Field test study on rock mass deterioration characteristics of bank slope hydro-fluctuation belt of Three Gorges Reservoir

Variations of the Three Gorges Reservoir water level, induce degradation on its bank slopes. This may lead to their collapse, which may compromise the operation of the reservoir and compromise the safety of nearby residents and lead to significant economic losses. Therefore, this study aims at characterizing this phenomenon. Firstly, a detailed field investigation of exposed rock masses on typical bank slope of Three Gorges Reservoir Area was carried out at two times, in 2019 and 2023. The in-situ tests of argillaceous siltstone, marlstone and limestone in the water level fluctuating zone were carried out by using three field testing methods, including geological radar, rebound meter and backpack drill, and the deterioration characteristics of rock mass were analyzed, and compared these two on-site tests data. Main research outcomes are: (1) After nearly four years of fluctuations in water level, the degree of degradation of the rock mass on the site has intensified, with an increase in the degradation depth and a decrease in annual strength loss rate. (2) The three types of rock masses tested have different degrees of degradation, with the order of degradation from strong to weak being argillaceous sandstone > marlstone > limestone, fissured rock mass > rock mass of facing water at interlayer > rock mass of facing water at bedding surface. (3) The deterioration of rock mass has obvious temporal and spatial distribution characteristics. The deterioration degree of 30m water level fluctuating zone on the bank slope of the Three Gorges Reservoir Area is different from bottom to top. The deterioration degree of rock mass near the elevations of 145 similar to 146 m, 166 similar to 167 m and 173 similar to 174 m is higher. The research results can provide some basis for disaster prevention and control in the Three Gorges Reservoir Area.