Stability Analysis of Soil Slope Subjected to Perched Water Condition

Abstract

Perched water zone occurs in the subsurface of the slope under heavy rainfall or above an impeding layer with relatively low permeability. It causes a decrease in the shear strength of the soil and the increase in the loading on the slope. As the most used method of estimate the slope stability, the limit equilibrium method considers the influence of rainfall infiltration on the slope stability by increasing the underground water table and decreasing the shear strength parameters on the slip surface. However, the contribution of perched pore water pressure is usually ignored. To incorporate the effect of perched water pressure into the stability analysis, the Bishop's simplified method and Janbu's simplified method are modified to perform stability analysis in the situation of circular and composite slip surfaces, respectively. The detailed methodology and numerical implement procedure are presented. Then, three examples are adopted to verify the proposed methods and to investigate the impact of the perched water zone on slope stability. The results show that the program developed in this study has considerable accuracy compared to commercial software. The pore water pressure in the perched water zone has important impacts on slope stability, especially when the depth of the perched water zone is greater than 4 m. Ignoring the perched pore water pressure in the slope stability analysis might overestimate the safety status of the slope.