Instability of Unsaturated Soils Under Constant Deviatoric Stress in Drained Conditions

The paper presents the results of an experimental investigation to study the instability of unsaturated slopes under constant deviatoric stress in drained conditions. The experimental program included compression triaxial tests on specimens prepared with various degree of compactions, i.e., 68%, 76%, and 83% and subjected to net confining stresses of 30, 50 and 90 kPa. During shear process, the specimens were first sheared in constant water content conditions to the pre-defined value of deviatoric stress (i.e., 25% of qmax). The pre-defined deviatoric stress on specimens was then kept constant, and matric suction was decreased by increasing pore water pressure to start water infiltration. After completed water infiltration, the specimens were sheared again in constant water content conditions. The results showed that the behavior of soil is affected significantly by variation in the degree of compaction and confining stress when subjected to water infiltration. Very loose soil with low net confining stress showed large collapse deformation. Finally, it was also observed that the gradient of the failure line is increased from 1.08 to 1.32 with an increase in the degree of compaction, hence increasing the stability of slopes.