The effect of soil type on matric suction and stability of unsaturated slope under uniform rainfall

It is well understood that rainfall infiltration decreases the unsaturated shear strength of soil slope due to reduction in matric suction as the wetting front moves through it. However, how much the matric suction is reduced that may affect slope stability results is still unknown. The paper presents the numerical results of wetting front depth, matric suction and stability results in term of reliability index for a single rainfall intensity. The analyses are for five soils using the modified Mohr-Coulomb failure criterion in conjunction with a finite element saturated-unsaturated seepage model. The numerical results show that the matric suction results are differently affected for soils with rainfall infiltration. The change in reliability index result is insignificant as long the soil remains unsaturated as the wetting front moves. The reliability index results are however become noticeable if the infiltrated rainfall produces saturation and positive pore-water pressure. The difference in results may be attributed to the wetting front depth and its saturation that depends on saturated-unsaturated hydraulic conductivity and matric suction head.