多级拼装悬臂式挡墙地震响应振动台模型试验

Shaking table model test study on seismic responses of assembled multi-step cantilever retaining walls

多级拼装悬臂式挡墙是一种可用于高填方工程的新型轻型支挡结构。为确定墙–坡系统的地震动力响应特征,进行几何、重度和时间相似比分别为1∶10,1∶1和1∶3.162的三级拼装悬臂墙支挡边坡的水平振动台模型试验。结果表明:坡体加速度沿墙高呈明显的非线性放大效应;墙后静止土压力和动土压力均呈"三峰型"分布模式,各级墙踵板对其下部墙背土压力存在遮蔽效应,动土压力沿墙高呈显著的多段折线型分布模式;在地震波波峰时刻,墙体位移急剧增大并接近永久位移;地震作用过程中墙–坡系统的变形发展可分为PGA≤0.4 g时的多级墙体微小变形、0.4 g<PGA<1 g时的最下一级墙体水平向显著滑移、PGA≥1 g时的墙–坡系统大变形共3个阶段;墙–坡系统的失稳破坏可相应分为3种模式:最下一级墙沿墙底水平滑移、中下级墙后土体滑移–拉裂和全墙–边坡系统整体滑动。基于此破坏模式,采用拟静力法对墙–坡系统地震整体稳定性进行了分析,实例计算表明,简化Bishop法和传递系数法所得的墙–坡整体稳定系数相近,均比Fellenius法大3%~13%,且此偏差随PGA增大而显著。

Assembled multi-step cantilever retaining wall is one of new types of light retaining structures suitable for high fill earthworks.In order to determine seismic responses of the wall-slope system,horizontally shaking table model tests of assembled three-step cantilever retaining walls supporting a fill slope were conducted with geometry,gravity and time similarity ratios of 1:10,1:1 and 1:3.162 respectively.The results show that the acceleration of the wall-slope system has obviously nonlinear amplification effect upwards along the wall.Both static and dynamic earth pressures on the walls are generally distributed in a trimodal model.Except for the highest-step wall,there is reduction effect of the earth pressure at each wall top due to the shielding action of the nearby heel plates inserted in the filling soil.Distribution of the dynamic earth pressure is commonly multi-segment polyline.At the moment of the peak acceleration of input seismic waves,wall displacements are sharply rising and almost close to their permanent values.During the process of strong seismic action,deformation development of the wall-slope system can be divided into 3 stages including slight deformation of each wall under PGA≤0.4 g,visibly horizontal movement of the lowest-step wall under 0.4 g<PGA<1 g,as well as seriously high displacements of all walls under PGA)1 g.Correspondingly,the failure mode of the wall-slope system can be classified as three types covering horizontally sliding failure of the lowest-step wall along its bottom,shear-tension failure of the filling soil behind the lower walls,together with overall slide failure of the wall-slope system.Based on the overall failure mode determined by the tests,stability analysis of the wall-slope system was carried out according to the pseudo-static approach.Analysis results of a practical example indicate that the factors of safety under various earthquakes by simplified Bishop method and transfer coefficient method are almost equal to each other and about 3%-13%higher than that obtained by Fellenius method.The difference is increasing with rising PGA.