Deformation behavior of sandy slopes during rainwater infiltration

Rainfall-induced slope failures often occur within a short period of time during or immediately after heavy rainfall. To analyze the mechanism and conditions leading to such failures, constant shear stress drained triaxial tests, which mimic the field stress path, were conducted on three sets of sandy samples obtained from sites of previous disastrous landslides. The effects of various parameters, such as initial relative density and principal stress ratio, on the temporal development of deformation were examined. Behavior after initiation of failure was significantly affected by the mode of deformation, i.e., whether compressive or dilative. Compressive soil failed rapidly due to increased pore-water pressure associated with the shearing process, while dilative soil exhibited slow failure due to loss in pore-water pressure during dilation that increased the shearing resistance of soil. Moreover, conventional triaxial drained and undrained tests were also performed to illustrate the difference in soil response under different stress paths. The results demonstrated that in analyzing the stability of slopes under rainwater infiltration, the use of strength parameters associated with failure initiation in constant shear stress drained tests may be more appropriate than those obtained from conventional triaxial tests.