ABSTRACT
Shallow type of slope failure triggered by rainfall infiltration is common in tropical countries. The strong influence of shear strength in governing slope failure has been well established. How-ever there are still difficulties to back analyse the shallow slope failure when using conventional slope stability methods. The problem lies on the method of analysis that did not replicate the actual mechanism of failure associated with surface water infiltration and not applying the realistic soil shear strength behaviour. The soil shear strength behaviour is primarily being governed by two independent stress state variables namely net stress, (σ − ua ) and suction, (ua − uw ). The shear strength behaviour relative to these stress state variables is essentially curvi-linear and non-linear respectively. Apparently the characteristics of the shear strength behaviour at low stress levels and low suctions have a strong influence on the occurrence of the shallow rainfall-induced slope failure. This type of shear strength behaviour can be defined using the curved shear strength envelope. The main advantage of the model is that it exhibits steep drop in shear strength when the soil condition approaches saturation and when net stress approaches zero. The former is much related to the effect of infiltration in reducing the shear strength and the latter is associated with the steep reduction in strength as the depth approaches the slope surface. These aspects of strength are very much associated with the shallow infiltration triggered slope failure. This realistic curved shear strength envelope is applied in a slope stability equation. The equation is formulated in such a way that it can replicate the actual mechanism of rainfall infiltration in reducing the soil strength and increasing the soil weight. Analy-sis on cut slopes with inclination of 1:1 will be presented to demonstrate the significant of applying the curved shear strength envelope in slope failure investigation involving surface water infiltration.
