Reliability analysis of anisotropic hydraulic conductivity of shallow landslides under different rainfall pattern

Stability of the slope decreases due to the suction decreases with the rainfall infiltration. As the result, many parameters used in analysis their uncertainty will increase. In this study, reliability analysis is used for the unsaturated soil slopes. The numerical software Geo-Studio is used to simulate rainfall infiltrated inside the unsaturated soil. The analysis was performed on three typical rainfall patterns, including the advanced, normal, and delayed, with considering three different soil types (sand, silt, and clay). Anisotropic studies are defined the vertical anisotropic ratio as the ratio of vertical (k_y) to horizontal (k_x) hydraulic conductivity (k_x/k_y = 2, 10, 20). The finite element method and limit equilibrium method are used to calculate the reliability index with time. The process of infiltration into a slope due to rainfall patterns and its effect on soil slope stability is examined using numerical simulation. The reliability index of the sand unsaturated slope is 7.7 before the start of the rainfall patterns. The time for reliability index reduction becomes noticeable is early for low anisotropic ratio (k_x/k_y = 2) but during the simulate time the high anisotropic ratio (k_x/k_y = 20) has the largest reduction in the reliability index. For the silt unsaturated slope, the reliability index exist obvious reduction in the reliability index when the anisotropic ratio is low (k_x/k_y = 2). During the simulate time all the silt slope cases are sustained decreased in reliability index. Finally, effect of anisotropic conductivity for the clay slope and the reliability index, the result indicated that there is not evident different between these three anisotropic ratio.