Abstract: The bank slope of the reservoir is inevitably affected by the excavation unloading during the project construction. In this study, we selected sandstone from the typical bank slope in Three Gorges Reservoir Region. Water-rock cycle experiments were carried out to simulate the variation of water levels and immersion-air drying cycles. Especially, the water-rock interaction effect on unloading mechanical properties and microstructure of stratification sandstone was mainly analyzed. The results showed that in the course of ten times of water-rock cycles, the triaxial unloading and shear strength of sandstone presented initially a steep deterioration and later gradual deterioration trend. The first four times accounted for about 70% in the overall deteriorating degree, which indicated the degree in the last three cycles slowed down. As the water-rock cycle times increased, the deformation modulus of rock specimen decreased gradually before uploading at the same confining pressure. During the unloading process of confining pressure, the linear graded phase of deformation modulus gradually became shorter, whereas the nonlinear mutation phase became longer and slower. The brittle feature of rock specimen slowly weakened, whereas its plasticity enhanced. The repeated fluctuations in water pressure and the immersion-air drying cycle resulted in an irreversible slow and accumulated damage to the rock specimen. Microscopically, micro-cracks, cracks and pores of rock steadily developed and accumulated. Macroscopically, the porosity rate increased, and the triaxial unloading and shear strength decreased. This study can provide references for the analysis of excavation, unloading and deformation of slope rock mass in bank slopes.

Key words: bank slope, water-rock interaction, unloading, deteriorating rule, microstructure