Effect of Soaking on Shear Strength of Weathered Argillaceous Rocks Susceptible to Landsliding in the Three Gorges Area of China

Slope stability in the Three Gorges reservoir has been one of the greatest concerns for both researchers and officials in China since inundation of the Three Gorges reservoir area. Shear-strength reduction of the inundated slope materials may be one of the major causes leading to slope failures. In this study, the shear strength of three kinds of weathered argillaceous rocks that are most susceptible to landsliding was experimentally investigated after soaking the material for different periods. It was found that reduction in shear strength of all the three weathered argillaceous rocks and their strength parameters occurred significantly after soaking for about 35 days, and that a very minor reduction was observed after soaking for a longer period. The weathered argillaceous rocks with more particles coarser than silt showed a greater reduction in internal friction angle, while those with more clay and silt displayed a greater decrease in cohesion. Particle analysis of the weathered argillaceous rocks after soaking, the compositions of their clay minerals and chemical analysis of the soak water suggested that shear strength reduction of the weathered argillaceous rocks may be attributed to a combination of slaking of rock fragments coarser than silt, hydration of clay minerals, and dissolution of calcite, as well as hydrolysis of feldspar due to soaking.