Experimental Study On Effect of Geogrid on Bearing Capacity Of Soil

By Ushandan Subramaniam

CHAPTER - 1 INTRODUCTION

1.1 GENERAL

Geogrids can be categorized as geosynthetic materials that are used in the construction industry in the form of a reinforcing material. It can be used in the soil reinforcement or used in the reinforcement of retaining walls and even many applications of the material are on its way to being flourished

The high demand and application of Geogrids in construction are due to the fact that it is good in tension and has a higher ability to distribute load across a large area.

Geosynthetics are used for reinforcement in many problem areas of civil engineering. A number of researchers have carried out theoretical and experimental studies to understand the role of reinforcement materials in improving the bearing capacity of foundation soils. Different studies have resulted in somewhat different specifications for reinforcement layouts. Experimental studies have been conducted to evaluate the bearing capacity of footings on reinforced sandy soil. These studies show that the reinforcement configuration values that give the maximum bearing capacity value depend on soil and footing types. In recent years, there have been many studies on this subject made a study presenting the use of artificial neural networks, and the multi-line a regression model to predict the bearing capacity of circular shallow footings supported by layers of compacted granular fill over natural clay soil. This study presents the laboratory model experiments of a surface strip footing on unreinforced and reinforced sand beds to investigate the effects of reinforcement length where the reinforcement length was chosen to be a multiple of footing

The data used in running the network models were obtained from an extensive series of field tests ,including large-scale footing diameters

1.2 OBJECTIVES

The main objective of the project is

• To study the behavior of strip footing in sandy soil.

• To study the strength characteristics upon geogrid on sandy soil.

1.3NEED FOR STUDY

• To determine the ultimate bearing capacity of a strip footing placed over granular and cohesive-frictional soils that are reinforced with horizontal layers of reinforcements.

• This will produce various adverse impacts on determination about effects on geogrids in sandy soil.

• It is required to determine the ultimate bearing capacity of a rough strip footing placed over a soil medium that is reinforced with a single layer.

Chapter 2

Literature Review

J Binquet, KL Lee - Journal of Geotechnical and Geoenvironmental …, 1975 trid.trb.org Results are presented for some 65 bearing capacity tests using a 3-in.(75-mm) wide strip footing on sand reinforced with strips of aluminum foil. Three foundation conditions are considered:(1) Uniform density sand to large depth;(2) sand overlying an extensive soft layer; and (3) sand overlying a potential cavern or localized weak pocket. The vertical spacing and concentration of reinforcing layers were varied to obtain the optimum arrangement for each condition.

J Binquet, KL Lee - Journal of Geotechnical and Geoenvironmental …, 1975 -

Laboratory data from some 65 small scale strip footing bearing capacity tests were used as a basis todevelopananalyticalprocedureforpredictingtheload-settlementandultimate bearingcapacity of a strip footing on sand which contains horizontal strips of tensile reinforcing. The theory is formulated in terms of the ratio of bearing capacity with and without reinforcing, aasuming that existing methods are adequate for predicting bearing capacities on sand with 0 reinforcing.

KH Khing, BM Das, VK Puri, SC Yen… - Geotextiles and …, 1994 – Elsevier A number of laboratory model test results for the ultimate bearing capacity of a surface strip foundation supported by a strong sand layer of limited thickness underlain by a weak clay with a layer of geogrid at the sand-clay interface has been presented. The tests were conducted at one relative density of compaction of sand and one undrained shear strength of clay. Two types of geogrid were used.

B Das, K Khing, E Shin - Transportation Research Record …, 1998 - trrjournalonline.trb.org The load-bearing capacity of a weak clay subgrade can be increased by placing a strong granular base course of limited thickness on top of the clay layer. The loadbearing capacity can be increased further, or the thickness of the granular base course can be reduced, by separating both layers by a geogrid. Laboratory model test results for the ultimate bearing capacity of a rigid strip loading on the surface of a granular soil underlain by a soft clay with a layer of geogrid at the interface of the two soils are presented

EC Shin, BM Das, VK Puri, SC Yen… - Geotechnical Testing …, 1993 - astm.org

Laboratory model test results are presented for the ultimate bearing capacity of a strip foundation supported by a saturated clay layer reinforced by layers of geogrid. The tests were conducted in one type of clay. The average moisture content of the clay was varied, yielding varying undrained shear strengths. Laboratory tests were conducted to determine the critical nondimensional values for the depth and width of the geogrid reinforcement layers and also the location of the first layer of geogrid

CR Patra, BM Das, C Atalar - Geotextiles and Geomembranes, 2005 – Elsevier

Laboratory model test results for the ultimate bearing capacity of a strip foundation supported by multi-layered geogrid-reinforced sand are presented. The depth of embedment of the model foundation, df, was varied from zero to B (width of foundation). Only one type of geogrid and one variety of sand at one relative density were used. The ultimate bearing capacity obtained from the model test program has been compared with the theory proposed by Huang and Menq,[1977. Journal of Geotechnical and Geoenvironmental Engineering.

BR Phanikumar, R Prasad, A Singh - Geotextiles and Geomembranes, 2009 – Elsevier

This paper presents data obtained from a series of laboratory plate load tests performed on geogrid reinforced sand beds. Fine, medium and coarse sands were used as test sand beds. Circular geogrids of diameter 120 mm were used as reinforcement layers. Improvement in load–settlement response was studied. The test sand beds were compacted to a relative density of 50%. A surface footing plate of diameter 60 mm was used as the shallow foundation.

VA Guido, DK Chang… - Canadian Geotechnical …, 1986 - NRC Research Press

Presented herein is a comparison of the results of laboratory model tests used to study the bearing capacity of geogrid and geotextile reinforced earth slabs. The parameters studied were the coefficient of friction between the geotextile and the soil, pull-out resistance between the geogrid and the soil, depth below the footing of the first layer of reinforcement, vertical spacing of the layers, number of layers, width size of a square sheet of reinforcement, and tensile strength of the reinforcement.

JP Sakti, BM Das - Transportation Research Record, 1987 - trid.trb.org

The ultimate bearing capacity of a model strip foundation resting on a saturated soft clay internally reinforced with geotextile layers has been investigated in the laboratory. The geotextile used for the study was heat-bonded nonwoven polypropylene. On the basis of the present test results, geotextile layers placed under a foundation within a depth equal to the width of the foundation have some influence on the increase of the short-term ultimate bearing capacity

PKBasudhar,SSaha, KDeb -GeotextilesandGeomembranes,2007 – Elsevier

The note pertains to an experimental study made on circular footings resting on semi-infinite layer of sand reinforced with geotextiles. Using the concept of homogenization of such soils, both analytical and numericalanalyseshavealsobeenconductedtopredicttheload-settlementbehaviorandcompared with experimental observations. The study highlights the effect of the footing size, number of reinforcing layers, reinforcement placement pattern and bond length and the relative density of the soil on the load-settlement characteristics of the footings.

JO Akinmusuru, JA Akinbolade - Journal of Geotechnical and …, 1981 . Results are presented of laboratory-scale bearing capacity tests using a 4 in.(100 mm.) square footing on sand reinforced with strips of a rope fiber material. Each layer of reinforcement was arranged in horizontal square grids. The addition of reinforcements increased the bearing capacity of the footing on the unreinforced soil by a factor which depended on the following: the horizontal spacings between strips on each layer, the vertical spacings between layers of reinforcement.

T Yetimoglu, M Inanir, OE Inanir - Geotextiles and Geomembranes, 2005 – Elsevier Abstract Laboratory California Bearing Ratio (CBR) tests were performed to investigate the load–penetration behavior of sand fills reinforced with randomly distributed discrete fibers overlying soft clay. The effect of fiber reinforcement content on bearing capacity, stiffness and ductility of the fiber-reinforced sand fill–soft clay system was determined. The test results indicated that adding fiber inclusions in sand fill resulted in an appreciable increase in the peak piston load.

RJ Fragaszy, E Lawton - Journal of Geotechnical Engineering, 1984 - ascelibrary.org Laboratorybearingcapacitymodeltestswereperformedonboth reinforcedand unreinforcedsand loaded by a strip footing. The effects of soil density and reinforcing strip length were investigated. The tests show that a significant increase in bearing capacity can be achieved at relative densities between 51 and 90% by the use of metal reinforcing strips. Bearing capacity of reinforced sand is a strong function of the length of the reinforcing strips only until the strip length reaches approximately seven times the footing width

CC Huang, F Tatsuoka - Geotextiles and Geomembranes, 1990 – Elsevier In order to develop a method of predicting the bearing capacity of horizontal sandy ground reinforced with tensile-reinforcement layers horizontally placed beneath a footing, a series of plane strain model tests with a strip footing was performed. The effects of the length, the arrangements and the rigidity and rupture strength of reinforcement were examined systematically. The strain fields in sand, the tensile forces in reinforcement and the distribution of contact pressure on footing were measured.

SK Dash, NR Krishnaswamy, K Rajagopal - Geotextiles and …, 2001 – Elsevier This paper presents the results from laboratory-model tests on a strip footing supported by a sand bed reinforced with a geocell mattress. The parameters varied in the testing program include pattern of geocell formation, pocket size, height and width of geocell mattress, the depth to the top of geocell mattress, tensile stiffness of the geogrids used to fabricate geocell mattress and the relative density of the sand

BM Das, MT Omar - Geotechnical & Geological Engineering, 1994 –SpringerLaboratory model test results for the ultimate bearing capacity of surface strip foundations on geogrid-reinforced sand and unreinforced sand are presented. A fine uniform sand and one type of geogrid (Tensar BX1000 (SSO)) were used for the tests. The width of the foundation and the relative density of sand were varied to determine their effects on the bearing capacity ratio. It was found that the bearing capacity ratio of the sand-geogrid system decreased with an increase in foundation width.

T Yetimoglu, JTH Wu, A Saglamer - Journal ofGeotechnical …, 1994 - ascelibrary.org

A study was undertaken to investigate the bearing capacity of rectangular footings on geogridreinforced sand by performing laboratory model tests as well as finite-element analyses. The effects of the depth to the first layer of reinforcement, vertical spacing of reinforcement layers, number of reinforcement layers, and the size of reinforcement sheet on the bearing capacity were investigated. Both the experimental and analytical studies indicated that there was an optimum reinfprcement embedment depth

KH Khing, BM Das, VK Puri, EE Cook… - Geotextiles and …, 1993 – Elsevier

Laboratory-model test results for the bearing capacity of a strip foundation supported by a sand layer reinforced with layers of geogrid are presented. Based on the present model test results, the bearing-capacity ratio with respect to the ultimate bearing capacity, and at levels of limited settlement of the foundation, has been determined. For practical design purposes, it appears that the bearing-capacity ratio at limited levels of settlement is about 67–70% of the bearing-capacity ratio calculated on the basis of the ultimate bearing capacity.

MT Adams, JG Collin - Journal of Geotechnical and …, 1997 - ascelibrary.org The potential benefits of geosynthetic reinforced soil foundations are investigated using large-scale model footing load tests. A total of 34 load tests were performed to evaluate the effects of single and multiple layers of geosynthetic reinforcement placed below shallow spread footings. Two different geosynthetics areevaluated:astiffbiaxialgeogridanda geocell.Parametersofthetesting program include the number of reinforcement layers, spacing between reinforcement layers, the depth to the first reinforcement layer.

MT Omar, BM Das, VK Puri… - Canadian Geotechnical …, 1993 - NRC Research Press Laboratory model test results for the ultimate bearing capacity of strip and square foundations supported by sand reinforced with geogrid layers have been presented. Based on the model test results, the critical depth of reinforcement and the dimensions of the geogrid layers for mobilizing the maximum bearing-capacity ratio have been determined and compared. Key words: bearing capacity, geogrid, model test, reinforced sand, shallow foundation.

EC Shin, BM Das, ES Lee, C Atalar - Geotechnical & Geological …, 2002 – Springer

Results of small-scale laboratory model tests to determine the ultimate bearing capacity of a strip foundation supported by sand with multiple layers of geogrid reinforcement are presented. Tests were conducted with only one type of geogrid and a sand compacted to one relative density. The embedment ratio of the foundation was varied from zero to 0.6. It is found that, for the given reinforcement-depth ratio, the bearing capacity ratio with respect to ultimate load increases with embedment.

NC Samtani, RC Sonpal - Journal of geotechnical engineering, 1989 - ascelibrary.org

Results of an experimental investigation into the bearing-capacity aspects of reinforced cohesive soils are presented. Undrained model tests are carried out on strip footings on unreinforced and reinforced cohesive soil. The reinforcements are in the form of ties that have been cut out from household aluminum foil. The reinforcement ties are placed only in the direction normal to the longitudinal axis of the footing. In this study, the length of the reinforcing ties and the spacing between them is varied

JH Yin - Geosynthetics International, 1997 - icevirtuallibrary.com In this paper, a new one-dimensional mathematical model is proposed for modelling geosynthetic-reinforced granular fills over soft soils subject to a vertical surcharge load. The geosynthetic reinforcement consists of a membrane (geogrid, or geotextile) placed horizontally in engineered granular fill, which is constructed over soft soil. The proposed model is mainly based on the assumption of a Pasternak shear layer. A new approach that consists of incorporating a deformation compatibility condition into the model is introduced

GG Meyerhof, AM Hanna - Canadian Geotechnical Journal, 1978 - NRC Research Press The ultimate bearing capacity of footings resting on subsoils consisting of two layers has been investigated for the cases of a dense or stiff layer overlying a weak deposit, and a loose or soft layer overlying a firm deposit. The analyses of different modes of soil failure are compared with the results of model tests on circular and strip footings on layered sand and clay soils.

3.1GENERAL

CHAPTER-3

Tests And Parameters

• The soil usually has the characteristics of low tensile strength and is highly dependent on environmental conditions.

• Reinforcement of the soil is specified as a method for improving the mechanical properties of the soil such as shear, compression, hydraulic conductivity and density. For soil reinforcement used of stone columns, soil nailing, micro piles and reinforced soil.

4.1 GENERAL

CHAPTER - 4

Methodology

The methodology of the experimental work described as shown in flow chart.

Review of Literature

Determination of bearing capacity

Tests on unreinforced system

Placement of geogrid reinforcement reinforcement

Tri axial compression test

Tests on single reinforcement system

Test on double layers of reinforcement

Comparison between analytical solutions and test results Obtained results to get maximum improvement benefits

References

Test Programme

• The experimental study which consists of performing a series of 25 laboratory model tests can be classified mainly as unreinforced or reinforced granular in soft sand. The tests were conducted inside a model box of (45 x 26) cm made of steel plate of 3mm thickness. The front side of the box (250 × 250) mm was made of hard glass of (10)-mm thickness to view the deformation mechanism during the test. The model surface strip footing was made of steel with dimensions (20 x 8) cm. The general test set-up is shown in Figure Pre-estimated weights of the used material(sand)

• model dimensions (box) the selected relative density of the sand, and GMM percentages

Test Results

Preliminary Tests Of Fine Sand

SPECIFIC GRAVITY OF SAND

Siev Analysis Of Sand

D10 =0.34

D30 =0.52

D60 =0.95

Cu = D60/D10 = 2.794

Cc = (d30)2/D60*D10 = 3.219

Compaction test for sand.

Plate load test for natural sand with geogrid test at 10 cm at surface:

Medium dense with geogrid at 5cm

Medium Dense With Geogrid

Comparison Of Medium Dense States

Dense state with geogrid AT 5CM

Dense With Geogrid At 5cm

Dense state 10CM

Comparison Of Dense States

Load application on natural sand

I. Reinforcement for natural sand.

II. It is found that 50% replacement of fine aggregate by M-Sand give maximum result in strength and durability aspects than the conventional concrete.

III. The results proved that the reinforcement of geogrid in natural sand induced higher compressive strength, higher split tensile strength, higher flexural strength.

IV. Since these alternative materials reduce the utility of river sand, the environmental degradation due to excessive sand mining can be minimized.

V. Thus the environmental effects, illegal extraction of sand and cost of fine aggregate can be significantly reduced.

VI. From the results it is concluded that the geogrid can be used as a reinforcement material in natural sand

References

1. J. Binquet and K. L. Lee, “Bearing capacity analysis of reinforced earth slabs,” Journal of Geotechnical Engineering Division, vol. 101, no. 12, pp. 1257–1276, 1975.

2. G. W. E. Milligan, R. J. Fannin, and D. M. Farrar, “Model and full-scale tests on granular layers reinforced with a geogrid,” in Proceedings of the 3rd International Conference on Geotextiles, vol. 1, pp. 61

66, Vienna, Austria, 1986.

3. K. H. Khing, B. M. Das, V. K. Puri, S. C. Yen, and E. E. Cook, “Foundation on strong sand underlain by weak clay with geogrid at the interface,” Geotextiles and Geomembranes, vol. 13, no. 3, pp. 199–206, 1994.

4. B. M. Das, K. H. Khing, and E. C. Shin, “Stabilization of weak clay with strong sand and geogrid at sand-clay interface,” Transportation Research Record, no. 1611, pp. 55–62, 1998

5. E. C. Shin, B. M. Das, V. K. Puri, S. C. Yen, and E. E. Cook, “Bearing capacity of strip foundation on geogrid-reinforced clay,” Geotechnical Testing Journal, vol. 17, no. 4, pp. 535–541, 1993.

6. C. R. Patra, B. M. Das, and C. Atalar, “Bearing capacity of embedded strip foundation on geogrid-reinforced sand,” Geotextiles and Geomembranes, vol. 23, no. 5, pp. 454–462, 2005.

7. B. R. Phanikumar, R. Prasad, and A. Singh, “Compressive load response of geogridreinforced fine, medium and coarse sands,” Geotextiles and Geomembranes, vol. 27, no. 3, pp. 183–186, 2009.

8. Y. L. Dong, J. Han, and X.-H. Bai, “Bearing capacities of geogrid-reinforced sand bases under static loading,” in Proceedings of GeoShanghai International Conference: Ground Improvement and Geosynthetics, pp. 275–281, June 2010.

9. V. A. Guido, D. K. Chang, and M. A. Sweeney, “Comparison of geogrid and geotextile reinforced earth slabs,” Canadian Geotechnical Journal, vol. 23, no. 4, pp. 435–440, 1986.

10.J. P. Sakti and B. M. Das, “Model tests for strip foundation on clay reinforced with geotextile layers,” Transportation Research Record, no. 1153, pp. 40–45, 1987.

11.P. K. Basudhar, S. Saha, and K. Deb, “Circular footings resting on geotextile-reinforced sand bed,” Geotextiles and Geomembranes, vol. 25, no. 6, pp. 377–384, 2007.

12.J. O. Akinmusuru and J. A. Akinbolade, “Stability of loaded footings on reinforced soil,” Journal of the Geotechnical Engineering Division, vol. 107, no. 6, pp. 819–827, 1981.

13.T. Yetimoglu, M. Inanir, and O. E. Inanir, “A study on bearing capacity of randomly distributedfiber-reinforcedsandfillsoverlying softclay,” Geotextiles andGeomembranes, vol. 23, no. 2, pp. 174–183, 2005.

14.R. J. Fragaszy and E. Lawton, “Bearing capacity of reinforced sand subgrades,” Journal of Geotechnical Engineering, vol. 110, no. 10, pp. 1500–1507, 1984.

15.. C. Shin, B. M. Das, E. S. Lee, and C. Atalar, “Bearing capacity of strip foundation on geogrid-reinforced sand,” Geotechnical and Geological Engineering, vol. 20, no. 2, pp. 169–180, 2002

16.C.-C. Huang and F. Tatsuoka, “Bearing capacity of reinforced horizontal sandy ground,” Geotextiles and Geomembranes, vol. 9, no. 1, pp. 51–82, 1990.

17.S. K. Dash, N. R. Krishnaswamy, and K. Rajagopal, “Bearing capacity of strip footings supported on geocell-reinforced sand,” Geotextiles and Geomembranes, vol. 19, no. 4, pp. 235–256, 2001.

18.S. K. Dash, S. Sireesh, and T. G. Sitharam, “Behaviour of geocell-reinforced sand beds under circular footing,” Ground Improvement, vol. 7, no. 3, pp. 111–115, 2003.

19. B. M. Das and M. T. Omar, “The effects of foundation width on model tests for the bearing capacity of sand with geogrid reinforcement,” Geotechnical and Geological Engineering, vol. 12, no. 2, pp. 133–141, 1994.

20. M. T. Adams and J. G. Collin, “Large model spread footing load tests on geosynthetic reinforced soil foundations,” Journal of Geotechnical and Geoenvironmental Engineering, vol. 123, no. 1, pp. 66–72, 1997.

21.M. T. Omar, B. M. Das, V. K. Puri, and S. C. Yen, “Ultimate bearing capacity of shallow foundations on sand with geogrid reinforcement,” Canadian Geotechnical Journal, vol. 30, no. 3, pp. 545–549, 1993.