循环荷载下液化对土层水平往返变形的影响

采用多工况振动台实验研究液化对土层水平往返变形的影响.以干砂实验为参照,分析孔压增长与土层加速度和土层往返变形之间的关系.结果表明:液化将引起土表加速度显著降低,减小惯性力传递,但同时会引起土层往返剪应变明显增大.对往返变形而言,液化土层往返剪应变就可达到1%～5%的大变形状态,且液化土层往返剪应变沿深度呈下大上小分布.土层中孔压比0.4～0.8是往返变形出现放大的敏感段,在孔压比0.8左右而不是在1.0达到最大.作为其结果,土层液化将对刚性上部结构振动起减震作用,但同时增大的往返剪应变也易导致基础和地下结构破坏,特别是对液化层与下部非液化层交界处的构件更敏感.

Effect of Liquefaction on Cyclic Deformation of Soil Layers

The effects of liquefaction on cyclic deformation of soil layers are investigated by shaking table tests. Taken the dry sand tests as a consult, the relations between the pore water pressure increasing and the accelerations and deformation of the soil layer are presented. The results show that the liquefaction greatly reduces the acceleration amplitude and inertia force of surface ground, meanwhile however, the cyclic deformations of the soil layer increase significantly. The cyclic shear strain in liquefied soil layers can reach 1 %-5% and the strain in the upper layer is less than that in the sub layer. The sensitive range for obvious change of the cyclic deformation appears when the water pressure ratio is about in 0.4-0.8 and reaches the maximum when is about 0.8 rather than 1.0. As a result, the liquefied soil layer reduces the vibration of the rigid superstructure, but the increasing cyclic deformation due to liquefaction can easily destroy the foundation and underground structures, especially for the part of the foundation and underground structures near the interface between the liquefied layer and non-liquefied soil layer.