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 (K y) is constant, the horizontal hydraulic conductivity (K x) 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 K r (=K x /K y) 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 K r led to a slower infiltration rate in the vertical direction at the toe of the slope. Compared to the results for K r = 1 and for K r = 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, K r 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.
In recent years, many scientific methods have been used to prove that the Earth's climate is changing. Climate change can affect rainfall patterns, which can in turn affect slope safety. Therefore, this study analyzed the effects of climate change on rainfall patterns from the perspective of rainfall intensity. This analysis was combined with numerical model analysis to examine the rainfall patterns of the Zengwen reservoir catchment area and its effects on slope stability. In this study, the Mann-Kendall test and the Theil-Sen estimator were used to analyze the rainfall records of rainfall stations at Da-Dong-Shan, Ma-To-Shan, and San-Jiao-Nan-Shan. The rainfall intensity of the Zengwen reservoir catchment area showed an increasing trend from 1990-2016. In addition, the analysis results of rainfall intensity trends were used for qualitative analysis of seepage and slope stability. The trend analysis result showed that in the future, from 2017-2100, if the amount of rainfall per hour continues to rise at about 0.1 mm per year, the amount of seepage will increase at the slope surface boundary and significantly change pore water pressure in the soil. As a result, the time of the occurrence of slope instability after the start of rainfall will decrease from 20 to 13 h, and the reduction in the safety coefficient will increase from 32 to 41%. Therefore, to decrease the effects of slope disasters on the safety of the Zengwen reservoir and its surrounding areas, changes in rainfall intensity trends should be considered for slope safety in this region. However, the results of trend analyses were weak and future research is needed using a wider range of precipitation data and detailed hydrological analysis to better predict rainfall pattern variations.
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