Rock mass deterioration and its catastrophic effect of karst bank slope in the Three Gorges Project Reservoir area
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摘要: 三峡工程库区175 m试验性蓄水10 多年后，峡谷区岩溶岸坡水位变动带岩体劣化强烈，新生或加速形成了大量地质灾害，引起研究人员和政府的广泛关注。文章从微细观到宏观、由点到面，采用野外调查、室内试验分析了三峡库区岩溶岸坡岩体劣化及其灾变效应。野外调查显示，溶蚀岩体劣化集中发育于三峡、大宁河等干支流峡谷区域，其中以巫峡共约10 km长的岸坡最为典型。溶蚀岩体劣化机制包括以机械搬运为主的物理机制、以溶蚀/溶解为主的化学机制和以应力腐蚀断裂为主的力学机制。岩体劣化导致溶蚀岩体结构降级，岸坡局部持续形变。岩体劣化、岩溶水动力作用、岸坡形变相互促进，推动了岸坡灾变的发生。大量案例表明，岩溶岸坡岩体劣化引起灾变效应早期，破坏浅表层、岸坡不断后退。岩体劣化影响下岩溶岸坡破坏模式包括崩塌、滑移和倾倒3种主要类型。库水位长期变动导致的溶蚀岩体劣化带来了前所未有的高陡岸坡灾变威胁，可能将三峡库区地质灾害带入新的发育阶段。本研究将为三峡库区岩溶地质灾害隐患点识别与防灾减灾提供技术支撑。Abstract: 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.
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