Damage evolution of dynamic characteristics of sandstone under the sequential action of water-rock interaction and cyclic loading and unloading

The rock mass in the hydro-fluctuation belt of the reservoir bank slope is subjected to long-term water-rock interaction and frequent moderate-low intensity reservoir earthquake. The deterioration of the mechanical properties of the rock mass caused by this directly affects the dynamic response and seismic capacity of the reservoir bank slope. Based on this, the settings of the fluctuating zone of the bank slope of the reservoir are simulated, and the water-rock interaction test to simulate the periodic rise and fall of the reservoir water level is designed and carried out. In the course of the test, the cyclic loading and unloading method is used to simulate the influence of seismic action, and the sequential action of water-rock interaction and cyclic loading and unloading is mainly considered. According to the test results, the following conclusions are obtained. (1) The dynamic parameters of the rock sample generally change exponentially from steep to gentle under the water-rock interaction. After considering the sequential action of water-rock interaction and cyclic loading and unloading, the deterioration rate and trend of dynamic parameters of rock samples increase obviously, indicating that frequent moderate-low intensity reservoir earthquakes can obviously promote the damage development of bank slope rock mass in the environment of water-rock interaction for a long time. (2) Under the action of water-rock interaction and cyclic loading and unloading, the microstructure of rock samples gradually loosens from the compacted state, and the corresponding integrity degradation coefficient and the secondary porosity also show a trend of steepness and then slowness. Among them, the microstructure changes of rock samples under the sequential action of periodic water-rock interaction and cyclic loading and unloading are the most significant, followed by the rock samples with initial cyclic loading and unloading damage, and the change of rock samples under the water-rock interaction alone is the smallest. The changes and differences of the microscopic structure of the rock sample under different schemes also govern the degradation law of its dynamic characteristics. (3) Under the long-term water-rock interaction and frequent moderate-low intensity reservoir earthquakes, the internal damage of the reservoir bank slope will gradually accumulate and develop, which will directly affect the dynamic response characteristics and seismic capacity of the reservoir bank slope. Therefore, the degradation law of the dynamic characteristics of the bank slope rock mass should be systematically considered in the analysis and evaluation of long-term seismic performance of reservoir bank slope.