主应力轴旋转对地铁荷载作用下 软黏土累积变形的影响

为了定量评价主应力轴旋转对地铁荷载作用下隧道下卧软黏土累积变形的影响，通过有限元方法并结合实测数据的验证对地铁荷载下地基土的应力路径进行分析；在此基础上，借助空心圆柱仪对这一复杂应力路径进行室内模拟和对比试验研究。结果表明：主应力轴旋转增大了软黏土的累积变形，且最大有效主应力比（有效最大主应力与有效最小主应力之比）越大、或加载频率越高增大更明显。在实际地铁荷载和通常隧道埋深条件下，考虑主应力轴旋转使软黏土的累积变形增加9%～23%（加载频率越高，增加越大）。可用常规循环三轴的累积变形试验结果乘以土体分别在有、无主应力轴旋转下变形的比值，来预估实际地铁荷载下软黏土的累积变形，初步研究得到该比值与土体的最大有效主应力比之间存在幂函数关系。

Influences of rotation of principal stress axis on accumulative deformation of soft clay under subway cyclic loading

In order to investigate the influences of continuous rotation of principal stress axis on the accumulative deformation of soft clay lying below subway tunnel under subway dynamic loading, the finite element method (FEM) combined with field measurement data is used to analyze the complex stress path in subsoil induced by subway loading, and then the hollow cylinder apparatus (HCA) is used to simulate the stress path in laboratory and to carry out comparison tests. Experimental results show that: the continuous rotation of principal stress axis increases the accumulative deformation of soft clay; and the effect is more significant at higher effective principal stress ratio (i.e. the ratio of the effective maximum principal stress to the effective minimum principal stress) or loading frequency. Under the realistic subway loading and the usual tunnel depth, the continuous rotation of principal stress axis magnifies the accumulative deformation of soft clay between 1.09 and 1.23 times (the higher the loading frequency is, the greater the magnification is). The actual accumulative deformation of soft clay under the realistic subway loading (i.e. with continuous rotation of principal stress axis) can be estimated by multiplying the accumulative deformation obtained from traditional cyclic triaxial tests (i.e. without principal stress axis rotation) by the ratio of axial strains between tests with and without principal stress axis rotation. The preliminary study shows there exists power function between the ratio and the maximum effective principal stress ratio of soil.