Failure criterion of unsaturated soil considering tensile stress under three-dimensional stress conditions

Abstract

A failure criterion on unsaturated soils has been proposed using results of triaxial tests or box shear tests under relatively high confining-stress conditions. However, mechanical behaviour of unsaturated soils under low confining stress conditions is also important because unsaturated ground exists mainly near the surface of the earth. Therefore, we examined a failure criterion for unsaturated soil under low confining stress conditions and under constant suction conditions using a hollow cylinder torsional shear apparatus. Consequently, experimental results confirmed that failure of unsaturated soil occurred promptly when the net minor principal stress, (σ3 - ua). became negative. Moreover, we proposed a failure criterion for unsaturated soil under three-dimensional stress conditions considering tensile stress. Finally, we conducted a numerical analysis introducing experimental facts to demonstrate the effects of failure criteria on slope stability problem and to discuss progressive failure of an unsaturated slope.