Mechanical behavior of granite residual soil during wetting considering effects of initial unloading

The unloading caused by slope excavation may affect soil behavior during the subsequent rainfall-induced wetting. However, the previous wetting tests do not greatly consider this fact. For this reason, the unloading-wetting tests are carried out on granite residual soil, and the effects of consolidation pressure and stress ratio (reflecting the degree of the initial unloading) are investigated. The influences whether excavation takes place before or after rainfall are studied. It is found that the granite residual soil shows notable anisotropy during wetting, and the horizontal deformation is greater than the vertical one when wetted under isotropic stress condition. The overall level of wetting deformation increases with the increase of consolidation pressure. As the degree of the initial unloading increases, the wetting-induced axial and shear strains increase, the wetting-induced dilatancy becomes stronger, and the initially compressive lateral wetting deformation changes into extensional somewhere. Whether excavation takes place before or after rainfall makes a difference to the deformation behavior of soil. The soil specimen in the unloading-wetting tests shows larger axial and shear strains but smaller lateral and volumetric strains, compared with that in the wetting-unloading tests. The increasing degree of the initial unloading causes the strength properties, mainly cohesion, of wetted soil to decrease.