土石坝拟静力抗震稳定性分析与坝坡地震滑移量估算

Analysis and evaluation of pseudo-static aseismic stability and seism-induced sliding movement of earth-rock dams

单独采用拟静力抗震稳定性安全系数,并不能准确地评价土石坝的动力稳定性,Newmark等采用刚塑体滑移量或永久变形评价土石坝地震稳定性的建议得到了逐步认同,但土石坝地震永久变形或滑移量的估算尚缺乏合理方法。为此,将土石坝地震动力响应分析和拟静力极限平衡分析相结合,提出了合理地估算坝坡上潜在滑坡体地震滑移量的数值计算方法。首先,根据土石坝地震动力响应分析,针对圆弧滑动面和非圆弧光滑渐变曲面形式滑动面,分别采用简化Bishop法及改进的简化Bishop法计算坝坡上潜在滑动体的各个时刻拟静力安全系数。随后,对其中安全系数小于1的瞬时超载阶段,通过时间积分确定潜在滑动体的滑移量。最后,结合算例并通过具体数值计算与分析探讨了竖向地震动分量、滑坡体竖向地震响应、振动孔隙水压力等各种因素对土石坝地震位移及抗震性能的影响。

It has been well recognized that the safety of embankments during earthquake cannot be evaluated solely by the safety factor of the pseudo-static stability. It is suggested by Newmark that the seismic stability of embankment should be assessed by using the seism-induced sliding movements or permanent deformations instead of the overall safety factor, However, the rational evaluation of sliding movements or residual deformations induced during earthquake cannot be made in a perfect manner. In this paper, a numerical procedure is proposed for evaluating the sliding movements of embankments based on the step-by-step dynamic response analysis and the pseudo-static limit-equilibrium analysis. In the proposed method, the dynamic responses of embankments to earthquake shaking are first predicted by FEM-based numerical analysis. The simplified Bishop＇s procedure and modified simplified Bishop＇s procedure of limit equilibrium are employed to evaluate the transient safety factors of potential sliding mass of embankment slopes respectively for circle slip surface and for smoothed non-circle slip surface. For the overloading in which the transient safety factor is lower than unity; the transient sliding movement can be assessed by double integration with respect to time. For the example case, the parametric computations and comparative studies are made to examine the effect of vertical component of ground motions, vertical seismic response of potential sliding mass, shaking-induced pore water pressure and other related factors on the sliding movement and earthquake-resistant behavior of embankments.