per step. The X-ray tube was operated at 40 mA and 45 VA. X-ray fluorescence analysis was conducted using SKYRAY-EDX3600B. Scanning electron microscopy (SEM) was carried out using Phenom ProX Desktop SEM. Sample wafer was placed in the sample chamber of the SEM machine and the SEM gun was focused on a selected area of the sample at certain magnification.

The electron gun shot a beam of high energy electrons on the focused area to generate a SEM micrograph of the sample. pH analysis was conducted by inserting the electrode of pH meter in clay-water mixture. Various samples of clay-water mixtures using 10 g constant weight of clay in varying weight of water to make 1:1, 1:2,1:4, 1:8 and 1:10; wt%-wt% of clay-to-water were prepared and analyzed.

3. Results and discussion 3.1. X-ray diffraction analysis Figure 1 shows both the qualitative and quantitative XRD analysis of Okpella clay. The qualitative analysis present results of the Bragg’s angle in degree against the intensity in count of the various mineral present in the clay. Analysis of the quantitative XRD revealed that Dolomite phase was identified at Bragg’s angle values of 31.06⁰, 41.28⁰ and 51.13⁰. Quartz (Cristobalite) phase was identified at Bragg’s angle values of 21.66⁰ and 69.11⁰. The peaks for Garnet phase were at Bragg’s angle of 22.20⁰ and 60.0⁰. The peaks for Calcite were at Bragg’s angle of 29.63⁰ and 45.04⁰. The peaks for Quicklime were at Bragg’s angle of 33.6⁰ and 37.33⁰. The quantitative XRD analysis shown as the pie chart in Figure 1 revealed quantities of the various minerals present in the clay. It could be observed that Dolomite, Quartz (Cristobalite), Garnet, Calcite and Quicklime were present at 72%, 18%, 4.1%, 5% and 1%, respectively.

Figure 1. X-ray Diffraction of Okpella clay 79

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3.2. X-ray fluorescence analysis Table 1 presents the XRF chemical composition analysis of Okpella clay. The SiO2 content of the clay was 37.4 wt% and the AL2O3 content was 7.6 wt%. The silica-alumina content of the clay was high having value of 4.9. of 41.61%. Although the silica and alumina content of the clay were higher than values reported for pure dolomite [14], the silica-alumina ratio falls within reported values [14]. CaO was the highest metallic oxide having value of 42.6 wt%, this is consistent with report by other researchers [13,14]. The high CaO content further validates the XRD result showed that dolomite was the highest single-phase mineral present in Okpella clay. The other substantial metallic oxides compositions of the clay were MgO and Na2O which were present at 7.5 and 3.8 wt%, respectively. The MgO which is also a key chemical constituent of dolomite was lower in the current study than 12.8 wt% reported by Pradeep et al., [14] for a pure dolomite. The substantial presence of Al2O3 was as a result of alumina presence in garnet while high SiO2 was due to its presence in the cristobalite impurity. Other metallic oxides such as K2O, Fe2O3, TiO2, P2O5 and SrO were only present in trace quantities less than 0.3 wt%. Their presence could be attributed to the presence of associated impurities in the clay.

Table 1 X-ray fluorescence analysis of Okpalla clay

Metalic Oxide CaO SiO2 Al2O3 MgO Na2O SO3 K2O Fe2O3 TiO2 La2O3 P2O5 SrO

wt% 42.6 37.2 7.6 7.5 3.8 0.3 0.2 0.2 0.1 0.1 0.1 0.1

3.3. pH analysis Table 2 presents the pH analysis of Okpella clay. It could be observed that at the various water to clay ratio the pH was at acidic range having the lowest value of 3.61 at the 1:1 ratio sample. The pH value increased marginally with increase in the water content of the clay-water mixture. The highest value was recorded at 1:10 sample having pH value of 4.09. Using Equation (1) the average pH of the clay was determined as 3.9.

The acidic pH of the clay suggested that the clay originated from weathering of igneous rock [16]. Also, the acidic pH was possibly due to presence of some acidic impurities which may be sulphate salt as the presence of 0.3 wt% of SO3 was confirmed in the XRF result of the clay.

Table 2. pH analysis of Okpella clay at varying ratio of clay-water mix

1:1 3.61

Clay-water ratio pH Average pH =

∑ 𝑝𝐻 𝑛

=

19.45 5

1:2 3.85

1:4 3.85

= 3.9

1:8 4.05

1:10 4.09 (1)

3.4. Scanning electron microscopy Figures 2(A), 2(B), 2(C) and 2(D) show the SEM micrographs of Okpella clay at 300x, 500x, 1000x and 1500x magnifications, respectively. Analysis of the micrograph shows that the clay possessed dispersed morphology having tetrahedral crystal shape with some level of crystal defects. The average particle size was estimated to be 350 𝜇m.

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Figure 2. SEM image of Okpella clay at; (A) 300x magnification; (B) 500x magnification (C) 1000x magnification; (D) 1500x magnification

4. Conclusion Mineralogical characterization of Okpella clay has shown that the clay is a dolomite mineral consisting of 72% dolomite. Other impurity phases present in the clay were cristobalite, garnet, calcite and quicklime, they were present by 18%, 4.1%, 5% and 1%, respectively. Chemical characterization of the clay further confirmed presence of dolomite as indicated by substantial content of CaO and MgO at 42.6 and 7.5 wt%, respectively. The XRF analysis further confirmed presence of cristobalite and quicklime as impurity phases present in the clay as indicated by the substantial SiO2 and Na2O content of 37.2 and 3.8 wt%, respectively.

Although, Okpella clay was majorly a dolomite mineral it also contained some impurity minerals which were responsible for the its higher Al2O3 and SiO2 content compared to reported values [14] for a pure dolomite.

SEM Analysis of Okpella clay has shown that the clay possessed dispersed morphology having defective tetrahedral crystal shape. The pH determined for the 1:1, 1:2, 1:4, 1:8 and 1:10 clay-water mixture samples were 3.61, 3.85, 3.85, 4.05 and 4.09, respectively. The average pH of the clay was 3.9. The acidic pH of the clay suggested that the clay originated from weathering of igneous rock [16]. The acidic pH of the clay could also be due to presence of acidic salt impurity which was likely a sulphate salt as suggested by the XRF result which shows presence of 0.36 wt% SO3. In view of the findings of this study Okpella dolomite is recommended as a good raw material for production of cement. The dolomite content can even be improved if beneficiation of the clay is carried out.

References [1] Raj M., Binoy S., Kumuduni N.P., Jaffer Y.D., Nanthi S.B., Sanjai, J.P., Christian S., Yong S.O., 2021 Natural and engineered clays and clay minerals for the removal of poly- and perfluoroalkyl substances from water: Stateof-the-art and future perspectives. Advances in Colloid and Interface Science, Vol. 297, No.1, pp. 102537.

[2] Zunino F., Scrivener K., 2020 Increasing the kaolinite content of raw clays using particle classification techniques for use as supplementary cementitious materials. Construct and Building Materials, Vol. 244, No. 1, pp. 118335.

[3] Huggett J.M., 2015 Clay Minerals, Reference Module in Earth Systems and Environmental Sciences. Elsevier, Amsterdam.

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[4] Liu P., Farzana R., Rajarao R., Sahajwalla V., 2017 Lightweight Expanded Aggregates from the Mixture of Waste Automotive Plastics and Clay. Construction and Building Materials, Vol. 145, pp. 283-291.

[5] Salahudeen N., 2018 Metakaolinization effect on thermal and physiochemical properties of kankara kaolin. International Journal of Applied Science and Technology, Vol. 11, No. 2, pp. 127-135.

[6] Hassan M.D., 2014 Geochemistry and Origin of the Cretaceous Sedimentary Kaolin Deposits, Red Sea, Egypt. Geochemistry, Vol. 74, pp.

195-203.

[7] Khan M.S.H., Nguyen Q.D., Castel A., 2020 Performance of limestone calcined clay blended cement-based concrete against carbonation. Advance Cement Research, Vol. 32 No. 11, pp. 481–491.

[8] Krishnan S., Emmanuel A.C., Shah V., Parashar A., Mishra G., Maity S., Bishnoi S., 2019 Industrial production of limestone calcined clay cement: experience and insights. Green Mater. Vol. 7, pp. 15–27.

[9] Kazeem D M., John T.K., Adewumi J.B., Oladimeji B.O., 2021 Comparative performance of limestone calcined clay and limestone calcined laterite blended cement concrete. Cleaner Engineering and Technology, Vol. 4, pp, 100264.

[10] Qiao Z.F., Zhang S.N., Shen A.J., Shao G.M., She M., Cao P., Sun X.W., Zhang J., Guo R.X., Tan X.C., 2021 Features and Origins of Massive Dolomite of Lower Ordovician Penglaiba Formationin the Northwest Tarim Basin Evidence from Petrography and Geochemistry, Petroleum Science, In press, https://doi.org/10.1016/j.petsci.2021.03.001 [11] Kumar B.P., Babu K.R., Rajasekhar M., Ramachandra M., 2020 Identification of land degradation hotspots in semiarid region of Anantapur district, Southern India, using geospatial modeling approaches, Modeling Earth Systems and Environment, Vol. 6 No. 3, pp. 1841–1852.

[12] Madhu T., Kumari O.V., Kumar G.R., Reddy E.C., 2019 Analysis of Geological Factors for Successful Dolomite Mining Exploration at Venkatampalli Village, Narpala Mandal, Anantapur District, Andhra Pradesh. Bulletin of Pure & Applied Sciences-Geology, Vol. 38 No. 2, pp. 218–224.

[13] Warren J., 2000 Dolomite: occurrence, evolution and economically important associations, Earth-Science Reviews, Vol. 52, pp. 1–81.

[14] Pradeep K.B., Raghu B.K., Sree P.P., Rajasekhar M., 2020 Occurrence and structures of dolomites in North Eastern part of Anantapur district, and their use in engineering materials.

Materials Today: Proceedings, In press. https://doi.org/10.1016/j.matpr.2021.07.335.

[15] Wang Z., Torres M., Paudel P., Hu L., Yang G., Chu X., 2020 Assessing the Karst Groundwater Quality and Hydrogeochemical Characteristics of a Prominent Dolomite Aquifer in Guizhou. China. Water, Vol. 12, No. 9, pp. 2584.

[16] Keller W.D., Matlack K., 1990 The pH of clay suspensions in the field and laboratory, and methods of measurement of their pH. Applied Clay Science, Vol. 5, pp. 123-133.

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