Study on rational procedures to evaluate seismic stability of retaining walls

为了建立合理的挡土墙抗震稳定性评价方法，对1995年兵库县南部县地震破坏的铁路路堤挡土墙进行了反分析，对各种挡土墙进行了振动台模型试验和倾斜台模型试验，并对高地震荷载水平下的主动土压力进行了研究。反分析结果表明，现行的挡土墙拟静力抗震设计方法所采用的设计水平系数与1995年兵库县南部县地震中多个挡土墙所经历的重力加速度除以峰值地面加速度之间存在较大差距。在倾斜台试验中，无论墙的类型如何，在回填土中形成一个或一组与回填土的主动破坏相关的破坏面，随后仅在略大的倾斜角时墙才最终破坏或坍塌。另一方面，在振动台试验中，墙体的最终破坏或倒塌发生在较晚的阶段，墙体在填土中出现第一个活动破坏面后发生较大的变形和位移，在此基础上，提出了一种修正的拟静力极限平衡法来计算高地震荷载水平下的主动土压力。虽然它与Mononobe-Okabe方法相似，但它考虑了回填土中应变局部化的影响，以及与之相关的峰后剪切阻力沿先前形成的破坏面上从峰值到残余值的减小。

In order to establish rational procedures to evaluate seismic stability of retaining walls, back analyzes of retaining walls for railway embankments damaged by the 1995 Hyogoken-nanbu earthquake, shaking and tilt table model tests on a variety of retaining walls, and investigations to evaluate active earth pressures at high seismic load levels were conducted.The back analyzes revealed that there exists a big gap between the design horizontal coefficients used in the current pseudo-static seismic design approaches for retaining walls and the peak ground acceleration divided by the gravitational acceleration experienced by a number of RWs during the 1995 Hyogo-ken-nambu Earthquake. In the tilt table tests, irrespective of wall type, a failure plane or a set of failure planes developed in the backfill associated with the active failure in the backfill, followed by the ultimate failure or collapse of wall only at a slightly larger tilting angle. On the other hand, in the shaking table tests, the ultimate failure or collapse of wall occurred at a much later stage associated with relative large deformation and displacement of wall occurring after the first active failure plane developed in the backfill.Based on the above results, a modified pseudo-static and limit-equilibrium approach to evaluate active earth pressure at high seismic load levels is proposed. Although it is similar to the Mononobe-Okabe method, the proposed method considers the effects of strain localization in the backfill soil and associated post-peak reduction in the shear resistance from peak to residual values along a previously formed failure plane.