3D Effects of permeability and strength anisotropy on the stability of weakly cemented rock slopes subjected to rainfall infiltration

Abstract

Weakly cemented sedimentary rocks with pronounced stratification exhibit permeability and strength anisotropy. The influence of permeability and strength anisotropy on the groundwater flow and slope stability depends on the orientation of the bedding planes. The stability of slopes with different orientations of bedding planes under rainfall infiltration was evaluated in this study using three-dimensional finite element modeling. The groundwater table and pore water pressure in slopes before and after rainfall were simulated, and the calculated pore pressure corresponding to the initial and highest groundwater tables was used for slope stability analyses. The results showed that in comparison with gently dipping bedding planes, a slope with steeply dipping bedding planes exhibits a greater rise of the groundwater table and a greater increase of pore pressure, leading to a larger reduction in the factor of safety. Also, a shorter time is required to reach the highest groundwater table and the maximum pore pressure at a certain position. In consideration of the anisotropic behavior and the groundwater table rise during rainfall, unfavorable conditions were identified for the slope stability. The four unfavorable conditions, where the bedding planes and the slope face approximately strike in the same direction are: (1) the daylight condition of the bedding planes, (2) the coincidence of the bedding planes and the slope face, and (3) steep bedding planes dipping out or (4) into the slope. Slopes with the unfavorable orientations of bedding planes need additional attention in order to ensure a safe land development in the mountainous areas.