Abstract: After Three Gorges Project completion, the reservoir water level will be raised to 175 m and lowered to 145 m every year. During the fluctuation of the reservoir water level, the quality of rock mass of the bank slopes will be deteriorated gradually in water-rock interaction of saturation-air dry cycles. Thereafter, taking sand rock at the fluctuation of reservoir water level as a representative, an experiment model the process of saturation-air dry cycles is designed. Test results show that comparing with the conventional immersion experiment, the rise or decline of water pressure and the cycle of saturation-air dry have cumulative and magnified effect on the damage of rock mass. Tests also show that the greater change of water pressure in immersion, the greater impact on the ion concentration and secondary porosity; at the same time, the more cycles of saturation-air dry, the more serious damage to the rock mass. Based on the change of ion concentration, the computational method of secondary porosity change law in the rock which is consistent with measured changes of secondary porosity is proposed. It can be applied to on-site monitoring, which can speculate the water chemical reaction in rock, and how the secondary porosity rate has developed through long-term monitoring of ion concentration. Research results lay the foundation for the study of rock mass quality of the bank slopes deteriorating in the saturation-air dry cycles.

Key words: water-rock interaction, bank slope, secondary porosity