Effects of Soil–Water Interaction on the Mechanical Behaviors of Shear-Zone Soils

This paper reports the effects of soil–water interaction on the mechanical behaviors of shear-zone soils taken from a bedding landslide in the Three Gorges Reservoir area of China. Two types of wetting treatment, namely cyclic wetting–drying and soaking in fluid, are adopted to mimic the enduring effect on landslide materials caused by reservoir operation. The effect induced by rainfall infiltration is also mimicked by varying water contents in the soils. The degree of soil–water interaction is indicated by the shear strength obtained from reversal direct shear and ring-shear tests. The experimental results indicate that the enduring soil–water interaction gives rise to significant disintegration of the soil particles, whereas the increasing water content greatly decreases the friction between particles at the shear surface. All this interplay between water and shear-zone soils leads to dramatic reduction in the shear strength. Moreover, it is found that the friction angle is more sensitive to cyclic wetting–drying pretreatment, while soaking pretreatment has a larger influence on the stiffness and cohesion of the soils.