Analyzing the Effect of Soil Hydraulic Conductivity Anisotropy on Slope Stability Using a Coupled Hydromechanical Framework

Hsin-Fu Yeh,Yi-Jin Tsai

doi:10.3390/w10070905

Abstract

In studies on the effect of rainfall on slope stability, soil hydraulic conductivity is usually assumed to be isotropic to simplify the analysis. In the present study, a coupled hydromechanical framework based on transient seepage analysis and slope stability analysis is used to investigate the effects of hydraulic conductivity anisotropy on rainfall infiltration and slope safety at various slope locations (the top of the slope, the slope itself and the toe of the slope). The results show that when the vertical hydraulic conductivity (Ky) is constant, the horizontal hydraulic conductivity (Kx) increases (i.e., anisotropy increases). This occurs because rainfall tends to infiltrate into the interior of the slope, resulting in the soil on top of the slope and on the slope itself being easily influenced by rainfall, leading to soil instability. The change of rainfall infiltration at the slope itself is the most significant. When the anisotropic ratio Kr (=Kx/Ky) increased from 1 to 100, the depth of the wetting zones for loam, silt and clay slopes increased by 23.3%, 33.3% and 50%, respectively. However, increased Kr led to a slower infiltration rate in the vertical direction at the toe of the slope. Compared to the results for Kr = 1 and for Kr = 100, the thickness of the wetting zones at the toe of loam and silt slopes decreased by 23.3% and 30.0%, respectively. For the clay slope, Kr changes did not significantly affect the wetting zones because of poor permeability. The results of this study suggest that the effect of soil hydraulic conductivity anisotropy should be considered when estimating slope stability to better understand the effect of rainfall on slopes.

Highlights

Studies on landslides, which occur in many parts of the world, have found that slope stability is influenced by internal factors, such as topography, geological structure of the slope and groundwater conditions and external factors, such as precipitation, earthquakes and human activity [1,2,3,4,5]
A coupled hydromechanical framework was used in this study to investigate the effects of hydraulic conductivity anisotropy on rainfall infiltration and slope safety
When the vertical hydraulic conductivity is fixed, an increase in Kr represents an increase in soil seepage mobility in the horizontal direction, making the soil on the slope itself more susceptible to rainfall infiltration, decreasing the soil safety factor

Summary

Introduction

Studies on landslides, which occur in many parts of the world, have found that slope stability is influenced by internal factors, such as topography, geological structure of the slope and groundwater conditions and external factors, such as precipitation, earthquakes and human activity [1,2,3,4,5]. Rainwater infiltrates into the pores of the soil, increasing the water content of the soil in the dry zone (above the groundwater table and near the surface), which becomes a wetting zone or transient saturated zone [10,11,12,13]. Water that infiltrates into the soil increases the shear stress and the pore water pressure of the soil. When the pore water pressure of the soil increases, the effective stress decreases, resulting in a decrease in the shear strength of the soil and a decrease in slope stability

Methods

Results

Conclusion