Geotechniek september 2005 Special ECSMGE Japan

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GEOTECHNIEK 16th European Conference on Soils Mechanics and Geotechnical Engineering

September 12-16, 2005 Osaka - Japan

Redevelopment of Tilburg Pieter Vreede Square (The Netherlands) calls for innovative building techniques Long-term behaviour of a bored tunnel partly lying in soft soils Designing reinforced embankments on piles: publications in Osaka Influences of Physical Grout Flow around Bored Tunnels

GeoDelft: balance between theory and experiment geo ENGELSTALIG_2005#4v1.indd 1

SPECIAL EDITION 8/10/05 2:45:10 PM


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Preface

Colophon

In 1991, under the supervision of the Dutch Ministry for Economic Affairs, a group of Dutch

Geotechniek Special: 16th European Conference on Soils Mechanics and Geotechnical Engineering

experts visited Japan in order to study the technological developments there with regard to

September 12-16, 2005 Osaka - Japan

establishment of the Centre of Underground Construction (COB) in The Netherlands in 1994

being applied in Japan would also be suitable for soil conditions in The Netherlands. The was a result of this mission.

Publication Uitgeverij Educom BV Mathenesserlaan 347-b, 3023 GB Rotterdam Tel. +32-(0) 10 425 65 44 Fax +32-(0) 10 425 72 25 E-mail: info@uitgeverijeducom.nl Internet: info@uitgeverijeducom.nl

In 1994 the Centre started an extensive research program that, amongst others, comprised

of a practical study of two pilot projects. The second Heinenoord Tunnel for road traffic was

the first pilot project. The pilot projects were designated as such by the government and the aim of these projects was to gather know-how with regard to the boring of tunnels in

typical Dutch subsoil conditions. A lot was learned from the construction of the second Heinenoord Tunnel, and as a result a number of bored tunnels was realised in The Netherlands in recent years:

Publisher Robert Diederiks

• The Botlek Tunnel, the Sophia Tunnel and the Pannerdens Channel Tunnel in the

Betuweroute, an important new railway connection for the transportation of goods

Editorial Board Alboom, ir. G. van Barends, prof. dr. ir. F.B.J. Berg, dr. ir. P. van den Brinkgreve, dr. ir. R.B.J. Calster, ir. P. van Deen, dr. J.K. van Diederiks, R.P.H. Diepstraten, ir. E.M.J. Doornbos, ing. S. Eijgenraam, ir. A.A. Graaf, ing. H.C. van de Graaf, ir. H.J. van der Habib, ir. A. Hannink, ir. G. Huiden, ir. E.J. Jonker, ing. A. Kant, ing. M. de

underground construction. The most important conclusion was that the boring technology

Knol, ir. J. Kooistra, ir. A. Mathijssen, ir. F.A.J.M. Meel, ir. R. van der Ramler, ir. J.P.G. Rook, J. Rijkers, drs. R.H.B. Schouten, ir. C.P. Schrier, ir. J.S. van der Seters, ir. A.J. van Smienk, ing. E. Staveren, ir. M.Th. van Teunissen, ir. E.A.H. Thooft, dr. ir. K. Visser, ing. G.T. Vos, ir. M. de Ypma, ir. M.J.

Editing Berg, dr. ir. P. van den Diederiks, R.P.H. Hannink, ir. G. Kant, ing. M. de Mathijssen, ir. F.A.J.M. Thooft, dr. ir. K. Styling DLMA in association with Uitgeverij Educom BV © Copyrights Uitgeverij Educom BV - September 2005

between the Port of Rotterdam and the Ruhr Area in Germany and beyond;

• The Green Heart Tunnel as part of the High Speed Railway Line from Amsterdam to Paris; • The Westerschelde Tunnel, a tunnel for road traffic with a maximum depth of 65 m underneath the tidal river Westerschelde.

Today The Netherlands is on the eve of the next step: the boring of tunnels in urban areas: • The construction of two bored single-track tunnel tubes in the urban area of Rotterdam for the realisation of a light-rail connection for RandstadRail will start this year;

• The construction of a bored tunnel underneath the old inner city of Amsterdam for the North-South subway line will follow shortly;

• The construction of two bored tubes for the Hubertustunnel in The Hague for road traffic is expected to start at the end of 2006.

Since 1997 the periodical Geotechniek issued by Educom appears quarterly in the Dutch

language. It is only in exceptional cases that Geotechniek appears in the English language. The 16th International Conference on Soil Mechanics and Geotechnical Engineering held in Osaka in 2005 is such an occasion.

This special edition is a tribute to the cooperation with the Japanese geotechnical engineers on tunnelling that exists nowadays. The Dutch geotechnical industry facilitated this edition and presents a number of innovative and interesting on-going projects. Ir. G. Hannink

R.P.H. Diederiks

Chairman of the Editorial

Publisher

Board of Geotechniek © ISSN 1386 - 2758

Geotechniek 16th ICSMGE

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CONTENTS Geotechniek Colophon / Preface

3

Contents

4

Introduction to the special edition

5

Redevelopment of Tilburg Pieter Vreede Square (The Netherlands) calls for innovative building techniques

8

ESCRAVOS GTL – Ground Improvement Scheme Chevron Nigeria

12

Delft Cluster: working on the sustainable development of densely populated delta areas

14

Long-term behaviour of a bored tunnel partly lying in soft soils

16

Designing reinforced embankments on piles: publications in Osaka

20

Influences of Physical Grout Flow around Bored Tunnels

22

GeoDelft: balance between theory and experiment

26

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Introduction to the special edition

Introduction to the special edition Dr. Peter van den Berg Director Research GeoDelft and board member NSSMGE, international affairs

Geotechnics in The Netherlands The Netherlands, especially the densily populated western part of the country, is located several meters below sea-level. Generally speaking, the subsoil consists of 10-20 meters of very soft clay and peat layers. In addition there is a high groundwater level, almost up to the soil surface: a typical delta area. Delta areas all over the world are attractive places to live and to work. On the one hand, they have tremendous economic potential, on the other hand the inhabitants live in the permanent threat of flooding and subsidence of the soft soil. Civil and hydraulic engineering are key factors in managing these challenges and providing sustainable solutions. Apart from the constant threat of water on the one hand and the soft soil on the other, the Netherlands face an additional problem as well. The claims on the available space in the Nether-

\ Figure 1 Failure of peat dike

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lands are becoming bigger and bigger. A solution to cope with this problem has been found into a new, additional direction: the underground. However, building underground in the soft soils of the Dutch delta is not without risks when the available knowledge and experience is limited. Recently, a lot of research has been carried out in the Netherlands in order to create a safe, sustainable and high-quality living “delta” environment for us and our (grand)children. For an overview of the research carried out during the last, say, four years, reference is made to the set of Dutch papers, published in the proceedings of the 16th ICSMGE Conference held in Osaka (2005). Two examples are highlighted here: a recent dike failure and a challenging underground project in the old city centre of Amsterdam.

the boundary between the peat layer and the underlying sand layer. It was concluded that failure was caused by a chain of events in which weight loss and shrinkage of peat, due to the dry weather conditions, are considered to be important factors. Analyses of the behaviour of the peat made clear that several processes, controlled by hydrological conditions in the unsaturated and saturated zones in the embankment, resulted in fracturing of peat. The fracturing along with a very high strength anisotropy of the peat resulted into a connection between the water inside the canal and the water inside the sand layer, raising the piezometric head in the sand by several metres, allowing the dike to simply ‘float’ away for over 5 m, pushed aside by the water inside the canal.

Failure of peat dike A peat dike unexpectedly failed at the end of the dry summer of 2003. The failure mode was not a Bishop type circular failure plane normally used in routine dike stability analyses in the Netherlands. The failed dike segment was displaced horizontally by over 6 m ( figure 1). The failure plane was found to be located at

Metro line in Amsterdam A new North-South metro line is being constructed underneath the old city centre of Amsterdam ( figure 2). The construction of three deep station boxes started in 2003 right in the historic inner city. The sensitive structures surrounding the station boxes are automatically monitored by a system of robotic

\ Figure 2 Metro line in Amsterdam

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Introduction to the special edition

total stations and prisms. A dedicated geographical information system automatically checks on an hourly basis whether individual measuring points have exceeded limit values. The limit values are based on the results of full scale tests and 3D finite element analyses. It appeared to be very important to have such a very sophisticated system to control deformations due to the construction of deep station boxes in this very sensitive historic environment. The large amount of monitoring data, every day several thousands of measuring points are checked for exceeding trigger values, requires special analyses. Once limit values are exceeded clear and comprehensive procedures have been defined to inform geotechnical engineers to take the most accurate action.

Conclusion Many other examples can be worked out to indicate that there are still a lot of challenges for the geotechnical profession. Continuously new impulses are needed to comply with changing conditions: climate change, safety against flooding, settlement and failure of the soft subsoil, new concepts for infrastructure in a densily populated environment, increasing complexity in general in urban environment, asking for new technology and sophisticated risk control systems, and so on. This is a tough challenge for the geotechnical profession. Beside geotechnics, also mechanics, geophysics, geology, biology, chemistry, informatics, planology and law are involved to guarantee a multidisciplinary approach and to seek in close

cooperation the best solution in situations of growing complexity. In our profession there is ample place for advanced technology and innovation such as new monitoring systems, on line data collection and interpretation, probabilistic methods to comply with weighted uncertainties, new materials, modified materials and ground mixing methods, further improvement of prediction models and methods of analysis directed to risk reduction and optimization of design, construction and maintenance. In this manner our profession remains valuable in the eyes of politicians, and policy makers, useful for the entire society and future generations.

Dutch contributions for the 16th International Conference in Osaka The following papers were submitted to the conference by the Netherlands Society for Soil Mechanics and Geotechnical Engineering (NSSMGE): • Anisotropic geomechanical parameters as a result of glacial shearing (authors: L.F. Gareau, F. Molenkamp, J.Sharma, M. Remijn and B. Huang) • Centrifuge modelling of soil up heave by expanding tubes (authors: B.G.H.M. Wichman and H.G.B. Allersma) • Conditions for the use of the observational method in geotechnical engineering (author: S. van Baars) • Dutch research on the impact of shield tunnelling on pile foundations (authors: F.J. Kaalberg, E.A.H. Teunissen, A.F van Tol and J.W. Bosch) • Effect of compaction grouting in loosely packed sand on density (authors: H.M.A. Pachen, P. Meijers, M. Korff and J. Maertens) • Failure of peat dikes in The Netherlands (authors: A. Bezuijen, G.A.M. Kruse and M.A. Van) • Failure probability of dikes strengthened with structural elements (author: H.L. Bakker) • Geotechnical Risk management in the Netherlands (authors: D. Pereboom, P.P.T. Litjens and M.Th. van Staveren) • Influence of loading rate on floating piles in sand (authors: J. Dijkstra, A.F. van Tol, N. Huy and P. Hölscher) • Innovative Restoration of Medieval City Walls Den Bosch by soil nailing (authors: J. Steenbergen-Kajabová, J.W. Bosschaart and H.A.A. Habib)

• Integral design of motorways on soft soil on the basis of whole life costs (authors: A.A.M. Venmans, U. Förster and R.H. Hooimeijer) • Large scale monitoring during Amsterdam metro construction; risk control, procedures and experiences (authors: J.K. Haasnoot, F.J. Kaalberg and S. Braakman) • Liquefaction flow slide at horizontal ground (authors: M.B. de Groot, M. Korff and H.M.A. Pachen) • Monitoring and modelling during tunnel construction (authors: A. Bezuijen, A.M. Talmon and J. Joustra) • Observational Method for Dike Management (authors: R.A.J. v.d. Kamp and E.H. Rob) • Observations on densification of soil during vibratory sheet piling (authors: P. Meijers and A.F. van Tol) • Reduction of the Cone Resistance caused by the installation of CFA piles (authors: G. Hannink and A.F. van Tol) • Reliability of Settlement Prediction based on Monitoring (authors: E.O.F. Calle, H. Sellmeijer and M.A.T. Visschedijk) • Three examples of using artificial neural networks in geotechnical engineering (authors: A.R. Koelewijn and J. Maccabiani) • The synergy between theory and practice in geo-engineering (author: B.R. Hemmen) • Unravelling the Anisotropy of Peat (authors: C. Zwanenburg and F.B.J. Barends) • Validation of design methods with in situ monitoring of deep excavations (authors: M. Korff and J. Herbschleb)

Netherlands Society for Soil Mechanics and Geotechnical Engineering (NSSMGE) The NSSMGE was founded on October 7, 1949 to stimulate knowledge transfer of Geotechnics and related disciplines by: • organising informative meetings, lectures, symposia, excursions, etc.; • installing working groups to study specific geotechnical topics; • supporting scientific research on geotechnics; • exchanging knowledge of geotechnics via the International Society (ISSMGE) and circulating this knowledge to members of the Netherlands Society (NSSMGE); • co-operation with other divisions of the Royal Institute of Engineers (KIVI NIRIA) and organisations related to geotechnics; • organising courses on geotechnics; • supporting the periodical Geotechniek; • proposing members for the Technical Committees of the ISSMGE; • participation in the Centre for Civil Engineering Research and Codes (CUR) and the Dutch Standardisation Institute (NEN).

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For further information contact: Mr. J.H. Beukema, secretary of the NSSMGE, P.O. Box 5044, 2600 GA Delft, The Netherlands, telephone: + 31 15 251 83 53, telefax + 31 15 251 85 55, email: j.h.beukema@dww.rws.minvenw.nl

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Redevelopment of Tilburg Pieter Vreede Square (The Netherlands) calls for innovative building techniques. Abstrac t

A. Verweij Fugro N.V. Fugro Head Office P.O. Box 250 2260 AG Leidschendam The Netherlands Tel. + 31-(0) 70 311 14 22 E-mail: holding@fugro.com Internet: www.fugro.com

\ Figure 1a First excavation stage

\ Figure 1b Second excavation stage

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A large building site is currently being developed in the centre of the Dutch city of Tilburg. The city council of Tilburg planned to redevelop the Pieter Vreede Square in order to revive the city’s centre with a multifunctional area combining housing, shopping, entertainment and underground parking. In order to minimise environmental influence innovative building techniques have been applied in realising the building pit for the underground constructions. Fugro has contributed widely to this project with both geotechnical and geohydrological consultancy and extensive soil investigation during a period of four years.

Introduction The reconstruction of the Pieter Vreede Square covers an area of 14.600 m2. The project combines 124 apartments, shops, restaurants and bars, a cinema and an 800 place underground parking lot. The project location in the historic centre of Tilburg has created many challenges during the design process. Ancient buildings are present at a very close distance to the building site and the presence of industrial pollution at several subsurface levels was known at different locations. The depth of excavation, some 10 m below surface level, a high groundwater level and a stratigraphy of gravely sands and poorly

\ Figure 1c Third excavation stage

interconnected loam layers imposed strict boundary conditions on the building methods to be used.

Preliminary design In order to construct the underground parking lot and shopping area a building pit had to be excavated until approximately 10 m below surface level. At first standard foundation methods using shallow foundations and steel sheetpile walls were investigated. Shallow foundations could be used provided ground improvement was applied on some locations and the loads could be spread efficiently.

\ Figure 1d -3 Floor completed

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Redevelopment of Tilburg Pieter Vreede Square (The Netherlands) calls for innovative building techniques.

restrictions. As a result a building method using a combination of a bored pile wall and a chemical injection layer was considered. As time went by the importance of a watertight building pit became clear, as the city council was strongly opposed to displacement of nearby subsurface pollution. However, using chemical injection the impermeability could not be fully guaranteed. Also, due to legal problems application of grout anchors underneath the surrounding buildings was not possible. Furthermore the location in the city centre imposed logistical problems that ruled out the application of underwater concrete.

\ Figure 2 Excavation of cement-bentonite wall

Calculations showed that unsupported sheetpile walls were not an option, so preliminary design calculations were made using high angle grout anchors. Supported steel sheetpiles could theoretically be applied, however, dynamic analysis showed that vibrating or driving of steel sheetpiles would lead to unacceptable vibrations and high risk of damage to surrounding buildings, so alternative building methods had to be investigated.

Additional analyses In order to build the project as proposed the building pit has to be dewatered. Due to the absence of a shallow laterally continuous impermeable loam layer the draw down values would be too high to meet governmental

\ Figure 3 Installation of concrete sheetpiles

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At this point application of the top-down method came into sight. In combination with the chemical injection layer a nearly watertight pit could be realised. Low draw down rates would lead to little displacement of the surrounding pollution. Although being an expensive solution, the top-down method tackled most of the problems mentioned above. Inconvenience for the public caused by building activities is reduced to a minimum using this method. There is no need for anchorage of the building pit walls as the floors and temporary struts provide lateral support.

Final design Finally the city council of Tilburg demanded zero displacement of surrounding soil and water pollution. This eliminated options for chemical injection and relatively short walls. It was decided to use the clayey Kedichem Formation as sealing bottom of the building pit. The top of this layer is located at approximately 54 m depth. The proposed type

of bored piles cannot be made up to this length, so diaphragm walls of some 55 m length were proposed to provide lateral boundaries for the building pit. The building pit contractor suggested as an alternative the use of a 55 m cement – bentonite wall ensuring lateral impermeability in combination with 18 m prestressed concrete sheetpiles in the top segment of the wall ensuring lateral stability. Application of the top-down method was maintained in the final design. The structural consultant has chosen the following (simplified) staged construction. First the combined cement-bentonite / prestressed concrete sheetpile walls are installed. After installation of the walls the –1 level is to be excavated. Then 670 mm bored steel piles with grout injection are installed with a center-tocenter spacing of 9 m. These piles act as support for the floors during both top-down excavation and service stage. Also vertical grout anchors with a center-to-center spacing of 3 m are installed as tension piles underneath the level of the –3 floor. After this the –1 floor is to be constructed to act as a lateral support for the building pit walls. The –2 and –3 levels are to be excavated subsequently using temporary struts, while at the same time the +0 and +1 floors are being constructed. Using this method only the pit itself has to be dewatered and no displacement of pollution should occur, provided the cement-bentonite walls are watertight. This design is currently under construction.

Fugro’s activities: soil investigation In 2002 Fugro won the bid for preliminary soil investigation and geotechnical engineering

\ Figure 4 Sheetpiles hanging in liquid cement-bentonite suspension

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Squeezing verstoort leidingtracé Redevelopment of Tilburg Pieter Vreede Square (The Netherlands) calls for innovative building techniques.

regarding steel sheetpile walls, a shallow foundation design and geohydrological calculations. As the design process proceeded Fugro carried out a full-scale soil investigation in order to determine the lateral continuity of impervious loam layers and provide sufficient data for a foundation plan. A total of 92 CPT’s have been carried out until now, some with water pressure measurement. Also 10 borings with multiple standpipe piezometers have been drilled and a laboratory plan was carried out.

construction plan. Water levels have been observed in boreholes and standpipes and by literature study. Using MicroFEM Fugro calculated multiple scenarios of partial and total injection of the building pit and for several depths of the surrounding (sheetpile / bored pile / diaphragm) walls. Environmental water quality tests were performed and drainage permit trajectories have been coordinated. Furthermore a work plan has been drawn up for a full scale pumping test in order to establish the building pit’s water tightness. \ Figure 5 Building pit overview after first excavation

Fugro’s activities: geotechnical consultancy Fugro acted as geotechnical consultant to the project construction bureau and carried out foundation design for shallow foundations and pile foundations. Bearing capacity was determined for piles loaded by compression and tension forces and spring characteristics have been assessed for the different pile types and the combined diaphragm walls. Furthermore stability analyses have been made for the several building pit wall types. For the combined cement – bentonite diaphragm wall / prestressed concrete

stage

sheetpile wall a detailed analysis of bearing capacity was carried out using both analytical and FEM calculations. Also the trench stability of an excavated diaphragm wall panel was researched using 3D FEM analysis.

Fugro’s activities: geohydrological consultancy Fugro has investigated every geohydrological aspect concerning this project from the preliminary design stage up to the final

Conclusions Development of large building pits for underground constructions in inner city areas demand a high degree of engineering. Unfortunate subsurface conditions and the presence of nearby pollution at the Pieter Vreede Square site in Tilburg, The Netherlands, accentuated this even more. Fugro has contributed widely to this project with both geotechnical and geohydrological consultancy and extensive soil investigation for the walls, the foundation and dewatering of the building pit.

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ESCRAVOS GTL - Ground Improvement Scheme Chevron Nigeria Dr. Ir. Jean-François Vanden Berghe

Ir. Jean-François Wintgens Fugro Engineers SA/NV

ABSTR ACT

This article summarises an innovative ground improvement scheme (combined surcharge, groundwater lowering and drainage). It is inducing some 6 m settlement of weak soil in the Niger delta. Foundation design in the strengthened soils is also discussed.

Fugro Head Office P.O. Box 250 2260 AG Leidschendam The Netherlands Tel. + 31-(0) 70 311 14 22 E-mail: holding@fugro.com Internet: www.fugro.com

The project Chevron Nigeria Ltd is currently performing major site preparation works for their Gas-ToLiquid (GTL) development at their Escravos oil terminal in Nigeria. The site, which is located in a swamp at the mouth of the Escravos river (Figure 1), is characterized by a series of soft clay layers down to 45 m depth. As described below, ground conditions are poor, and Fugro Engineers S.A. (formerly Thales GeoSolutions) developed an innovative approach for improving them. Ground improvement is being achieved by a combination of sandfill reclamation work, drainage through wick drains and dewatering of the clay layers. At this site ground improvement is the instrument to facilitate economic foundation design. Since an early stage of the project, Fugro Engineers has provided personnel and engineering

consultancy services to Chevron. In 1997, the project was initiated by a conceptual study to define foundation schemes for the GTL plant. To date, Fugro geotechnical engineering consultancy services has included: • analysis of key geotechnical parameters • design of the site preparation and ground improvement concepts • foundation design • supervision of the instrumentation installation and sandfill work • monitoring ground consolidation progress • geotechnical supervision of the works.

Soil conditions Typical soil conditions at the Escravos GTL site comprise four main soil layers. An Upper Clay layer about 16 m thick is underlain by Middle Sand on average 6 m thick. The Middle Sand is underlain by a Lower Clay layer about 22 m

thick. Sand is typically found beneath the Lower Clay starting from about 45 m depth. The existing ground surface is at about Chart Datum level (CD 0 m). Typical ground profile is shown in Figure 2. The available site investigation and test data indicate that both Upper and Lower Clay layers are essentially normally consolidated. The basal sand (CD -45 m) is dense.

Ground improvement The ground improvement scheme comprises sand surcharge, temporary groundwater lowering and drainage. The sand surcharge was installed over the full area of the site to induce consolidation. The surcharge component is a sandfill platform approximately 8 m thick. Platform installation was performed in four phases. During each

PUMP OUT WATER

+6 m CD

5

1

0 m CD

Upper Clay

- 16 m CD

Middle Sand WATER FLOW

- 22 m CD

Lower Clay - 44 m CD

Sand

\ Figure 1 Escravos Gas to Liquid Plant site during sandfill

placement

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PREFABRICATED VERTICAL DRAINS

\ Figure 2 Typical soil profile and ground improvement scheme

Geotechniek 16th ICSMGE

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ESCRAVOS GTL – Ground Improvement Scheme Chevron Nigeria

phase, a sand layer of about 2 m thick was placed by hydraulic transport. Between Phases 1 and 2, there was a delay of several weeks to allow for the installation of vertical wick drains and instrumentation. The first sandfill layer provided a platform strong enough to support wick drain installation machines. Vertical wick drains were installed all over the site. A dense grid of drains was installed in the Upper Clay layer. Drains in the Lower Clay were installed in a wider grid. By pumping water from the Middle Sand layer, the groundwater level has been lowered in order to cause temporary over-loading in the Upper and Lower Clay layers. A network of monitoring devices (including vibrating wire piezometers installed in boreholes, vibrating wire push-in piezometers, magnetic extensometers, settlement beacons and inclinometers) was installed on the site in order to monitor the settlement and hence consolidation behavior of the Upper and Lower Clays. Monitoring focuses on the settlement

progress (time aspect) as well as magnitude (compression aspect). Collected data allows for a comparison between predictions and true behavior including fine-tuning of the prediction model. Settlement model components included creep. Surface settlement is about 5 to 6 m during the site preparation phase.

Foundation design A settlement reducing piled raft solution was shown to be most economic for this site. Foundation loading is distributed by a combined raft foundation and floating piles.

Conclusions An innovative ground improvement scheme has been developed by Fugro to achieve the necessary ground improvement of the weak foundation soils. By adopting this scheme, a substantial reduction of the overall foundation costs is anticipated and limited plant foundation settlements are expected over the lifetime of the new Escravos GTL plant.

This solution became feasible in combination with discussed settlement accelerating measures and consequent improvement of soil properties. Foundation piles will be installed into the Lower Clay: there is no need for longer piles embedded into the basal dense sand. Although the pile tips are in clay, secondary/creep settlements of the raft foundations are minimal. Negative skin friction was also accounted for in detailed foundation design.

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Delft Cluster: working on the sustainable development of densely populated delta areas Dr. Jurjen van Deen, senior specialist, GeoDelft

Delft Cluster P.O. Box 69 2600 AB Delft The Netherlands Tel. +31-(0) 15 269 37 93 E-mail: info@delftcluster.nl Internet: www.delftcluster.nl

Delta areas all over the world are attractive places to live and work. However, although they have tremendous economic potential, the inhabitants also live in the permanent threat of flooding and subsidence of the soft soil. Civil and hydraulic engineering are key factors in managing these challenges and providing sustainable solutions. Six knowledge institutes in and near Delft, the Netherlands, have joined forces to form Delft Cluster. Delft Cluster is an open network, whose aim is to acquire, develop, distribute and apply their combined knowledge in this field. The six institutes have complementary capabilities, from geoengineering to hydraulics, from risk management to education. Other organisations - consultants, contractors and customers - can link up to the open network via projects. They also join in the steering of the research programme by membership of committees and co-financing the research. Delft Cluster aims to cover all the technical aspects of sustainable living in soft soil deltaic areas. The Delft Cluster programme is subdivided in six central themes related to water management, flooding risks, infrastructure, building and (underground) construction aimed at a safe, habitable and sustainable future society. One of the most challenging geotechnical aspects is how to

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ABSTR ACT Because of the enormous economic potential delta areas all over the world are attractive places to live and work. At the same time these low-lying areas are subject to subsidence of the soft soil and the inhabitants have to face the permanent threat of flooding. Civil and hydraulic engineering are key factors in managing these challenges and providing sustainable solutions. To cope the technical problems in the Netherlands, six knowledge institutes in and near Delft with complementary capabilities have joined forces to form Delft Cluster: an open network, whose aim is to acquire, develop, distribute and apply their combined knowledge in this field. The Delft Cluster research programme is subdivided in six central themes in relation to watermanagement, flooding risks, infrastructure, building and (underground) construction to maintain a safe, habitable and sustainable society in the future. One of the most challenging geotechnical aspects is how to accommodate the ever increasing pressure on the physical space by building underground structures within these soft soils. As an example of the Delft Cluster programme some results of the tunneling research are summarized.

accommodate the ever increasing pressure on the physical space by building underground structures within these soft soils.

The path to the future lies in the underground Apart from the constant threat of water on the one hand and the soft soil on the other, low lying delta areas in general, and the Netherlands specifically, face an additional problem as well. The claims on the available space in the Netherlands are becoming bigger and bigger. A solution to cope with this problem could be found in a totally new dimension: the underground. However, building underground

\ Figure 1 TBM front in GeoCentrifuge test

in these soft soils is not without risks when the available knowledge and experience is limited. Tunnels in Holland have been traditionally constructed by dredging a trench and sink down caissons in the trench. The impact on above ground activities is temporarily but large, and tunnel boring would be a viable alternative. However, the soft soil has long been an impassable obstacle, and only in 1999 the first large diameter bored tunnel in the Netherlands, the Second Heinenoord tunnel, was completed. From the beginning on it was decided that this tunnel should be a study object as well and this approach has been the beginning of a succesful knowledge development strategy. The design was based on experiences in Japan and Germany. During the construction an extensive monitoring program was performed [Bakker, 2001]. Unexpected effects occurred: the settlement trough was narrower and the soil and pore water stress distribution were quite different from what was expected based on the experience from dredging research.

Tunnel learning From this first experience it became clear that knowledge development was heavily needed. Delft Cluster, founded in 1999, decided to focus

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Delft Cluster: working on the sustainable development of densely populated delta areas

\ Figure 2 Numerical simulation of TBM front

on the fundamental long term aspects. Herein they could easily hook on to the running programme of COB, the Netherlands Centre for Underground Construction, which was directed primarily on applied research and development. The COB-programme was therefore a very relevant source of long term research questions, and the COB-approach of developing knowledge in one tunnel project and applying it in the next was adapted as a fruitful strategy. Several projects of the Delft Cluster programme have therefore been coupled directly to COB within the framework of ‘Joint Practical Research on Bored Tunnels’ (GPB). Coupling Delft Cluster research to practical projects guaranteed the availability of field

\ Figure 3 Temperature distribution during freezing

during construction of traverse #1 Westerschelde Tunnel

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laboratories. In that way it became possible to perform extensive measurements, but also to do experiments and to apply and validate the acquired knowledge and models. A clear example is the optimisation of the grouting process throughout a number of tunnel projects. In the Second Heinenoord tunnel it appeared that the subsidence of the surface area was quite sensitive to the amount and pressure of grout injected in the tail void of the TBM, and this generated a string of research projects in numerical and physical modelling [Talmon 2001, Brassinga 2001] and field verification [Bezuijen 2002]. During the construction of the Botlek railway tunnel GeoDelft and WL|Delft Hydraulics performed tests on a two component grout, and in the Sophia railway tunnel an extensive measurement and evaluation programme has been completed. By the knowledge developed in those cases, the grouting process can now be predicted accurately, so that the tunnel which will shortly be bored in the subsoil deep under the pile foundations of old Amsterdam can be looked forward with confidence.

Freezing A second example of a field laboratory in the framework of the GPB consortium was the Westerschelde tunnel. The construction of this 6.6 km long tunnel under the Westerschelde waterway experienced rather extreme conditions as the deepest point lies at 60 m below sea level. A number of transverse links, each with a length of 12 m, had to be constructed between the two bored tunnels. Their construction was done with help of soil freezing. It was the first time that this technology was used in the Netherlands on that scale in such an extreme condition. Delft Cluster partners GeoDelft and TNO-NITG (National Geologic Survey) cooperated in the research how and how much freezing of the surrounding soil would deform the transverse tubes [Rijkers 2002]. The results from this project will also benefit to other Dutch tunnel and other underground construction projects.

Tunnel structure Not only the effects on the surroundings but also the structure of the concrete tunnel itself is subject of the Delft Cluster research. In the Heinenoord case it already appeared that in the soft Dutch soil the behaviour of the stiff structure is fundamentally different from what the existing models predicted. Although

the models suggested that the construction phase is not indicative for the design conditions of the tunnel segments, it appeared to be of paramount importance. The stamps with which the TBM is pushed forward find their reaction forces in the already placed tunnel segments. Possible damage mechanisms to the segments were investigated in a full scale test set-up at the Technical University of Delft. Parallel to that, an extensive set of measurements has been performed during construction of the Botlek railway tunnel. The results of these tests have led to an optimized form of the segments and to modifications in the joints, notches and reinforcement of the segments. These examples show the power of combination of knowledge of the soil, of soil/construction interaction and of construction material properties, that has been accomplished in the Delft Cluster network.

References [1] K.J. Bakker, E.A.H Teunissen, P. van den Berg, M.T. Smits The Second Heinenoord Tunnel: the main monitoring results Proc. 15th Int. Conf. Soil Mech. Geotech. Eng., Istanbul, Aug. 2001, Lisse, Balkema, 2001, Vol.2, pp.1445-1450 [2] A. Bezuijen, A.M. Talmon, F.J. Kaalberg, R. Plugge Field Measurements on grout pressures during tunneling Proc. 3rd Int. Symp. Geotech. Aspects Underground Constr. Soft Ground, Toulouse, Oct. 2002, Lyon, Specifique, 2002, pp.113-118 [3] H.E. Brassinga, A. Bezuijen Modelling the grouting process around a tunnel lining in a geotechnical centrifuge Proc. 15th Int. Conf. Soil Mech. Geotech. Eng., Istanbul, Aug. 2001, Lisse, Balkema, 2001, Vol. 2, pp.1455-1458 [4] R.H.B. Rijkers, B.R. Hemmen, N.M. Naaktgeboren, H. Weigl Proc. 3rd Int. Symp. Geotech. Aspects Underground Constr. Soft Ground, Toulouse, Oct. 2002, Lyon, Specifique, 2002, pp.379-386 [5] A.M. Talmon, L. Aanen, A. Bezuijen, W.H. van der Zon Grout pressures around a tunnel lining Proc. Int. Symp. Modern Tunnelling Sci. Technol., Kyoto, Oct. 2001, Lisse, Balkema, 2001, Vol.2, pp.817-822

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Long-term behaviour of a bored tunnel partly lying in soft soils

H.E. Brassinga, H.M.A. Pachen, Engineering Department Rotterdam Public Works IGWR, The Netherlands O. Oung GeoDelft, The Netherlands; now working at Rotterdam Public Works IGWR A. Bezuijen GeoDelft, The Netherlands

Engineering Department Rotterdam Public Works IGWR P.O. Box 6633 3002 AP Rotterdam The Netherlands Tel. +31-(0) 489 66 21 E-mail: ingenieursbureau@gw.rotterdam.nl Internet: www.gw.rotterdam.nl

\ Figure 1 Mapped out metro line. Source: Aeroview.

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ABSTR ACT

Two bored single-track tunnel tubes with an outer diameter of 6.5 m each will be needed to build the 2.4 km long section of RandstadRail in the city area of Rotterdam. On several parts of the metro-route, the tunnel tubes lies partly in the soft Holocene clay and the stiff Pleistocene sand. During the lifetime of the construction, it is expected that the top of the soft Holocene layers will settle 1.5 m due to consolidation and creep. Therefore the tunnel lining will be increasingly loaded with time. The time dependent additional loading has been analyzed analytically as well as numerically. Physical modelling using the Delft geocentrifuge was performed in order to verify the design approach. The behaviour of the bored tunnel in the long-term has been asserted based on the results of the performed centrifuge tests and the findings of the finite element methods. Introduction RandstadRail is a future light-rail link between Rotterdam, The Hague and Zoetermeer in the Netherlands (see figure 1). Two single-track shield tunnels in Rotterdam are needed for its construction. Each tunnel has an outer diameter of 6.5 m and a length of 2.4 km, using a slurry shield TBM. Tunnelling will be performed in the Pleistocene sands over a substantial

part of the alignment. However, nearby the Station Blijdorp and the connections to the existing (metro- railway-) lines the overburden is very shallow and the lining is predominantly located in the soft organic clay layers. With time, clay will settle. For the design of the tunnel, it is of main importance to assure the predictions of the long-term interaction between the soil and the construction.

\ Figure 2 Soil profile at location.

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Long-term behaviour of a bored tunnel partly lying in soft soils

\ Figure 3 Extensometer measurements

\ Figure 4 Loading due to negative skin friction on a

bored tunnel (mechanism adopted from analytical modelling).

Ground conditions The geotechnical profile of the Rotterdam city area consists, starting from surface level (at 1 m above the reference level NAP), of a shallow top layer of anthropogenic sand, 15 m of soft Holocene layers (peat and organic clay), overlying the Pleistocene sand layer, which has a thickness of about 20 m. The water level is about two m below NAP, see figure 2.

Tunnel design The design is based on two single track tunnels with an internal diameter of 5.8 m each and a concrete lining of 0.35 m thickness. The lining consists of 7 precast concrete segments and one keystone. The segments have a width of 1.5 m. Each segment is provided with one constructive dowels and sockets to bridge the ring joints in order to reduce the deformation of the lining and therefore to secure the watertightness.

Long-term settlements During the design lifetime of the tunnel (100 years), the soft layers will settle due to consolidation and creep. A regular sand supply on ground level is necessary in order to maintain

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the surface at a fixed level. To study the settlement behaviour of the organic clay and peat layers, extensometer gauges were installed. Some results are plotted in figure 3. From the extensometer measurements and the levelling data of the manhole covers of the sewerage system in this part of the city over the past 20 years, it was concluded that a yearly settlement of 15 mm at the surface and 2 mm over the height of the tunnel is to be expected. The Pleistocene sand will not settle.

Forces on the lining due to long-term settlement Because the tunnel is a relatively stiff element, the forces in the lining will increase due to long-term settlements. The vertical force on the crest will exceed the vertical overburden pressure. The time dependent additional force, called negative skin friction, was analysed analytically assuming a linear stress strain relation. Using the stress distribution function of Airy, the vertical and horizontal additional stresses Δpv and Δph were determined (Pachen & van Zanten, 2002). For an embedment of 1350 (see figure 4) and a Poisson ratio of 0.33 the solutions are: (1) uo : vertical soil displacement at crest Eoed : constrained modulus of elasticity R : Radius of the tunnel

Geocentrifuge modelling In order to verify the analytical solution, two physical model tests were performed in the geocentrifuge at GeoDelft.

Test setup The model was built at a scale of 1:65. The model tunnel was made of an aluminum tube, placed in a strongbox and supported by an aluminum strip. The lower part of the tunnel was embedded in a dense sand layer (1350). The tube was instrumented. After placement of the tunnel in the sand, a layer of Spesswhite clay slurry (water content of 94 %) was applied. The first part of the centrifuge tests was selfweight consolidation of the clay. The thickness of the clay layer after the self-weight consolidation was 10 m at prototype scale in test 1 and 9 m in test 2. On the model tunnel, in the sand and in the clay layers, pore pressure and total stress transducers were installed. The front of the strong box consisted of a Plexiglas window, through which a grid, applied on the clay, was observed with 2 video cameras. After that self-weight consolidation had taken place in the geocentrifuge, a sand layer was applied on top of the clay in flight to generate an overburden pressure of about 55 kPa. After consolidation, a second layer of sand was applied with the same thickness leading to further consolidation. In the second test, a sand layer of 1.3 m (prototype scale, 0.02 m in the model) was applied at the start to increase the stress level in the clay with ~13 kPa. The tests were performed in saturated conditions. As in the first test also two extra sand layers were applied after self-weight consolidation. Since creep effects can not be scaled in a centrifuge test, these tests are only valid for effects on the tunnel due to primary consolidation. In the tests, the deformation pattern influenced by wall effects at the glass wall, if any noticeable, was investigated. Some coloured spaghetti were put through the

\ Figure 5 Deformed grid after test 2 (left). Deformation of clay around the tunnel as determined by image processing

(right). The dot is the original position, the end of the line the position at the end of the test.

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Long-term behaviour of a bored tunnel partly lying in soft soils

\ Figure 7 Test 2: Measured surface settlements during

the test just above the tunnel and 220 mm next to the tunnel axis (model dimensions) (settlements deter-

\ Figure 6 Test 2: Measured soil stresses on the tunnel and in the clay at 220 mm from the tunnel axis (model dimensions).

clay layer from the backside to the glass wall before testing. After the test, it was found that the spaghetti were still straight, indicating that wall effects had only little influence on the results. Test results In figure 5, the deformation of the clay at the end of the consolidation after that the first sand layer (test 2) was applied, is shown. Figure 6 shows the measured vertical soil stresses during the test at the crest of the tunnel and at the same level in the clay at 220 mm from the centre of the tunnel. The vertical stress at some distance from the tunnel was calculated from the total stress transducers that were placed between the sand layer at the bottom of the model and the clay. The increase of the soil stress on top of the tunnel (Gt 3) compared to the stress in the clay (Gt 1) at some distance from the tunnel during the consolidation of the two sand layers shows how the presence of the model tunnel led to an extra increase in the total stress compared with the free field situation, the difference was approximately 140 kPa at the end of the test. It appeared that during primary consolidation both pressure gauges measured the same total stress, but after applying the sand layers the stress on top of the tunnel increases more than the stress in the clay at some distance from the tunnel. This indicates that during primary consolidation when the clay is still very soft the ‘negative friction’ hardly influences the result, but the influence increases as the clay has gained some stiffness. Surface settlements were a slightly less just above the tunnel compared to the settlements

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at 220 mm from the tunnel axis, see figure 7, but the difference is small. Deformations in the clay were measured using image processing. In figure 5, directions of the deformation around the tunnel were highlighted. It appears that, apart from the vertical deformation, there is horizontal clay deformation away from the tunnel axis in the clay above the upper fourth part of the tunnel and a horizontal deformation to the tunnel in the clay layer beside the tunnel.

FEM Calculation By means of a Finite Element Method (FEM) model, the test results were analysed. In the numerical model both self-weight and primary consolidations after applying the two sand layers were simulated. The soil model used was the Plaxis Hardening Soil Model (HS; see Brinkgreve et al.). The material parameters were determined from Constant Rate of Strain (CRS) oedometer tests and CU triaxial tests on samples of the Spesswhite slurry. Figure 8 shows the contour lines of the deformations as calculated with the FEM model and the deformation increments in the FEM mesh, after application of two sand layers and the followed consolidation. When the deformation pattern of the FEM-calculations is precisely compared with the findings of the centrifuge measurements, see figure 9 and figure 8, it is evident that the negative skin friction mechanism of the numerical and physical modelling is quite similar. Figure 9 shows the measured and calculated total radial stresses on the upper part of the tunnel (test 2). The stresses coincide rather well. The differences between calculation and

mined from video images).

measurement are explained by the rigid (aluminium) support strip under the model tunnel. The calculated effective radial and shear stresses around the tunnel were used to determine the vertical (Δpv) and horizontal components (Δph) of the additional stresses. In this way a comparison between the linear elastic solution (Eq.(1)) and the FEM-analyses could be made. From these calculations, it was concluded that Δpv decreases more or less linearly towards the outside of the tunnel. The horizontal component Δph increases approximately linearly from the axis to the top of the tunnel. This result contradicts the elastic solution where both Δpv and Δph result in constant values. Obviously, in the

\ Figure 8 Deformation of clay around the tunnel; con-

tour lines from FEM calculations (top) and increments from FEM calculations (bottom).

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Long-term behaviour of a bored tunnel partly lying in soft soils

• the effective surface load (submerged value); • the rate of embedment of the tunnel; • the stiffness ratio of the soil and the tunnel lining.

\ Figure 9 Measured (geocentrifuge) and calculated total

radial stresses (FEM-method) on the tunnel lining.

\ Figure 10 Vertical additional load Δp versus effective v

surface load for a variation of the soil stiffness Eoed and

a geometry in accordance with the geocentrifuge tests.

\ Figure 11 Vertical additional load Δp and settlement u v 0

for the location Station Blijdorp; elastic approach versus FEM scheme.

FEM-model, the soil arches on the stiff Pleistocene sand next to the tunnel. The relation between the soil stiffness Eoed and the additional load due to negative skin friction was determined from the numerical simulation of the geo-centrifuge tests. Results from calculations with a variation of 50 times Eoed are shown in figure 10. It was concluded that the negative skin friction (end of consolidation value) is independent of Eoed. As the vertical soil displacement at crest u0 is directly related to Eoed, this is in agreement with the elastic solutions of Eq.(1), except for the factors given. For a specific geometry the negative friction can be regarded as only dependent on:

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Practical application Using the FEM Plaxis scheme, the vertical component of the negative friction was determined at the location of the Blijdorp Station. The ground conditions of this location and details of the lining properties have been given previously. The additional vertical stress was calculated as a function of the settlement u0 of the undisturbed clay at crest level. For the results see figure 11. Evidently, the negative friction is not limited by full plasticity in the calculated range. The difference with the elastic solution increases with increasing settlement over the height of the tunnel.

References [1] Pachen, H.M.A., van Zanten, D.C. van, 2002 Prediction of long term behaviour of a bored tunnel in soft soil. Proc. Sec. Int. Symp. On Geotech. Aspects of Underground Constructions in Soft Ground Toulouse, Balkema; Rotterdam [2] Pachen, H.M.A. & Brassinga, H.E. & Bezuijen, A., 2003 Geotechnical centrifuge tests to predict the loading conditions on a bored tunnel due to consolidation settlements. ITA Proc. (Re)Claiming the Underground Space Amsterdam, Swets & Zeitlinger Lisse. [3] Brinkgreve, R.B.J. et al., Plaxis 2D version 8, Balkema; Rotterdam.

Conclusions When tunnel tubes are located at the transition zone of soft to stiff soil layers, long-term settlements of the soft soil layers lead to additional loads on the tunnel lining. As expected, the additional loads affect the vertical effective stresses on the tunnel lining. The study revealed that a change of the horizontal stresses has to be accounted for as well. The analytical linear elastic approach according to the stress distribution function of Airy (see Eq.(1)) appears to be conservative. A more sophisticated elasto-plastic soil model is needed to simulate the centrifuge tests. With the finite element approach, using the Plaxis Hardening Soil model, the centrifuge test results can be simulated well. The difference with the elastic solution increases with increasing settlement (see figure 11). The negative skin friction force at the end of the consolidation phase appears independent of the soil stiffness. When the stiffness increases, the deformation around the tunnel decreases but the rate of soil loading increases. For a given soil stratification and designed tunnel dimensions, the end of consolidation value of the negative skin friction loading depends only on the effective surface loading. A plastic upper boundary of the negative skin friction was not found, neither in the geocentrifuge tests nor in the numerical simulation with the finite element model. The additional loading on the lining increases nearly linear with the long term settlements due to consolidation and creep and therefore the tunnel loading increases steadily in time.

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Designing reinforced embankments on piles: publications in Osaka M. Nods Huesker Synthetic

HUESKER

Agent voor Nederland

HUESKERCECO B.V. P.O. Box 1262 D-48705 Gescher Germany Tel. 0049 2542 7010 E-mail: info@huesker.de Internet: www.huesker.com

publications in Osaka Two important papers related to reinforced embankments on piles and design methods were published at the 16th International Conference on Soil Mechanics and Geotechnical Engineering (ICSMGE) in Osaka (2005): 1. Piled embankments: Overview of Methods and Significant Case Studies, by Alexiew; 2. Embankment project on soft subsoil with grouted stone columns and geogrids, by Heitz, Kempfert and Alexiew.

ABSTR ACT

Two important papers were published at the Osaka conference addressing design and application of geosynthetic reinforced embankments on piles. The availability of design procedures and reference embankments for high speed trains indicate that the system of piled embankments has reached the stage of maturity. The availability of high strength geogrids with different polymers allows for project optimisations.

The first paper (Alexiew) is reporting on different analytical design procedures which are in use in various countries world-wide, while the second paper (Heitz a.o.) is addressing a specific railway embankment project. Also in Holland the discussion on design procedures is ongoing, as can be read in the regular edition in the Dutch language of Geotechniek No 3, 2005 (page 17). A CUR working group is planning to address the issue of design methods and arching effects, and to develop design guidelines. Alexiew’s publication can be an interesting contribution to the discussions in the CUR working group.

Advantages of piled embankments Important advantages of piled embankments as compared to “conventional” embankment foundations directly on the soft soil are: • No consolidation time required, direct use is possible; • No settlements, no maintenance costs; • No import/export of additional embankment fill for soil improvement, settlement compensation, etc; • No major influences on existing underground structures (foundations, cables, sewage systems etc.) and geohydrology.

\ Figure 1 Influence of the polymer used on the tensile

force-strain behavior of Fortrac® geogrid “families”

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Despite the ongoing discussions on design procedures Alexiew concludes that reinforced embankments on piles as a system have reached the stage of maturity. A lot of experience is available in design procedures, construction and (registered) behaviour. A range of geosyn-

thetic reinforcements with different polymers (see figure 1) is available today, which eliminates any limitation for their use in such systems. Efficiencies are possible by maximising pile spacing and using stronger reinforcements in one or two layers. Fortrac® geogrids with strengths up to 2000 kN/m are possible these days. Typically the additional costs for stronger reinforcements are negligible in relation to possible reconstruction costs, therefore it is recommended that in case of any doubts regarding bearing capacity or serviceability in the stage of design, to use stronger reinforcements. Some failed or highly deformed structures are known, which were due to optimistic design assumptions. Alexiew also presented some specific project examples.

New German design method in EBGEO The development of the new German design method started in 1995. Focal points were to improve the stress redistribution model for the embankment body and to find a way for a reasonable consideration of a possible upward soft soil counter pressure between the piles. The draft for a new chapter in EBGEO (Empfehlungen für Bewehrungen aus Geokunststoffen - DGGT) is ready. It includes a new “multi-shell arching” theory and a strain-related counter pressure. Only one or maximum two strong reinforcement layers directly over the piles are recommended. Because the soft soil counter pressure is of great influence on the results (reinforcement tension), caution is advised in

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Designing reinforced embankments on piles: publications in Osaka

\ Figure 2 New German design method for piled embankments

the actual use of counter pressure in design calculations. Lowering the ground water level could already eliminate all counter pressure.

Projects examples Recent project examples presented in Alexiew’s paper include a motorway embankment in the UK (A63 Selby Bypass, 2003) and a railway embankment in Germany (Büchen, 2003, high speed rail link Berlin-Hamburg). Both projects are examples of optimisations via creative engineering with non-standard Fortrac® geogrids (individual custom-made product solutions with different polymers) which are unique possibilities offered by Huesker Synthetic.

ICE Railway Embankment Paulinenaue: a site of superlatives The second paper by Heitz a.o. is presenting a specific railway embankment project in the section Berlin-Hamburg (13 km section near Paulinenaue). In Geokunst of April 2005 (Supplement in the regular edition in the Dutch language of Geotechniek No 2, 2005) this project was presented in more detail. It concerned upgrading of the 150 year old railway line between Berlin and Hamburg for the ICE high speed trains with maximum speeds of 230 km/h. An earlier reconstruction at the end of the 90s resulted into allowed train speeds of 160 km/h. In terms of construction, the greatest challenges to overcome were on a section between Paulinenaue and Friesack. The boggy ground there is capable of taking very little load. In the earlier construction stage, the rail embankment had been founded

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\ Figure 3 Paulinenaue section. Three layers of PVA Fortrac® geogrid were placed at

300 mm vertical spacings

on 40,000 partially injected vibro columns (PIVC) and geogrid reinforcement. During the planning phase, DB Projektbau GmbH was at first in favour of a partial closure with single track operation, as had been adopted in other sections. In order to ensure that this demanding and high quality project was executed in the best possible manner, a decision in favour of a specified period of full closure was made in consultation with the joint venture partners. Exactly 76 days were allowed for this to take place in summer 2003. A seven-day week, three-shift working system was introduced so that the Herculean task could proceed smoothly all around the clock. The job was planned down to the smallest detail before construction began. Work on the section started simultaneously at several sites. First the existing track bed, along with the associated groundworks was completely removed. The original boggy ground was then replaced to the level of the groundwater table. Approximately 1 m of the partially injected vibro columns forming the piled foundations was then exposed and cut off to existing ground level. Their condition was recorded and repairs carried out where necessary. The new embankment was then constructed on this foundation. The first geogrid layer was placed over a 200 mm layer of graded aggregate. Then followed three layers of Fortrac® PVA geogrid type R 200/200-30 M placed at intervals of 300 mm. The 14 m wide rolls of geogrid were placed transversely to the track and overlapped by one metre. Each layer of geogrid was precisely installed to laser accuracy and tolerances of less than 10 mm, in accordance with the manufacturer’s recommendations. Huesker

manufactured the custom-made geogrid in 210 m long rolls. This kept waste to a minimum. For the critical construction phase – the time of full closure – Huesker had reserved additional capacity at its production plants to ensure that extra geogrid could be supplied very quickly if required. Both papers can be requested via info@huesker.de.

Huesker Synthetic: one of the worlds leading manufacturers of custom-made reinforcing geosynthetics Over the past 40 years, Huesker has developed a wide range of products for use in the construction industry. The high quality products are manufactured and certified in accordance with ISO 9001 and are CE compliant. Ongoing liaison with contractors, consultant engineers and research institutions enables Huesker to continually modify and improve products to meet the growing and varied needs of worldwide customers. Huesker’s highly qualified and experienced technical team can offer design advice and engineering solutions on a variety of construction applications including: • Road, Rail and Airport infrastructure • Hydraulics in river, marine and port engineering • Ground improvement and foundation engineering • Waste disposal and contaminated land reclamation Further information can be found at www.huesker.com.

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Influences of Physical Grout Flow around Bored Tunnels S.J. Lokhorst, C.B.M. Blom, B.M.A. Slenders, E.A. Kwast Holland Railconsult

Holland Railconsult P.O. Box 2855 3500 GW Utrecht The Netherlands Tel. +31-(0) 30 265 55 55 E-mail: info@hollandrailconsult.nl Internet: www.hollandrailconsult.nl

Introduction After the construction of the first shield driven tunnels in the Netherlands it was concluded that the construction stage of bored tunnel linings is as normative as the serviceability stage [1,2]. It was found that in the construction stage the concrete strains and the

ABSTR ACT The behaviour of the grout layer during the construction of bored tunnels is one of the determining factors for the stability and deformations of the tunnel structure and the surrounding soil. A new calculation model is presented which incorporates the relevant properties of and the interactions between soil, grout and lining. With this model the influence of different grout strategies on structural safety of the tunnel, surface settlements and plastic deformations in the soil can be analysed. The model was applied successfully to the Green Heart Tunnel in the Netherlands.

deformation of the tunnel lining could exceed the predicted values for the serviceability stage and that settlements deviated from expected values. Much effort has been put into research to understand the phenomena causing this normative construction stage. The construction process of a bored tunnel is

\ Figure 1 Tunnel boring machine, segmented tunnel lining and grout layer.

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a continuous process. The tunnel boring machine (TBM) excavates the soil at the front and pushes itself forward using hydraulic jacks positioned against the already built tunnel lining at the back (see figure 1). The excavation is stopped periodically to allow for the erection of segmented rings inside the TBM. The difference between the external diameters of the TBM and the lining causes a gap between the soil and the lining at the tail end of the TBM. This gap is filled with grout while the TBM progresses. The behaviour of the grout layer is supposed to play a dominant role in the deformations of the tunnel lining and the surrounding soil during the construction stage. The function of the grout is twofold: 1 The grout enables the embedding of the tunnel in the surrounding soil; 2 The grout prevents large deformations of the surrounding soil and settlements at the surface. Usual basic components of grout are binders (cement), sand and water. The composition however will vary per project and/or per contractor and may be a well kept secret. The grout is locally injected at the tail of the TBM. During injection the grout leaves the nozzles as a fluid and flows around the circumference of the lining. After injection begins the hardening phase ranging from very fast (e.g. almost immediately in case of a two component grout) to very slow (several weeks). Depending on the progress of the TBM the

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Influences of Physical Grout Flow around Bored Tunnels

extent of the hardening stage of the grout near the TBM may vary considerably along the tunnel axis. The influence of grout in the construction stage on the lining and on the soil is generally studied separately: i.e. from geotechnical point of view or from structural point of view. Both approaches struggle with the same problem: the grout load and the grout support on either soil or lining. In this article a calculation model is presented where lining, grout and soil are combined and the grout is modelled explicitly as a physical layer with material properties. The grout layer is assumed to be a paste with both flow and viscoplastic properties. These properties allow the grout to flow in the gap between lining and soil. This model, which is called the SPARTA Grout model, is described below. The model was applied to a practical case and the results of grout pressure calculations were compared to on site measurements. The observed trends in the behaviour of lining and soil related to the grouting strategy are discussed.

sparta grout model Model description The SPARTA Grout model has been developed by Holland Railconsult and CST [3]. With this model the stresses and deformations in the tunnel lining, the grout layer and in the surrounding soil can be calculated using different grout fill ratios and different grout material parameters. The model is a two-dimensional model of the tunnel cross section surrounded by a grout and a soil medium. The requirement of the vertical equilibrium of the tunnel cross section is the basis of the calculation procedure. The model initially assumes an equally distributed grout layer around the lining. In this initial situation, generally, there is no vertical equilibrium. Equilibrium will be found due to grout flow, vertical displacement of the tunnel (uplift) and deformation of the soil, of the lining and of the grout layer. FEM characteristics The model is based on the FEM package ANSYS. The model has three regions, i.e. soil, grout and lining, and two interaction surfaces, i.e. groutsoil and grout-lining. The lining consists of concrete segments, with interaction surfaces between the separate segments. The grout layer surrounding the concrete lining is

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\ Figure 2 Calculated and measured radial grout pressures along the perimeter of the tunnel lining. The three continuous

lines in the graph represent the calculated grout pressures distributions at 90, 100 and 110% grout fill ratios. The dots

are the measured grout pressures on the five instrumented rings. The dashed line is the radial water pressure.

modelled as an isochoric viscoplastic material necessary for a curing paste. The isochoric behaviour is used to model the fluid character of the paste, while the viscoplastic behaviour is used to model the solid character of the paste. For each soil layer elastic and plastic material properties are defined. For the elastic material properties the E50-values of the separate layers are used as modulus of elasticity. The Poisson ratio is calculated from the K0 values of the separate layers. For the density of the soil only the effective density is used. For the plastic material properties the cohesion, the internal friction angle and the dilatancy angle of the separate layers are adapted for use in a DruckerPrager plasticity model, to have the same yield load as the more general Mohr-Coulomb plasticity model under plane strain conditions. The interaction surfaces between the grout and the soil, and the grout and the lining are defined as having cohesion contact and sliding capabilities. Validation The applied soil model is based on the DruckerPrager yield criterion. This criterion uses the “outer-cone-law” of the Mohr-Coulomb criterion. However, the model also allows the use of the “innercone” approximation, as well as the “plainstrain” or the “equalvolume” approximation. For testing the correctness of the four approximations a validation with the FEM-package PLAXIS was carried out. It was found that the general behaviour of both models confirmed each other. Similarities were

observed for soil stresses as well as deformations. Thus the application of the Drucker Prager yield criterion proved a reliable approximation for this model. Calculation strategy In the SPARTA grout model the followed order of calculation steps is: 1 Determine the initial soil stress distribution; 2 Excavate the soil due to the boring process of the tunnel; 3 Activate the lining and the grout layer; 4 The soil is allowed to relax (deform) until the initial grout thickness given by the user; 5 Calculate the force equilibrium of the soil layers, the grout layer, the concrete lining and the water pressure; 6 Increase the grout volume from the initial value in several steps to the final value and recalculate the force equilibrium in each step; In the calculations presented here the grout volume is gradually increased from 90% to 110% where 100% means that the theoretical void between the lining and the excavated soil is filled completely.

Grout pressure distributions The SPARTA Grout model was applied in a practical case at the Green Heart Tunnel in the Netherlands. In this tunnel project grout pressure distributions around the tunnel were measured in an extensive measurement program. The results of the grout pressure mea-

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Inuences of Physical Grout Flow around Bored Tunnels

\ Figure 3 Structural safety of the lining as a function of the grout fill ratio (presented is

a relative way).

surements presented in this article are made available by the HSL South organisation and by the Centre for Underground Research (COBF512). In five consecutive rings, grout pressures were measured using pressure cells cast in the concrete segments. The pressure cells were distributed over the perimeter of the lining. Figure 2 shows the results of both the measured and the calculated radial grout pressures. The vertical axis of the graph represents the grout pressure. The horizontal axis represents the perimeter of the tunnel (rotation angle). Note that the grout pressures from the left and right side of the tunnel are projected on one side only. The results of the calculations are given for three grout fill ratios (90%, 100% and 110% of the theoretical grout layer thickness of 250 mm). A shear yield stress of the grout of 1,5 N/mm2 is used. In the calculations the geometry and properties of the lining, the geotechnical profile of the soil and the properties of the individual soil layers at the location of the measurements (km 25,4) were accounted for. At this location the centre of the tunnel is approximately 27 m below surface level. In figure 3, the ground water pressures are shown as well. The pressure at the centre of the tunnel is estimated at 250 kN/m2. The gradient over the tunnel height is assumed to be hydrostatic (N.B. the cosine shape is the result of the tunnel perimeter on the horizontal axis). The comparison between the measured and calculated grout pressures indicates that the magnitude of the pressures can be predicted quite well. Also the gradient of the grout pressures agrees rather well with the gradient in the measurement.

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\ Figure 4 Vertical effective stress distribution in the soil for a grout fill ratio of 100%

These conclusions provide sufficient confidence that the other results of the SPARTA Grout calculations i.e. soil stresses, lining stresses, lining deformations etc. can be used to evaluate the structural safety of the lining, the embedding of the tunnel in the soil, and the surface settlements. In the next sections trends observed in the calculation results will be presented and discussed.

Tunnel lining behaviour In the model an interaction between grout and tunnel lining exists. For a grout fill ratio of 100% the calculation results show an upward displacement of the lining of approximately 5 cm. The shape of the ring remains almost round; the ovalisation of the ring is very small (0.2 cm of the radius). The tangential stress distribution in the lining confirms this: the stress gradients over the lining thickness are very small indicating hardly any bending. For both 90% and 110% fill ratios, however, large stress gradients are observed indicating ovalisation of the tunnel. It was found that for a fill ratio of 90% the tunnel has a lying oval shape and for a fill ratio of 110% a standing oval shape. The calculated stresses in the concrete lining can be transformed into normal forces and bending moments at each position in the ring. The combinations of normal force and bending moment can be used to determine a safety factor for the lining under the applied load case. Safety factors can be determined for both failure of the lining and for initial cracking. To estimate the safety factor of the lining here the combinations of calculated normal force bending moment in the ring will be compared to the concrete bearing capacity in the ultimate

limit state. The SPARTA Grout model predicts a high structural safety for the lining of the Green Heart Tunnel. For a 100% fill rate the minimal safety factor is 7.85. This value is used as a reference. These results are presented in a relative way in figure 3, in which the safety factor at a 100% fill rate is defined as 100%. As shown in figure 3, the tail void grout injection process clearly influences the deformations (ovalisation) of the lining. The 2-Dimensional character of the model implies that the beam action of the tunnel is not explicitly accounted for. The beam action originates from the transfer of vertical loads on one tunnel ring to the neighboring rings and/ or the TBM to establish equilibrium. In the SPARTA Grout model the uplift forces on a ring can only be counteracted by the resistance of the grout and the soil, the weight of the ring and the dead weight of TBM or inlay. The use of a fictitious weight of the tunnel, however, provides a good 2-D solution to study the influence of beam action on the soil-groutlining interaction.

\ Figure 5 Schematic representation of the vertical dis-

placements of the surface level and the perimeter of the excavated circle in the soil for a 100% grout fill ratio.

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Inuences of Physical Grout Flow around Bored Tunnels

Soil deformations Due to the tunnel boring process i.e. the excavation and the grout injection, the soil around the tunnel deforms. As a consequence the stresses in the soil will change. The changes of the vertical stress distribution in the soil are clearly visible in figure 4. In the graph, colours indicate the stress levels. At the left and right of the graph the original vertical stress distribution is still visible in the figure. Around the tunnel however the stress pattern of horizontal layers is disturbed. The disturbance is such that -except at the crown of the tunnel- the soil stress around the tunnel has decreased. For the horizontal stress distribution a similar decrease of stresses is found. As a result of the changes in the horizontal and vertical stress around the tunnel the stability of the soil may decrease and plastic deformations may occur. The plasticity can influence the stiffness of the support of the tunnel. For the case in view the effects on the stability were small en very local.

At the crown of the tunnel the soil moves upward whereas at the surface the soil moves downward. This will be the effect of a softening in the soil due to changes in the vertical and horizontal stress pattern. The resistance of the soil acting on the tunnel is generated at the shoulders of the tunnel in zones in the soil at an angle of 45 0 directing towards the surface. The results presented here agree very well with the results of the research by Nakken [4]. Nakken used the soil dedicated package PLAXIS to study the effect of grouting strategies on soil and lining. Although the ovalisation of the ring is very small (0.2 cm, as mentioned), figure 5 implies an ovalisation of (7-4)/2 = 1.5 cm of the border of the excavated circle in the soil. This means that the shape of the gap between lining and soil has changed and a considerable amount of grout has moved (flowed) to the bottom of the tunnel.

The influence of the grout injection will also be visible in the surface settlements. The settlements can be deduced from the results of the vertical displacements of the soil around the tunnel. A summary of the displacements of the surface level and the border of the excavated circle in the soil is given in figure 5. Such a diplacement pattern may explain the occurrence of settlements troughs steeper than expected.

Conclusions and perspective The SPARTA Grout model combines three components of bored tunnels (soil-groutlining) and their interfaces in one model. The model focuses on the solid and fluid properties of the grout layer and their influence on both the tunnel lining and the surrounding soil. The model was applied to a practical case of the Green Heart Tunnel. From the comparison between the measured and calculated grout

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pressures it was concluded that the magnitude and the gradient of the grout pressures could be predicted quite well. The SPARTA Grout model is able to explain the trends in the behaviour of the tunnel lining and the surface settlements during construction as observed in practice. The model also enables the evaluation of different grouting strategies in order to minimise lining deformations and/or surface settlements focused on the projects interests.

References [1 ] Blom, C.B.M. et al..; Montagespanningen maatgevend bij ontwerp lining. (in Dutch); Cement 10, oktober 1998. [2] |Blom, C.B.M. et al.; 3-Dimensional Analyses and Design of Tunnel Linings at the Construction Stage; Proc. 4th European Conf. On Numerical Methods in Geotechnical Engineering, Udine, October, 1998. [3] Blom, C.B.M.; 2D-Soil-Grout-Lining Model: SPARTA Grout, General Notification; January 2004; Holland Rail-consult, The Netherlands. [4] Nakken. D., Blom, C.B.M. & Bakker, K.J. Excessive Grout Pressures around the Lining of Shield Driven Tunnels in Soft Soil. Proc. International Symposium on Numerical Models in Geomechanics. NUMOG IX; Ottawa, Canada; August 2004; Balkema.

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GeoDelft: balance between theory and experiment Dr. Jurjen van Deen Senior Specialist GeoDelft

GeoDelft P.O. Box 69 2600 AB Delft The Netherlands Tel. +31-(0) 15 269 35 00 E-mail: info@geodelft.nl Internet: www.geodelft.nl

In forthcoming years a global climate change will cause sea level rise and increasing river run offs. For the densely populated and economically important areas in the low lying regi-

ABSTR ACT

In forthcoming years a global climate change will cause sea level rise and increasing river run offs. For the densely populated and economically important areas in the low lying delta regions of the world this forms an increasing threat. This certainly applies for the low lying Netherlands, with the European mainports Amsterdam Airport Schiphol and Rotterdam harbour. To cope the future flooding threats, geo-engineering will become a more important discipline. Being the national Netherlands’ expertise centre for geotechnics, GeoDelft is responsible for the knowledge management and dissemination in the field of geo-engineering. For generation of new knowledge a sound balance between field tests, physical modelling and theory development is a necessary prerequisite. The successful application of all three essential components is illustrated with an example of technological dike innovation

ons of the world this forms an increasing threat. As water problems are generally solved by soil -dikes and dams- geo-engineering is an increasingly important expertise. Of course, for the low lying Netherlands, with the European mainports Amsterdam Airport Schiphol and Rotterdam harbour, this is especially the case. Being the national Netherlands’ expertise centre for geotechnics, GeoDelft is responsible for the knowledge management and dissemination in the field of geo-engineering. One of the corner stones of the vision of GeoDelft is that a sound balance between field tests, physical modelling and theory development is a necessary prerequisite for fruitful knowledge development. GeoDelft therefore maintains a number of experimental test facilities among which the GeoCentrifuge. The fruitful cooperation between the three building blocks is illustrated on an example of technological dike innovation.

\ Figure 1 Validation of Van-model by FEM-calculations

and centrifuge tests

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In 1984 a dike section in the Netherlands collapsed during reconstruction works, fortunately not at a moment of high water level. The mechanism that had only seldom been reported before, appeared to be an uplift mechanism. It occurs mainly in tidal river basins where deep sandy layers are in direct hydraulic contact with the river. The uplift failure mechanism is

caused primarily by a loss of shear strength at the bottom of impermeable top layers of peat and clay covering the sandy underground. High water pressures due to the water level in the river lift the low weight layers, causing an extended horizontal failure plane at the interface of sand and peat.

Raison d’être of model testing The failure led to a model formulation based on first principles of force equilibrium. During the following years the model appeared to be inaccurate and difficult to apply. Therefore a second generation of uplift model, the so-called Van-model was developed. The methodology of this model is based on Bishop’s method and was in first instance validated by FEM calculations (Van 2001)( figure 1). Of course real world testing of failure of dikes is generally not practical. Here the first essential reason for model testing appears: testing of situations near failure and research on failure mechanisms. As the geometry of the dike structure is crucial for the development of the failure mechanisms it was necessary to use a scale model instead of just performing element tests. In order to model the material behaviour of soil correctly it is than necessary to incorporate the self weight effects of the structure. By

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GeoDelft: balance between theory and experiment

\ Figure 2 Test set up location Bergambacht

centrifuge testing the gravity is increased artificially to the level in accordance with the geometric scale factor; this is the essential reason to apply centrifuge testing. In the GeoCentrifuge tests of the uplift mechanism the Van-model appeared to give accurate results. In that phase of the research cycle, a unique opportunity popped up to perform a field test on a real dike. Part of a 800 year old dike along the river Lek near Rotterdam had become redundant due to a realignment of the river ( figure 2). After construction of the new dike, the old dike could be brought to collapse at the polder side. This was accomplished by placing a sheet pile wall at the river side, forming a ‘box’ with the old dike as the fourth wall, and filling this box with water six weeks in advance of the real test in order to get an equilibrium freatic line in the dike. Besides that a number of infiltration wells were installed in order to increase the water pressure in the deep sandy layer to such a level that uplift of the area behind the dike would occur. The location had been instrumented extensively with pore pressure meters, tensiometers, inclinometers and deflectometers as well as surface deformation measurements. During the preparation of the field test it appeared that the dike and the subsoil were much more inhomogeneous than had naively been expected. In a 5000 years old river basin the subsoil consists of highly irregular structures of sandy channels, and peat and clay layers and lenses. Also a 800 years old dike has during the years been constructed from highly varying material generally coming from nearby. Here a further advantage of model tests over field tests becomes clear. In model testing the circumstances can be chosen and controlled and a series of comparable experiments with different, known parameter values can be performed.

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The first field test did not lead to a collapse but after some modifications the test finally succeeded two months later (for details, see Koelewijn 2003). Both tests, the first without collapse and the second with collapse, generated a wealth of information. This was mostly due to a very well designed instrumentation plan based on a systematic risk based approach, balancing costs and additional information in a rational way (Hermes philosophy). This philosophy had been developed within another research framework and here a different line of theory entered the research program. The points of advantage of a field test, provided that the instrumentation is thoroughly thought over, are clear. The measurements are in the real world situation with real world inhomogeneities. Moreover, scaling effects that unavoidably affect scale model tests (e.g. because the grain size of the sand or the internal structure of organic clay is generally not scaled down) are absent. The combination of both can validate the numerical model really, and it generates a creative tension for further developments of the model. \ Figure 3 Failure mechanisms without doweling (A) and

Practical application During the research on the uplift phenomena, ideas were developed on how to remediate the problem. The most straightforward approach is to apply a broad embankment at the polder side of the dike. The extra weight of this earth structure prevents uplift at the most critical location just behind the dike toe. However, this type of intervention has large consequences for the built environment. At many places in the Netherlands houses have been built closely behind the dike, and they need to be demolished if an embankment is to be made. An alternative solution is driving long, anchored sheet piles between dike and house, but this is a rather expensive solution. From the uplift research the insight was gained that the primary effect of a sheet pile was actually to inhibit sliding of the soft layers over the sandy subsoil. It was therefore proposed to insert a sheet pile over only a limited depth range, like a dowel in the sand/peat interface. Such a structure is much cheaper due to the limited length and the absence of anchoring. This idea was tested and a design calculation model was validated again in a GeoCentrifuge experiment. It appeared that the short sheet pile increased the stability against uplift substantially and changed the failure mechanism (at much higher load) to a shallow one (Eekelen

with doweling (B). In the inset pore pressure development during repeated ‘storm surge’.

2003). The cost reduction with respect to standard sheet piles is about 1 million dollars per km dike. It is a clear example of how systematic research with theoretical and experimental input both, may lead to substantial financial and societal profits.

References [1] S.J. van Eekelen, M.A. Van, H.J.A.M. Teunisen and A.P.C. Rozing, Short sheet piling in dikes In: Proc. BGA Int. Conf. Foundations, Dundee, Sept. 2003, London, Telford 2003, pp. 895-904 [2] A.R. Koelewijn and M.A. Van., Monitoring of the test on the dike at Bergambacht: design and practice, In: Proc. 13th Eur. Conf. Soil Mech. Geotech. Eng., Prague, Aug. 2003, Prague, CGTS, 2003, Vol.1, pp. 755-760 [3] Van, M.A., New approach for uplift induced slope failure., In: Proc. 15th Int. Conf. Soil Mech. Geotech. Eng., Istanbul, Aug. 2001, Lisse, Balkema, 2001, Vol.3, pp. 2285-2288

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Your Partner in Risk Management

• SmartSoils®: soils on demand • Tunnelling in soft soil • Soil structures for water management • Sustainable infrastructure on soft soil

Delft Cluster partner

GeoDelft Stieltjesweg 2 2628 CK Delft P.O. Box 69 2600 AB Delft The Netherlands Tel +31 (0)15 269 35 00 Fax +31 (0)15 261 08 21 info@geodelft.nl www.geodelft.nl

• Geo-engineering solutions for environmental challenges As the Dutch knowledge institute for geo-engineering, GeoDelft's role is to obtain, generate and disseminate geotechnical expertise. The institute is an international leader in research and consultancy into the behaviour of soft soil and into soil-structure interaction in soft soil conditions. Research and Development at GeoDelft are based on the principle of the Innovation Cycle, with field testing, numerical calculations and validation by model testing taking place in a permanent feedback loop.

Dutch Institute for Geo-engineering

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