Rock mass deterioration and its catastrophic effect of karst bank slope in the Three Gorges Project Reservoir area

More than 10 years after the trial impoundment of 175 m asl in the Three Gorges Reservoir area, the rock mass of the karst banks in the water level fluctuation zone in the gorge area deteriorated strongly, and a large number of geological disasters were new-borned or developed acceleratingly, which attracted extensive attention of researchers and the government. From the mesoscopic scale to macroscopic scale and taking the experience gained at some cases and popularizing it in a wide area, this study analyzes the deterioration and catastrophic effect of the karst bank slopes in the Three Gorges Reservoir area through field investigation, laboratory test and analysis. Field investigation shows that the degradation of the karst rock mass is concentrated in the gorge courses of the Three Gorges, Daningriver, among which the Wu Gorge with a total length of about 10 km is the most typical. The degradation mechanism includes the physical mechanism dominated by mechanical transport, the chemical mechanism dominated by dissolution and the mechanical mechanism dominated by stress corrosion fracture. The degradation of the rock mass results in the degradation of the structure of the karst rock mass and the continuous deformation of the local banks. The mutual promotion of deterioration of rock mass-karst hydrodynamic action and bank deformation promotes the occurrence of catastrophe. A large number of field cases show that the early stage of cataclysmic effect caused by the deterioration of the rock mass on the karst bank slopes may be characterized by the tendency of the failure of the shallow mass and the continuous retreat of the bank slopes. The failure modes of the karst bank slopes under the influence of rock mass deterioration include collapse, slide and topple. The degradation of the karst rock mass caused by the fluctuation of water level brings unprecedented threat of high and steep bank slope catastrophe, which may bring the geological disaster of the Three Gorges Reservoir area into a new stage of development and induction. This research may provide technical support for geological disaster early recognition, migration and prevention in the Three Gorges Reservoir area.