Direct Shear Test under constant volume state for unsaturated soil

This paper examined on the shear behavior of unsaturated soil in Direct Shear Test (DST) under constant volume condition by applying the suction stress obtained from SSM (Suction stress-SWRC Method). An opening was set between the upper and the lower shear boxes before the shear process. The relationship between the shear behaviors for saturated and unsaturated soils can be explained by applying the suction stress. In addition, the principal stresses in DST were defined through applying several hypotheses, and the stress paths were analyzed with Cam clay type stress parameters. For the normalized stress plane with the equivalent stress ( p _e′), in case of saturated soil, the stress path moved along the Hvorslev surface. In case of unsaturated soil, the stress path agreed with the maximum volumetric compression line. Therefore, the suction stress has an important meaning to understand the stress path behaviors under constant volume condition.