Settlement response of soft soils reinforced by compacted sand columns

Stone/compacted sand columns is a technique of soil reinforcement that is frequently implemented in soft cohesive soils to increase the bearing capacity of the foundation soil, to reduce the settlement, and to accelerate the consolidation of the surrounding saturated soft soil. The soil-column interaction depends on several parameters, including the loading process and the loading rate, the replacement factor, the group effect, and the partial consolidation of the soft soil due to radial drainage through the column. This paper presents the results of a laboratory study that was conducted to investigate the effect of these various parameters on the settlement response of a soft foundation soil reinforced by compacted sand columns. Triaxial compression tests under different boundary conditions were performed on composite soil specimens made of annular silty soil samples with a central, compacted river-sand column. These tests, performed in a specially modified triaxial cell, show that the group effect, the replacement factor, and the consolidation of the soft soil have a significant effect on the vertical stress concentration on the column and on the settlement reduction of the foundation soil.