IGC. 50 th INDIAN GEOTECHNICAL CONFERENCE BEHAVIOUR OF GEOTEXTILE ENCASED QUARRY WASTE COLUMN SUBJECTED TO SHEAR LOADING IN SOFT CLAY

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1 th th INDIAN GEOTECHNICAL CONFERENCE 17 th 19 th DECEMBER, Pune, Maharashtra, India Venue: College of Engineering (Estd. 184), Pune, India BEHAVIOUR OF GEOTEXTILE ENCASED QUARRY WASTE COLUMN SUBJECTED TO SHEAR LOADING IN SOFT CLAY P. Lakshmi Divakaran 1,Post Graduate Student, IES College of Engineering, Thrissur, Remya Sasidharan 2, Assistant Professor, IES College of Engineering, Thrissur, ABSTRACT Stone column is a ground improvement technique that can be used for supporting structures such as buildings, embankments etc in soft soils. The axial load capacity of the stone columns is mainly derived due to the confinement of the surrounding soil. When the stone columns are installed in soft clays, the confinement may not be adequate. Thus its load capacity cannot be derived properly due to poor confinement of the surrounding clay. It is seen from the literatures that when the stone columns are wrapped with a geosynthetic, its load carrying capacity has been improved. The load carrying capacity of the stone column also depends upon the fill material. The use of stones is proved to be better as the column fill material. Quarry waste is a cheap and easily available waste material. The effectiveness of using the quarry waste as the column fill material need to be studied. Stone columns can be used below embankments, retaining walls etc. They are generally designed such as to carry the vertical loads. But in the field there is a chance of soil movements leading to lateral movement of the soil. This may cause shear deformation in the stone column. With the development of these lateral flows of the soil, there may cause lateral translation of the stone column. If proper confinement is provided to stone columns, the problem of shear movement of the soil can be prevented. The paper describes the behaviour of quarry waste column when it is encased with and without geotextile while subjected to shear loading. For this a laboratory model study was conducted. The model test was conducted in a test tank of size 7mm x 3 mm and 3mm height according to unit- cell idealization. Load tests were conducted in a group of two mm diameter quarry waste column. The shear loads are produced on the quarry waste column by loading on the area adjacent to the quarry waste column. Quarry dust is used as the column fill material. To study the effect of type of geosynthetic encasement, two different types of geotextiles, woven geotextile and non woven geotextile having different tensile strengths were used. There are so many design parameters that may affect the stone column construction, of which spacing is an important parameter. Thus shear loads were generated under different spacings of, 2.D and. The results have shown that the shear stiffness of the quarry waste column have increased when it is being encased with geotextile. The shear load capacity of the soft clay has increased with the inclusion of quarry waste column and there is further improvement in the shear load capacity when encased with the two types of geotextiles. Though the use of geotextile encasement has shown improvement in its performance, the difference in the improvement achieved between the woven and nonwoven geotextiles is negligible. Also it was found that the spacing of the quarry waste column have

2 P. Lakshmi Divakaran, & Remya Sasidharan significant effect in the shear load capacity of the soft clay. As the spacing increases, the shear load capacity is found to be decreasing. It was noticed that the optimum spacing of the quarry waste column is 2.D. Keywords: Non woven Geotextile, Quarry waste column, Spacing, Woven Geotextile 1 Behaviour of geotextile encased quarry waste column subjected to shear loading in soft clay_p. Lakshmi Divakaran1, Department of Civil Engineering, IES College of Engineeering, Thrissur, India, lakshmidivakaran3@gmail.com 2 Behaviour of geotextile encased quarry waste column subjected to shear loading in soft clay _Remya Sasidharan2, Department of Civil Engineering, IES College of Engineeering, Thrissur, India, remyasandeep@ymail.com

3 th th INDIAN GEOTECHNICAL CONFERENCE 17 th 19 th DECEMBER, Pune, Maharashtra, India Venue: College of Engineering (Estd. 184), Pune, India BEHAVIOUR OF GEOTEXTILE ENCASED QUARRY WASTE COLUMN SUBJECTED TO SHEAR LOADING IN SOFT CLAY P. Lakshmi Divakaran. 1, Post Graduate Student, IES College of Engineering, Remya Sasidharan. 2, Assistant Professor, IES College of Engineering, ABSTRACT: While using stone column in the field the soil movements may lead to lateral movement of soil. This may cause shear deformation and lateral translation of stone column. This paper describes the behaviour of quarry waste column encased with and without geotextile subjected to shear loading under spacings of, 2.D and. Results have shown that shear stiffness of quarry waste column and shear load capacity of soft clay have increased when encased with geotextile. As the spacing increases, the shear load capacity is decreasing. It was noticed that the optimum spacing of the quarry waste column is 2.D INTRODUCTION Stone column is a common ground improvement technique for the construction of embankments on soft clay soils. The stone columns are usually designed for carrying vertical loads from the structures. However, in the case of soft foundation soils, lateral flow of soil may occur, leading to lateral thrust on the stone columns. One common example where the stone columns may be subjected to such lateral soil movement is the case at the toe of embankments (Fig 1). Such a soil movement will exert severe lateral pressure on the stone columns. Another case could be due to lateral soil movements during earthquake induced ground motions. The pressure from the surrounding soil may cause shear failure in the stone column when the confinement from the soil is not adequate. Consequently, the stone column may undergo lateral translation. While encasing the stone column using geosynthetic, it may impart the necessary confinement to improve their lateral stiffness. Thus in the present study, the effect of the geotextile encased stone column when subjected to shear loading at different spacing is also examined. Fig. 1 Lateral thrust on stone columns at the toe of an embankment The pressure from the surrounding soil may cause shear failure in the stone column when the confinement from the soil is not adequate. Consequently, the stone column may undergo lateral translation. When the stone columns are encased with suitable geosynthetic, it may impart necessary confinement to the stone column and can improve their lateral stiffness. As the stone aggregates are confined, they can mobilise higher

4 P. Lakshmi Divakaran, & Remya Sasidharan shear strength and the resistance against lateral soil movement can be improved significantly. EXPERIMENTAL STUDY Materials Used Soil used for the study was disturbed sample and was collected from a paddy field at Puranattukara, Thrissur at a depth of 1m from the ground level. The soil was initially air dried in open atmosphere prior to the testing. The soil was sieved through 4.7mm sieve to remove the coarser fraction. The soil passing through 4.7mm sieve was used for the entire study. The properties were determined and are listed in Table 1. Table 1 Properties of soil Properties Specific gravity Liquid limit(%) Plastic limit(%) Plasticity index(%) Shrinkage limit(%) Clay(%) Silt(%) Sand(%) Maximum dry density(g/cc) Optimum moisture content(%) Values Quarry waste was collected from Thomson Granite Quarry situated at Mulayam, Thrissur. Quarry waste which passes through 4.7 mm and retained on 4 micron sieve was used as the column fill material. The properties of the geotextiles were listed in Table 2. Table 2 Properties of Geotextiles Parameter Maximum density, ϒ d max (kn/m 3 ) Minimum density, ϒ d min (kn/m 3 ) Angle of internal friction, Values Woven and Nonwoven geotextile were used for the study. TF1 3 and PR were the two types of geotextiles used for encasing the quarry waste column. TF1 3 is a woven geotextile, manufactured from high tenacity, high molecular weight multifilament Polyester yarn. PR is a needle punched nonwoven geotextile. The properties of the geotextiles were listed in Table 3. Table 3 Properties of woven and nonwoven geotextiles Properties TF1 PR 3 Tensile strength MD (kn / m) 9 Tensile strength CD (kn / m) Elongation MD/CD (%) ±2 ±2 Tensile 8 _ (MD) (kn / m) PHYSICAL MODELLING A rectangular tank of 7mm length, 3mm width and 3mm height was used for the experiment. Three PVC pipes of mm diameter were used for making the column. The test were conducted by varying the spacing of the quarry waste columns. Loading plate used for the two loading tests were having a dimension of 3mm x 3mm. The size of the test tank and the loading plate was selected based on the unit cell concept. The parameters varying in the shear loading tests were spacing between columns and tensile strength of geotextile. The quarry waste columns were formed by placing two columns parallel to the loading plate. Preparation of Soft Soil Bed To make the soil into a soft consistency, the soil was first mixed with water equal to liquid limit. This forms slurry that was free from any lumps. This slurry was placed in buckets of equal dimensions with proper drainage at both ends. For this, sufficient holes were provided at the bottom of each bucket and then it was filled with 6 mm sized stones upto a depth of mm. Over this a filter paper was provided so as to avoid the mixing of the stone and slurry. Also the slurry does not block the drainage path. Over the slurry, another sheet of filter paper was provided and a thermocol disc was placed above it. Dead weights were provided above it using mm x mm concrete blocks of 9 kg weight to allow consolidation. Consolidation of clay bed was continued for a period of 2 days until the water content reduced to a soft consistency. By this method, clay beds of uniform moisture content and consistency were obtained throughout the test. Fig 4.6 shows the

5 th th INDIAN GEOTECHNICAL CONFERENCE 17 th 19 th DECEMBER, Pune, Maharashtra, India Venue: College of Engineering (Estd. 184), Pune, India consolidation of soil sample. Before filling the test tank with the prepared clay, inner surface of the tank was smeared using oil in order to avoid side wall friction. The soil was filled upto a depth of 3mm in the test tank for the two loading tests. Formation of Quarry Waste Column Inorder to construct the quarry waste column a PVC pipe having an outer diameter equal to the diameter of the column was used. The quarry waste column were arranged in a triangular pattern for axial loading test, three PVC pipe of mm diameter was placed at spacing of 2 times diameter of column, 2. times diameter of column and 3 times diameter of column at the centre of the tank. The quarry waste columns were installed by displacement method, and were extended down to the bottom of the tank. For encased quarry waste columns, the PVC pipes were encased with geotextiles. The quarry waste columns were extended to the full depth of the soil placed in the tank for a height of 3 mm so that l /d ratio (length of the column/diameter of the column) is a minimum of 6, which is required to develop the full limiting axial stress on the column. Around this pipe, clay bed was formed. The clay layer was molded gently by hand to expel air during the process of filling. PVC pipe was then removed from the bed without causing any disturbance to the clay bed. The quantity of the quarry waste required to form the column was premeasured and charged in to the casing pipe in three layers. Quarry waste was carefully charged into the hole in layers. Each layer was compacted using 12 mm diameter rod to achieve a density of 1.97 g/cc, so that ϕ = 4 corresponding to a relative density of 7%. After charging the first layer of the hole with quarry waste, the PVC pipe was gently lifted up so as to leave the encasement intact in the case of encased quarry waste column. Thus the intrusion of surrounding clay into the quarry waste column or neck formation in the geosynthetic in the case of encased quarry waste column due to the lateral thrust of the surrounding clay can be prevented (Murugesan and Rajagopal ). Shear Loading Test The shear loading test was done by placing two quarry waste columns parallel to the loading plate, at spacing of, 2.D and with and without geotextile encasement at a clear distance of mm from the loading plate. The clay bed was then subjected to strain controlled compression loading in universal testing machine at a strain rate of 1. mm / min. Test was conducted up to a maximum settlement of mm for shear loading tests. Figure 2 shows the test specimen for the shear load test. Fig. 2 Test setup for shear loading RESULTS AND DISCUSSIONS Shear Resistance of Soil Loading was done at a clear gap of mm from the quarry waste columns at different spacings with and without geotextile encasement. Figure 3 shows the pressure- settlement response of clay with quarry waste column placed at spacing of, 2.D and with a clear gap of mm from the loading plate.

6 Settlement (mm) Settlement (mm) Settlement (mm) P. Lakshmi Divakaran, & Remya Sasidharan 3 Fig. 3 Pressure- settlement response of clay with quarry waste column Figure 4 shows the pressure- settlement response of clay with nonwoven geotextile encased quarry waste column placed at spacing of, 2.D and with a clear gap of mm from the loading plate clay Fig. 4 Pressure- settlement response of clay with nonwoven geotextile encased quarry waste column with different spacing Figure shows the pressure- settlement response of clay with woven geotextile encased quarry waste column placed at, 2.D and with a clear gap of mm from the loading plate. 2.D 2.D 3 3 Fig. Pressure- settlement response of clay with woven geotextile encased quarry waste column at different spacing Figure 3, Figure 4 and Figure shows that the bearing pressure of the soil has improved when the quarry waste column was encased with nonwoven geotextile while subjected to shear loading at a clear gap of mm. The bearing pressure of the soil decreases with increase in the spacing between the columns from to. But there is only slight variation in the bearing pressure of the soil when the columns are placed at and 2.D. The bearing pressure of the soil has further decreased when the spacing between the columns increases from 2.D to. Thus 2.D is the optimum spacing of the columns when subjected to shear loading. The variation in the bearing pressure of the soil subjected to shear loading can be attributed to the shear resistance of the soil. It has shown that the shear resistance of the soil increases with the inclusion of the quarry waste column. With increase in the spacing of the column, the shear resistance of the soil was found to be decreasing. As the spacing increases from to 2.D, the shear resistance of the soil has been decreased and it further decreases when the spacing has increased from 2.D to. Figure 6 shows the pressure- settlement response of clay with and without geotextile encased quarry waste column placed at optimum spacing with a clear gap of mm from the loading plate. 2.D

7 th Lateral deflection (mm) Lateral deflection (mm) Settlement (mm) th INDIAN GEOTECHNICAL CONFERENCE 17 th 19 th DECEMBER, Pune, Maharashtra, India Venue: College of Engineering (Estd. 184), Pune, India 3 3 QC NE QC WE QC Fig. 6 Pressure- settlement response of clay with and without geotextile encased quarry waste column at optimum spacing It can be observed from Fig. 6 that inclusion of quarry waste column increases the bearing pressure of the soil subjected to shear loading at optimum spacing. The bearing pressure has improved further when it is being encased with a geotextile. The bearing pressure improvement is significant while encasing the quarry waste column with the woven and nonwoven geotextiles. But the improvement in the bearing pressure achieved between woven and nonwoven encased quarry waste columns is negligible. This have shown that the tensile strength of geotextile have less effect in the bearing pressure of soil subjected to shear loading. The bearing pressure of the soil can be expressed as the shear resistance of the soil. Thus the shear resistance of the soil has improved with the inclusion of quarry waste column and it has improved further while being encased with a geotextile. The tensile strength of the geotextile has negligible effect on the shear resistance of the soil. This has proved that the quarry waste columns require only an encasement to provide a resistance to bulging of column. Lateral Deflection of the Quarry Waste Column While applying shear loading to the column, the top end of the column may deflect laterally. The lateral deflection of the quarry waste column depends on the extent to which it resists lateral deformation in response to an applied force. This means that the lateral deflection of the quarry waste column depends on the lateral stiffness of the column. The lateral deflection at the top end of the quarry waste column when subjected to shear loading was measured using the dial gauges at the top of the columns. Figure 7 shows the pressure vs lateral deflection at the top end of quarry waste column placed at spacing of, 2.D and with a clear gap of mm from the loading plate. 3 3 Fig. 7 Pressure vs lateral deflection at the top end of quarry waste column Figure 8 shows the pressure vs lateral deflection at the top end of the Nonwoven encased quarry waste column placed at, 2.D and with a clear gap of mm from the loading plate. 3 4 Fig. 8 Pressure vs lateral deflection at the top end of the Nonwoven encased quarry waste column 2.D 2.D

8 Lateral deflection (mm) Lateral deflection (mm) P. Lakshmi Divakaran, & Remya Sasidharan Figure 9 shows the pressure vs lateral deflection at the top end of the Woven geotextile encased quarry waste column placed at a clear gap of mm from the loading plate. 3 4 Fig. 9 Pressure vs lateral deflection at the top end of the Woven geotextile encased quarry waste column It can be observed from Fig.7, Fig. 8 and Fig. 9 that the lateral stiffness of the woven encased quarry waste column decreases with increase in the spacing between the columns from to when subjected to shear loading with mm clear gap. The lateral stiffness of the column will be higher when the columns are placed at. The lateral stiffness decreases when the spacing of the columns further increases from 2.D to. Fig. shows the pressure vs lateral deflection at the top end of the quarry waste column with and without geotextile encasement at optimum spacing with a clear gap of mm from the loading plate. 3 4 QC Fig. Pressure vs lateral deflection at the top end of the quarry waste column with and without geotextile encasement at optimum spacing It can be observed from the Fig. 9 that the lateral stiffness of the column increases while it is being encased with a geotextile when subjected to shear 2.D NEQC WEQC loading at a clear gap of mm. The lateral stiffness of the column is increased when encased with woven and nonwoven type of geotextile. The lateral stiffness is almost same for woven geotextile encased quarry waste column and nonwoven geotextile encased quarry waste column. This has shown that the tensile strength of the geotextile has no significant effect in the lateral stiffness of the column. CONCLUSION Shear resistance of the soil has improved with the use of quarry waste column. The shear resistance has increased with the decrease in the spacing between the columns. Optimum spacing of quarry waste column is about 2. times that of the diameter of the quarry waste column. Shear resistance of the soil has improved by 42% with the installation of quarry waste columns. The shear resistance of the soil has increased when the columns are encased with geotextile. Geotextile encased quarry waste column shows better shear resistance than unreinforced quarry waste column. Woven and nonwoven geotextile encased quarry waste column has shown similar shear resistance. The shear resistance of the soil has shown 7 to 77% increase with the use of nonwoven and woven geotextile encased quarry waste columns. There is 31% improvement in the lateral stiffness of the column when it is being encased with woven and nonwoven geotextile. In general quarry waste columns encased with geotextile can be used as an economic and efficient method for improving the soft soil. The geotextile encased columns can prevent shear failure of the columns. Thus geotextile encased quarry waste columns can be used to be provided safely without any shear failure at the bottom of the embankments.

9 th th INDIAN GEOTECHNICAL CONFERENCE 17 th 19 th DECEMBER, Pune, Maharashtra, India Venue: College of Engineering (Estd. 184), Pune, India REFERENCES 1. Balan, K., Jayasree, P. K., and Thushara, T. S. (13). Studies on natural geotextile reinforced quarry waste columns for soft soil stabilization. Proceedings of Indian Geotechnical Conference December, Roorkee, pp Rakesh, K., and Jain, P. K. (13). Soft ground improvement with fiber reinforced granular pile. International Journal of Advanced Engineering Research and Studies, 2(3), pp Tandel Y.K., Solanki C. H., and Desai A. K. (12). Reinforced stone column: remedial of ordinary stone column. International Journal of Advances in Engineering and Technology, 3(2), pp Murugesan, S., and Rajagopal, K. (). Studies on the behaviour of single and group of geosynthetic encased stone columns. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 136(1), pp Gniel, J., and Bouazza, A. (9). Improvement of soft soils using geogrid encased stone columns. Geotextiles and Geomembranes, 27, pp Issac, D. S., and Girish, M. S. (9). Suitability of different materials for stone column construction. Electronic Journal of Geotechnical Engineering, 14, pp Ambily, A. P., and Gandhi, R. S. (7). Behaviour of stone columns based on experimental and fem analysis. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 133(4), pp Malarvizhi, S. N., and Ilamparuthi, K. (7). Comparative study on the behaviour of encased stone column and conventional stone column. Japanese Geotechnical Society, 47(), pp Sharma, R. S., Phani Kumar, B. R., and Nagendra, G. (4). Compressive load response of granular piles reinforced with geogrids. Canadian Geotechnical Journal, 41, pp Indian Standards (IS). (3). Indian standard code of practice for design and construction for ground improvementguidelines. Part 1: Stone columns. IS 284 (Part 1), New Delhi, India.