列车荷载引起心形应力路径下软土非共轴应变特征研究

Strain characteristics of non-coaxiality under heart- shaped stress path caused by train loads in soft clay

采用空心圆柱仪对重塑空心软黏土试样开展了一系列非破坏试验,研究了列车循环动荷载作用下的性状。试验中主要选取心形应力路径,以圆形应力路径为辅助,对比分析了两种应力路径下软土的非共轴应变特征,探究循环振次对非共轴特性的影响、荷载频率的大小对非共轴角与大主应力方向角关系曲线形态变化的影响,同时进行了机制分析,并与另一动应力水平下试验结果进行了对比论证。此外,在不考虑频率影响下建立了简化的非共轴角与大主应力方向角之间的关系模型。研究发现,在大主应力方向角旋转的任意周期内,心形与圆形两种应力路径下非共轴角随大主应力方向角变化趋势各自有明显特点,相同动应力水平下两种应力路径产生的偏应力增量引起的单位偏应变增量大小也有所区别,但在大主应力方向角旋转的局部角度内,两种应力路径下的偏应变增量相近;心形应力路径下的非共轴角以及偏应力增量引发的单位偏应变增量大小受循环振次的影响不明显,任意振次中大主应力方向角在[-30°,40°]弧度区间内对应的偏应变增量远大于该区间之外的偏应变增量;随着频率增大,非共轴角随大主应力方向角的变化呈现越来越明显的波动。

To study the behavior of soft clay under cyclic train loads, a series of non-destructive tests on remolding hollow cylinder samples is conducted using hollow cylindrical apparatus. Most of the tests are in the heart-shaped stress path and some are in the round stress path as assistant. The strain characteristics of non-coaxiality under the two kinds of stress path are compared with each other. The effects of vibration cycle times N on non-coaxiality and the influence of frequency f on the shape of curves between non-coaxial angle β and major principal stress directional angle a, are studied. The analysis of mechanism is carded out and the test results under the other dynamic stress level are compared with the former tests. In addition, a simplified model of relation between β and ασ taking no account off is established. The research shows that during any cycle of ασ the relations between β and ασunder the two stress paths have their own characteristics. And unit deviator strain increments caused by deviator stress increments （dε/ds） under the two stress paths at the same dynamic stress level are different from each other. However, during some section of eta, the dε/ds under the two stress paths are close to each other. The impacts of N on β and dε/ds under the heart-shaped stress path are slight. ddds is much larger in the angle section [30°, 40°] of ασ than the other section during any vibration cycle time. The curves between β and ασfluctuate violently with thefinereasing.