库水—降雨作用下靠椅状基覆面堆积层滑坡响应机理

Coupled influence of reservoir water and rainfall on the response mechanism of accumulated landslides with chair-like interfaces between sliding masses and bedrock

为研究库水—降雨联合作用下库岸涉水靠椅状基覆面堆积层滑坡响应机理,以奉节县藕塘滑坡为例,采用监测数据分析、相关性理论及离散元数值模拟方法,揭示了藕塘滑坡变形规律及可能的失稳机制。结果表明:藕塘滑坡变形在分区和分期上分别具有随高程增加变形速率增大和随时间增长累计位移呈阶跃式迭代增加的特点;库水和降雨被认为是藕塘滑坡地表变形的重要影响因素,库水对滑坡变形影响主要集中在前部区域且其诱发滑坡变形机制为渗透诱发,降雨则主要集中在中部及后部区域且其诱发滑坡变形机制由初期的吸水膨胀转变至渗透诱发,库水—降雨联合作用下藕塘滑坡极有可能出现前部牵引—后部推移的渐进式失稳破坏。

[Objective]The Three Gorges Reservoir(TGR)Dam is currently the largest hydroelectric power project in the world.TGR has a daily power output of 9.81×109 kWh and a reservoir capacity of 3.92×1010 m3.It was completed in Southwest China in 2009 and the reservoir water was impounded to 175 m.Consequently,a long and narrow hydro-fluctuation belt(over 600 km,from 145 m to 175 m),which extends from Yichang City in Hubei Province to Maoer Gorge in Chongqing Municipality,China,appeared along the TGR.The completion of the TGR Project and the subsequent impoundment of the 660 km-long reservoir reactivated and induced over 5000 landslides along the banks of the reservoir.These landslides have posed great threats to residences,shipping along the Yangtze River,and dam stability.Thus,gaining insights into the behavior,triggering and conditioning factors,and evolutionary mechanism of these reservoir-induced landslides is crucial for landslide control,management,and decision-making.Water,including fluctuations in reservoir water levels and periodic rainfall,is one of the most common triggering factors for bank slope failures.Variations in reservoir water levels can affect slope stability during the drawdown and impoundment stages.Furthermore,rainfall can trigger slope failure events,including shallow and deep-seated landslides on slopes along the reservoir.Although the individual effects of rainfall or reservoir water on bank slope stability have been widely studied,the combined effects of rainfall and reservoir water on landslide deformation have been rarely discussed.Moreover,many reservoir-induced landslides have been triggered by the coupled effects of rainfall and reservoir-level fluctuations.This study aims to study the coupled influence of reservoir water and rainfall on the response mechanism of accumulated landslides with chair-like interfaces between sliding masses and bedrock.[Methods]The Outang landslide,a typical landslide with a chair-like interface between the sliding mass and bedrock,was selected as the research object.Monitoring data analysis,correlation theory,and discrete element method were adopted to reveal the deformation characteristics and possible failure evolution mechanism of landslides.[Results]Research results revealed that from a regional perspective,the landslide deformation rate increased with the increase in elevation,whereas from a temporal perspective,landslide deformation showed a step-like increase.Reservoir water and rainfall were considered the main triggering factors of landslide deformation.Reservoir water affected the front of the landslide with a corresponding seepage-induced deformation mechanism,whereas rainfall affected the remaining part of the landslide,and its corresponding movement mechanism transformed from water swelling during the initial period of rainfall to the seepage-induced mechanism.[Conclusions]The landslide exhibited composite push-retrogression-type failure evolution with fluctuating reservoir levels destabilizing rock masses toward the front section and precipitation mainly mobilizing materials in the upper section of slopes.This research will further elucidate the reactivated ancient landslide issues,such as deformation characteristics and failure evolution,and provide practical experience and insights regarding analogous old landslides in the reservoir area.