Effect of Stress Concentration Ratio on Shear Strength of Soft Soils Improved with Stone Columns

Numerous studies have been performed on the behavior of stone columns subjected to vertical loads. However, little research has been focused on determining the shear strength and equivalent shear strength parameters of cohesive soils reinforced with stone columns. The performed research in this area mostly includes numerical analyses which do not consider the effect of stress concentration ratio, and the value of stress concentration ratio in such analyses is assumed to be 1. In this study, an experimental investigation has been carried out on stone columns subjected to vertical and shear loads, with the purpose of determining the actual value of stress concentration ratio. The experiments were performed in a large direct shear device. In this study, single, square and triangular arrangements of stone columns with three different area replacement ratios under three vertical loads were investigated. Soft clay was used as bed material, and stone column material was either crushed stone or fine-grained sand. Results showed that stress concentration ratio decreased with the increase in stone column diameter and vertical stress and the value of stress concentration ratio is highest for square arrangement and lowest for single stone columns. The equivalent shear parameters obtained from experiments and those predicted by analytical relationships were compared at stress concentration value of 1 and stress concentration values obtained from the experiments. Results also showed that the shear strength value and the equivalent shear strength parameters measured from experiments were higher than those predicted by analytical relationships.