Effect of Sand Columns on the Load Response of Soft Clays

Stone or sand columns in soft clays have been used to increase the load carrying capacity, reduce the settlement, and decrease the generation of excess pore water pressure during loading. The main objective of this paper is to investigate the effect of sand columns on the undrained shear strength of soft clayey material. For this purpose, consolidated undrained triaxial tests were performed on normally consolidated Kaolin specimens that were reinforced with sand columns and tested at confining pressures of 100, 150, and 200 kPa. The parameters that were varied are the diameter of the sand columns, the height of the column, and the confining pressure. Results indicate substantial improvements in undrained shear strength reaching 75% for a maximum area ratio (ratio of area of sand column to area of specimen) of 17.8%. The data collected supports the hypothesis of a "critical column length" that is greater than about six column diameters, beyond which the increase in undrained shear strength due to the presence of the sand columns becomes negligible. Finally, the data did not show any clear indication of the effect of the confining pressure on the improvement in the undrained shear strength of the "reinforced" clay specimen.