Suction stress and its application on unsaturated direct shear test under constant volume condition

This paper examined the application of suction stress on the results of the direct shear test under constant volume condition for unsaturated soil as a subsequent study carried previously out under a constant pressure condition. In particular, the direct shear apparatus used was a modified type for unsaturated soil, and the opening between the upper and the lower shear boxes was applied with Teflon sheets. The suction stresses of each test were derived by means of the Suction stress-SWRC Method (SSM). As a result, it was found that the stress paths for unsaturated soil agreed well with the maximum volumetric compression point (M.C.P.) line, which was obtained under saturation and constant pressure conditions, through applying the suction stress in the (σnet,τ) plane. These results therefore showed that the suction stress derived from the application of the SSM can be considered to explain the mechanical behavior in saturated and unsaturated soils regardless of the two test conditions in the direct shear test.