Multiscale Study of the Deterioration of Sandstone in the Three Gorges Reservoir Area Subjected to Cyclic Wetting–Cooling and Drying–Heating

Seasonal changes in the reservoir water level (RWL) and groundwater level can lead to cyclic actions of wetting–drying and accelerate the weathering process of rocks within the hydrofluctuation belt in the reservoir region, which over many years would eventually result in many geological disasters, such as landslides and rock mass collapse. The cyclic wetting–cooling and heating–drying process, exerted on the rock mass within the hydrofluctuation belt in the TGR area, is a combination of wetting–drying cycles and cooling–heating cycles, however, these processes have not been clearly identified and quantified. In this paper, a multiscale study is conducted to investigate the physical and mechanical features of sandstone samples in the Three Gorges Reservoir (TGR) region subjected to 20 wetting–cooling and drying–heating cycles under temperature changes of 0 °C, 30 °C, 60 °C, and 100 °C. Then the deterioration mechanism of the rock masses within the hydrofluctuation belt in the TGR area is discussed. The results show that the multiscale physical properties, including mineral compositions, microstructures, pore size distribution characteristics, permeability and macromechanical parameters, are markedly altered during the cyclic wetting–cooling and drying–heating process. The two physical processes (cyclic wetting–drying and cyclic cooling–heating) are both found to deteriorate the sandstone samples in the experiment, and the coupled action of the two processes can accelerate the deterioration rate of the sandstone samples. The deterioration rates of the multiscale physical and mechanical properties of the sandstone samples under larger temperature changes are higher. Furthermore, rock masses at different depths are subjected to cyclic wetting–cooling and drying–heating with different temperature changes, which is an important reason for the stratification of the deterioration zone in the hydrofluctuation belt in the TGR area. Highlights The rock masses within the hydro-fluctuation belt in the reservoir bank are actually subjected to the combined action of cyclic wetting–drying and cooling–heating. The two physical processes (cyclic wetting–drying and cyclic cooling–heating) both are found to deteriorate the sandstone experimentally. The coupled action of the cyclic wetting–drying and cooling–heating can accelerate the deterioration rate of the sandstone. Rock masses at different depths are subjected to different temperature changes, which is an important reas