Direct Shear Testing on Unsaturated Silty Soils to Investigate the Effects of Drying and Wetting on Shear Strength Parameters at Low Suction

Abstract

A modified conventional direct shear device was used to measure unsaturated shear strength of two silty soils at low suction values (∼0–50 kPa) that were achieved by following drying and wetting paths of soil-water characteristic curves (SWCCs). The results revealed that the internal friction angle of the soils was not significantly affected by either the suction or the drying-wetting SWCCs. The apparent cohesion of soil increased with a decreasing rate as suction increased. Shear stress–shear displacement curves obtained from soil specimens subjected to the same net normal stress and different suction values showed a higher initial stiffness and a greater peak stress as suction increased. A soil in wetting exhibited slightly higher peak shear stress and more contractive volume change behavior than that of soil in drying at the same net normal stress and suction.