EFFECT OF L/B RATIO OF STONE COLUMN ON BEARING CAPACITY AND RELATIVE SETTLEMENT OF SANDY SOIL (AN EXPERIMENTAL STUDY)

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1 International INTERNATIONAL Journal of Civil Engineering JOURNAL and Technology OF CIVIL (IJCIET), ENGINEERING ISSN AND (Print), ISSN (Online), Volume 6, Issue 1, January (2), pp. -61 IAEME TECHNOLOGY (IJCIET) ISSN (Print) ISSN (Online) Volume 6, Issue 1, January (2), pp. -61 IAEME: Journal Impact Factor (214): (Calculated by GISI) IJCIET IAEME EFFECT OF L/B RATIO OF STONE COLUMN ON BEARING CAPACITY AND RELATIVE SETTLEMENT OF SANDY SOIL (AN EXPERIMENTAL STUDY) Umar Rashid Lone 1, Mohd Hanief Dar 2, Mohd Younus Ahanger 3 1 B tech, Department of Civil Engineering, NIT Srinagar, India 2 M tech, Department of Civil Engineering, NIT Srinagar, India 3 B tech, Department of Civil Engineering, NIT Srinagar, India ABSTRACT Stone columns are one method of ground improvement having a proven record of experience. They are ideally suited for improving soft clays and silts and also for loose silty sands. In spite of the wide use of stone columns and their development in construction methods, present design methods are empirical, and only limited information about designing stone columns are available in technical codes. This study is dedicated to observe practically the effect of various parameters of stone column on the bearing capacity of sandy soils by model testing. In this study square footing has been used and model tests were conducted with varying L/B ratio of stone columns. The test results followed that relative settlement was minimum corresponding to L/B ratio (of stone column) of 2.. Key Words: Stone Column, Improvement of Soft Clays and Silts, Only Empirical Results Available, Experimental Study, Best L/B Ratioobtained. 1. INTRODUCTION The stone column technique was adopted in European countries in the early 196s. Many researchers have developed theoretical solutions for estimating the bearing capacity and settlement of foundations reinforced with stone columns. Priebe, (199) proposed a method for estimating the settlement of foundations resting on an infinite grid of stone columns. The basic for this method is the unit cell concept.

2 International Journal of Civil Engineering and Technology (IJCIET), ISSN (Print), ISSN (Online), Volume 6, Issue 1, January (2), pp. -61 IAEME In spite of the wide use of stone columns and their development in construction methods, present design methods are empirical, and only limited information about designing stone columns are available in technical codes. This study is focused on the comparison of soil improvement by varying various parameters of stone columns by conducting the miniature model tests on sandy bed with a single stone column. Stone columns were installed using ramming technique. 2. MATERIAL USED (SAND) AND ITS PROPERTIES Sand was used as the primary material on which various model tests were conducted to enhance its bearing capacity by reinforcing it with stone columns. Normal aggregates of 1mm size were used as stone column material. The various properties of sand used are tabulated in table1. Property Table 1 various properties of sand Value Specific gravity 2.67 Effective grain size D1 (mm) D6 (mm) D3 (mm).2 mm.9 mm.7mm Co-efficient of Uniformity (Cc) 1.47 Co-efficient of Curvature (Cu) Minimum dry unit weight(g/cc) 1.3 Maximum dry unit weight(g/cc) 1.74 Maximum void ratio.7764 Minimum void ratio.34 Bulking of sand (max.) 3.9% of water Silt content 3.21 % Friction angle 26 Cohesion.9 kn/m 2 3. MODEL TESTS ON THE SOIL REINFORCED WITH SINGLE STONE COLUMN OF DIFFERENT L/B RATIO Model tests on the soil reinforced with single stone column (diameter 3mm) and the square plate placed in the center of the model tank with stone column exactly in the center of square plate. The sandy bed was prepared by compacting the sand in layer by layer into the steel tank of dimension ( ) cm at the % relative density. Details of proving ring, dial gauges and plate used is as under: 1 division of proving ring =.161 kg, Least count of dial gauge =.1mm Size of square plate (a) = 1cm, Area of square plate (A) =a 2 =.1 m 2 Density of sample in tank =1.638 g/cc. Weight of sand taken in tank = kg The test apparatus setup is shown in figure 1. 6

3 International Journal of Civil Engineering and Technology (IJCIET), ISSN (Print), ISSN (Online), Volume 6, Issue 1, January (2), pp. -61 IAEME Figure 1 Test apparatus setup 3.1. L/B ratio equal to. The load settlement curve for Plate Load Test (PLT) is shown in Figure 2 Load intensity (kn/m^2) Load settlement curve Figure 2 for PLT 1 Bearing capacity by double tangent method = 13.8 kn/m L/B ratio equal to 1 The load settlement curve for Plate Load Test (PLT) is shown in Figure 3. 7

4 International Journal of Civil Engineering and Technology (IJCIET), ISSN (Print), ISSN (Online), Volume 6, Issue 1, January (2), pp. -61 IAEME Load intensity (kn/m^ load settlement curve Figure 3 for PLT 2 Bearing capacity by double tangent method = 22. kn/m For L/B ratio equal to 2 The load settlement curve for Plate Load Test (PLT) is shown in Figure 4. Load intensity (kn/m^2) Figure 4 Load settlement for PLT 3 Bearing capacity by double tangent method = 238 kn/m For L/B ratio equal to 2. The load settlement curve for Plate Load Test (PLT) is shown in Figure. 8

5 International Journal of Civil Engineering and Technology (IJCIET), ISSN (Print), ISSN (Online), Volume 6, Issue 1, January (2), pp. -61 IAEME Load intensity (kn/m^2) Load settlement curve Figure Load settlement for PLT 4 Bearing capacity by double tangent method = 318 kn/m For L/B ratio equal to 3 The load settlement curve for Plate Load Test (PLT) is shown in Figure 6. Load intensity (KN/m^2) Figure 6 for PLT Bearing capacity by double tangent method = 32 kn/m RESULTS OF MODEL TESTS ON SOIL REINFORCED WITH SINGLE STONE COLUMN Model tests were conducted using square surface footing on soil reinforced with single stone column in the center of the tank with different values of L/B. 9

6 International Journal of Civil Engineering and Technology (IJCIET), ISSN (Print), ISSN (Online), Volume 6, Issue 1, January (2), pp. -61 IAEME 4.1 Comparison of bearing capacity of different model tests. The bearing capacity of various models whose test data is presented above is compared in a tabular form given in Table 2. Table 2 Comparison of bearing capacity of different model tests Test description q u of reinforced soil Footing type Stone column (L/B) (kn/m 2 ) Square(1cm) Square(1cm) Square(1cm) Square(1cm) Square(1cm) Analysis of results Comparison between relative settlements of square footing on the soil reinforced with stone column of different L/B ratio (L/B =., 1, 2, 2., 3) is presented in graphical form as shown in Figure 7.The curve shows that the soil reinforced with single stone column in the centre of L/B ratio 2. suffers a minimum settlement and its bearing capacity is more than others. On further increase of L/B ratio there is no significant increase in the bearing capacity of the soil. The effect on ultimate bearing capacity with the variation of L/B ratio is also presented in Figure 8. Relative settlement curve q/yb % settlement L/B =. L/B =1 L/B =2 L/B =2. L/B = Figure 7 Relative settlement curve soil reinforced with stone column of different L/B. 6

7 International Journal of Civil Engineering and Technology (IJCIET), ISSN (Print), ISSN (Online), Volume 6, Issue 1, January (2), pp. -61 IAEME qu (kn/m2) Effect of L/B on qu L/B Ratio Figure 8 Effect of L/B on bearing capacity. CONCLUSION From the model tests performed on the virgin soil and soil improved by the single stone column it can be concluded that relative settlement studies show that the square footing on the soil reinforced with single stone column with L/B = 2. in the center gives better bearing capacity. REFERENCES 1. Bowles, J.E. (1996). Foundation analysis and design. McGraw-Hill Book Co. 2. Rao and Ranjan, Gopal (29). Basic and Applied Soil Mechanics. New Age Publishers. 3. Munfakh, G. A. (1997). Ground improvement engineering issues and selection. 4. Elias, V., Welsh, J., Warren, J., and Lukas, R., Ground Modification Technical Summaries, Federal Highway Administration Publication No. FHWA-SA , September Humphrey, Dana, (1998) Civil Engineering Applications of Tire Shreds-Short Course for FDOT, FDEP, Gainesville, FL. 6. Ground improvement techniques by Dr.P.Purushothama Raj. 7. Ambily, A.P., and Gandhi, S.R., Behaviour of Stone Columns Based on Experimental and FEM Analysis, Journal of Geotechnical and Geoenvironmental Engineering, vol.133, 26, pp Andreou, P., Frikha, W., Canou, J., Papadopoulos, V., and Dupla, J.C., Experimental Study on Sand and Gravel columns in Clay, Ground Improvement, vol.161, 28, pp Design and construction of stone column vol. (I&II), Author R. D. Barksdale and R. C. Bachus,Feder,al Highway Administration August 198-August 1982,Office of Engineering and Highway Operations Research and Development Washington, D.C Ahmed Neamah Naji, Dr. V. C. Agarwal, Prabhat Kumar Sinha and Mohammed Fadhil Obaid, Influence of Crude Oil Fouling on Geotechnical Properties of Clayey and Sandy Soils International Journal of Civil Engineering & Technology (IJCIET), Volume, Issue 3, 214, pp. 6-7, ISSN Print: , ISSN Online: Islam M. Abo Elnaga, The Use of Urea-Formaldehyde Resin In Sandy Soil Stabilization International Journal of Civil Engineering & Technology (IJCIET), Volume, Issue 6, 214, pp. 1-9, ISSN Print: , ISSN Online: Esraa A. Mandhour, Saad N. Al-Saadi, Saad F. Ibrahim, Study of The Efficiency of Stone Columns In Soft Clay: Considering The Effect of Clay Minerals In Soil International Journal of Civil Engineering & Technology (IJCIET), Volume, Issue 9, 214, pp , ISSN Print: , ISSN Online: