Evaluation of shear strength parameters for rain-induced slope instabilities

摘要

The stress path followed by a soil element along a potential failure plane in a slope subjected to rainfall infiltration is characterized by pore pressure increase at almost constant total stress condition. This stress path can be simulated in the laboratory by conducting constant shear stress drained (CSD) triaxial tests wherein back pressure within a saturated soil specimen is increased while keeping the shear stress constant, i.e. σ_1 and σ_3 are kept constant. Such stress path is obviously different from that reproduced in conventional triaxial tests in which σ_3 remains constant and σ_1 increases. To investigate the soil response under different stress paths, CSD tests, as well as conventional triaxial drained and undrained tests, were performed on sandy soils obtained at previous landslide sites. The test results confirmed that CSD-derived strength parameters were more appropriate when analyzing rainfall-induced failure initiation. Realizing that CSD tests are not easy to perform, correlations were made to express the strength parameters obtained through conventional triaxial tests with those derived from CSD tests.