Infiltration type slope stability method using non-linear shear strength behaviour

Shallow slope failure in hilly area triggered by rainfall infiltration is very common in the tropics and this is very difficult to quantify using the conventional slope stability methods. Those methods assess the failure by elevating the groundwater table (GWT) and apply the Terzaghi’s linear shear strength envelope with cohesion intercept. This is despite knowing that the location of the GWT is far below to have any influence on the failure at the slope face and the true soil shear strength behaviour is perhaps non-linear at the low stress levels with zero cohesion intercept. As a result such failure cannot be pre-detected and this pose risk to the public safety if the slope is close to human activity. In order to replicate the true mechanics of failure an Infiltration Type Slope Stability Method using the non-linear failure envelope with zero cohesion intercept has been applied to assess a slope failure in Bandar Baru Selayang, Selangor, Malaysia. Consolidated Undrained Triaxial tests have been conducted on undisturbed soil specimens to substantiate that the failure envelope is perhaps non-linear at low stress range and has zero cohesion intercept. The slope stability analyses back calculate the failure by considering various depths of infiltration. This approach managed to prove that the factor of safety (FOS) is less than unity when the wetting front reached the depth of the actual slip failure surface.