大型水库区桥基边坡稳定性与失稳运动特征

Stability and motion characteristics of bridge slope in the large reservoir area

我国西南山区已建成众多大型水库,库岸边坡在降雨、库水周期性涨落、地震等复杂地质条件作用下易发生滑坡。若公路桥梁基础位于库岸边坡变形或失稳影响范围内,可能对桥墩产生巨大的侧向荷载,从而危害基础结构乃至桥梁整体安全,而针对该问题研究较少。以白鹤滩库区小江特大桥桥基边坡为例,应用GeoStudio分析桥基边坡在库水涨落、降雨、地震联合作用下的稳定性;针对库水涨落联合降雨工况下的欠稳定边坡,采用TsunamiBalls(TB)数值方法模拟滑坡堆积体失稳下滑冲击桥墩的动力学过程,分析桥墩受到的动态冲击荷载。研究表明:(1)库水升降是影响边坡稳定性的主要因素;(2)施加地震荷载后边坡稳定性系数大幅降低,而降雨对稳定性系数影响有限;(3)滑体对桥墩的冲击荷载随时间先增大再减小,期间会出现3次主要荷载峰值,其中最大冲击荷载13890kN,出现在滑体最大运动速度之后,滑体冲击质量最大的时刻。库岸桥基边坡在库水位涨落条件下稳定性明显降低,TB模拟滑体失稳冲击过程可能造成桥基结构破坏。研究结果可为大型水库边坡和公路桥梁防灾减灾及安全运营提供技术参考。

Lots of large reservoirs have been built in the southwest mountainous areas of China,and the slope of reservoir shore is prone to landslides under complex geological conditions such as rainfall,reservoir water periodic fluctuation and earthquake.If the highway bridge foundation is located in the range of bank slope deformation or instability,huge lateral load may be generated on the bridge pier,thus endangering the foundation structure and the overall safety of the bridge.Taking the slope of Xiaojiang Bridge in Baihetan Reservoir as an example,this study applied GeoStudio to analyse the stability of bridge foundation slope under the combined condition of reservoir water fluctuation,rainfall and earthquake.As to the unstable slope under the combined rainfall condition of reservoir water fluctuation,the numerical method of Tsunami Balls(TB)was used to simulate the landslide dynamic process and evaluate the dynamic impact load of the bridge pier.The results show that the slope stability coefficient decreases due to the reservoir water fluctuation,which is the main factor affecting the slope stability.After seismic load is applied,the slope stability coefficient decreases sharply,while rainfall has limited influence on the stability coefficient.The impact load of the sliding body on the bridge pier increases first and then decreases with time,and the maximum impact load is 13890 kN,which appears after the maximum velocity of the sliding body.It is concluded that the stability of the bridge foundation slope on the bank of reservoir is reduced dramatically under the influence of reservoir water fluctuation,and the failure of the bridge foundation structure may be caused by the instability impact process of TB simulated sliding body.This study provides technical information for the disaster prevention and reduction and safe operation of large reservoir slopes and highway bridges.