Experimental Study on Shear Strength of Cohesive Soils Reinforced with Stone Columns

Stone columns are mostly designed to carry compressive loads. However, in some cases, the movement of soil mass can result in lateral deformations, and consequently shear stresses in soil and stone column. The study presented herein is an experimental program, aimed to investigate the shear strength of soft clay bed reinforced with stone column. Modeling of undrained, short-term behavior of clay bed reinforced with stone column was performed using a large direct shear testing device with in-plane dimensions of 305 × 305 mm. In this study, the effect of key parameters including area replacement ratio, stone column arrangement, normal pressures value, and stone column material was experimentally evaluated. For this purpose, three different replacement ratios, stone column arrangements (single, square and triangular) and normal pressures (35, 55 and 75 kPa) and two different materials including crushed gravel and fine-grained sand were used in experiments. Results showed that in the presence of stone column, the shear strength and the overall stiffness of soft clay bed increased. The stone column arrangement, area replacement ratio and stone column material were also shown to have an impact on improving the shear strength. The most and the least increase in shear strength and stiffness values were related to square arrangement of columns and single column, respectively. In this study, the variation of stress concentration ratio of stone columns under shear loads were measured using suitable instruments. Also, the equivalent shear strength and equivalent shear parameters measured from experiments were compared with those predicted by analytical relationships at stress concentration value of 1 and stress concentration value obtained from experiments.