考虑强度退化效应的堤坝抗震稳定性评价方法

考虑土的动强度随振动孔隙压力上升的衰减效应,将拟静力极限平衡分析和滑动体位移分析相结合,提出了堤坝抗震稳定性评价方法.首先,基于土工动力有限元分析,确定坝坡潜在滑动土体的平均加速度时程,进而,基于拟静力概念,采用极限平衡分析,确定坝坡的安全系数随时间的变化历程,其中当安全系数瞬时小于1时,表明坝坡在地震中处于瞬时超载状态,采用Newmark刚体滑块模型估算瞬时超载所产生的滑动位移,将各个超载阶段的滑动位移叠加,求得设计地震动作用下堤坝边坡的累积滑移量,根据这种方法所进行的数值计算与分析表明,考虑强度循环退化效应后所得到的坝坡滑移量更为合理.

Evaluation of aseismic stability of soil embankments considering cyclic degradation of soil strength

A simplified procedure for evaluating asismic stability of embankments subjected to earthquake shaking, in which the degradation effect of undrained strength of soils due to generation and building-up of pore water pressure induced by cyclic loading is taken account. In the proposed method, the average seismic acceleration of potential sliding soil mass in embankment slope is determined by the dynamic analysis based on finite element method. Then the limit equilibrium analysis and the pseudo-static concept are combined together to define the variation of overall safety factors of the given potential sliding soil mass with time. Afterwards, the sliding movements caused by the transient overloading when overall safety factor is lower than unity is assessed by using the rigid-sling block model developed by Newmark (1965). Finally, the transient movements are accumulated for all the overloadings. The dynamic stability of embankment slope can be evaluated on the basis of the computed accumulative sliding movements induced by earthquake. The numerical computations are performed by using the proposed procedure. It is shown that the computed sliding displacements for a given embankment, in which cyclic degradation of soil strength is properly considered, is more rational compared with the conventional computational results.