循环荷载下饱和黄土的剪切特性与破坏模式

Investigation on Instability Mode and Shear Behaviour of Saturated Loess Under Cyclic Loading

饱和黄土的破坏模式和剪切特性是分析黄土地基及其构筑物地震变形的基础,为了揭示循环荷载下黄土独特的强度衰减和变形劣化规律,本文开展了饱和黄土不排水动三轴试验,控制初始剪应力(q_(s))和循环剪应力(q_(c)),研究了不同初始应力状态下饱和黄土的动强度、孔压发展规律及破坏模式。试验结果表明:当q_(s)<q_(c)时,重塑和原状黄土试样表现为循环迁移型破坏,当q_(s)≥q_(c)时,重塑黄土试样表现为流动型破坏,而原状黄土试样则表现为塑性应变累积型破坏;黄土试样的循环应力比(R_(CS))、循环阻力比(R_(CR,10))随着初始剪应力比(R_(SS))的增大呈先增大后减小的趋势;循环迁移型和塑性应变累积型破坏在循环加载的初始阶段孔压上升迅速,孔压增长曲线分别呈“风琴”状和“喇叭”状,而流动型破坏的初始阶段孔压增长速率较慢,当到达某一振次后孔压突然增长,孔压增长曲线呈“镰刀”状。基于初始阶段孔压发展指标(K_(1-2))与初始应力状态(q_(s)/q_(c))提出了图表法,可用于预测循环荷载下饱和黄土的破坏模式。

The instability mode and shear behaviour of saturated loess are the basis for analyzing seismic deformation of loess foundation and their structures.To reveal the unique strength attenuation and deformation deterioration of saturated loess under cyclic loads,the dynamic soil strength,development of the pore pressure and instability modes of the saturated loess were investigated by the cyclic triaxial test,subjected to the initial shear stress(q_(s))and the cyclic shear stress(q_(c)).The experimental results show that:When q_(s)<q_(c),the loess samples exhibit the cyclic mobility failure type;When q_(s)≥q_(c),the reconstituted loess samples exhibit the flow failure type,while the intact loess exhibit the plastic strain accumulation failure type.The cyclic stress ratio(R_(CS))and the cyclic resistance ratio(R_(CR,10))of the loess samples increases first and then decreases with the increase of the initial shear stress ratio(R_(SS)).At the initial stage of cyclic loading,the pore pressure in loess samples increases rapidly with the cyclic mobility and plastic strain accumulation failure types,and the pore pressure development curves show the trend of“organ”or“hornt”type.The growth rate of the initial pore pressure in the loess samples with the flow failure type is relatively slow.When the pore pressure reaches a certain cycle,it increases sharply and the pore pressure curve shows a“sickle”type.A chart is established by considering the influence of initial stress state(q_(s)/q_(c))and the initial pore pressure development index(K_(1-2)),it can be used to predict the failure mode of saturated loess under cyclic loading.