基于超载法的拱坝坝肩地震动力稳定性方法研究

Research on seismic dynamic stability of arch dam abutment based on overload method

拱坝坝肩地震动力稳定性一直是工程界关注的一大热点,然而对坝肩动力稳定性的评判方法和标准的研究还不成熟。为完善坝肩动力稳定分析方法,将有限元法与刚体极限平衡法的优势相结合,提出了地震动力超载方法以及极限累积位移评判标准。首先,基于有限元法开展实时动力分析,对坝肩可能的滑移块体采用多重网格应力插值求任意时刻的阻滑力和下滑力,确定其主滑方向,而后采用刚体极限平衡法计算每个滑块的动安全系数;同时,对瞬时动安全系数小于1.0的时段,进行加速度积分,求出滑块累积失稳位移。结合滑块尺寸及滑动面强度参数提出极限累积位移计算公式作为失稳判据,通过比较累积位移与极限累积位移判定滑块的稳定性。基于以上思路开发了一套坝肩动力稳定分析系统SAFEDAM。以沙牌拱坝经受反映5.12地震的人工波为例,开展了沙牌拱坝坝肩动力超载稳定分析,验证了极限累积位移判据的合理性。研究表明,沙牌左岸坝肩超载稳定安全倍数K_(p_0)=3.2,右岸坝肩超载稳定安全倍数K_(p_0)=4.2。工程实例计算表明,该方法计算坝肩动力稳定性使用较为方便可靠,具有较大的工程实用价值,为坝肩动力稳定性分析和评价提供了一条新路径。

Seismic dynamic stability analysis of arch dam abutment has been a hot topic in geotechnical engineering. However, studies are not yet mature on the evaluation methods and criteria of dam abutment dynamic stability. The advantage of the finite element method and limit equilibrium method are combined to improve the abutment dynamic stability analysis method. Then the seismic dynamic overload method and limit cumulative displacement criterion are proposed. Firstly, a real-time dynamic analysis is conducted based on the finite element method. Secondly, multi-grid method is adopted to calculate the resistance force and sliding force of abutment potential slip blocks through stress interpolation, it can determine the main sliding direction and calculate the dynamic safety factor using the limit equilibrium method for each slider. Meanwhile, there is an acceleration integral to get the cumulative displacement of slip blocks for the period within which the safety factor is less then 1.0. According to the slider size and the sliding surface strength parameters, the limit cumulative displacement formulation is proposed and acted as the instability criterion of slip blocks; by comparing the cumulative displacement and the limit cumulative displacement, the stability of the slider is determined. An abutment dynamic stability analysis system SAFEDAM is established from the above ideas. To verify the rationality of the limit cumulative displacement criterion, Shapai arch dam is taken as example which has underwent the Wenchuan 5.12 earthquake in Sichuan province. The results show that for the left bank abutment of Shapai arch dam, the overload stability safety factor K_（p_0） is 3.2, while for the right bank the K_（p_0） is 4.2. The example study confirms that the proposed method provides a new path for the dynamic stability of arch dam abutment and evaluation. For the reliability and flexibility to assess the dynamic stability analysis, the method shows its wide applicability in engineering practice.