交通荷载引发主应力轴旋转下软黏土变形与强度特性试验研究

交通、波浪、地震等循环荷载引发不同主应力方向变化模式，对软土地基长期沉降与稳定产生显著影响。为研究饱和软黏土在交通荷载下的长期动力特性，借助空心圆柱扭剪仪开展偏应力空间中主应力轴心形线旋转、圆形旋转与定向剪切等3类主应力方向变化路径的室内模拟，对比研究了不同试验条件下试样不排水塑性累积变形、孔压、临界动应力比与动强度特性的发展规律，研究表明：（1）不同主应力轴旋转路径下土体临界应力比由低到高依次为主应力轴圆形旋转、主应力轴心形旋转、拉压非等幅三轴路径。与前面临界应力比分布相对应，在轴向累积应变稳定型中，产生的塑性累积变形与极限孔压依次减小；（2）振次大于一定数值时，不同主应力方向变化路径下稳定型试样的轴向累积应变与时间的对数具有良好的线性关系，并依此建立了轴向塑性累积变形方程；（3）与轴向塑性累积变形相对应，动力荷载下土体孔压增长也存在3种发展规律，主应力轴连续旋转路径下临界型破坏的土体孔压-应变时程曲线呈三阶段两相态点模式；（4）在其他条件均相同时，土体在主应力轴圆形旋转路径下强度最小，在主应力轴心形旋转路径下的次之，在拉压非等幅动三轴路径下最高。

An experimental study of the deformation and strength characteristics of soft clay under principal stress axis rotation caused by traffic load

Cyclic loadings such as traffic loads, wave loads and earthquake can cause principal stress rotation, which has a significant impact on the long-term settlement and stability of soft ground. In order to study the long-term dynamic characteristics of saturated soft clay under the traffic load, a series of hollow cylinder shearing experiments is performed on the soft soil by adopting three types of principal stress paths including heart-shaped line rotation, circular rotation and directional shear in deviatoric stress space. The undrained cumulative plastic deformation, pore pressure, critical dynamic stress ratio and dynamic strength characteristics are compared among specimens under different experimental conditions. The results show that (1) the critical stress ratio increases, in order, from circular rotation, heart-shaped line rotation and unequal amplitude in tension, to triaxial compression. Accordingly, the cumulative plastic deformation and pore pressure limit decrease in turn for the stable cumulative stage of axial strain. (2) When the vibration times is greater than certain values, the axial cumulative strains of the stable-type specimens have good linear relationships with the logarithm of time under different principal stress rotation paths. Based on this, the cumulative axial plastic deformation equation is developed. (3) Along with the cumulative axial plastic deformation, the pore pressure growth in the soil under different dynamical loadings also shows three kinds of development trend. A three-stage and two-phase mode is found in the pore pressure-time curve and the strain-time curve under the principal stress axis rotation path. (4) When the other conditions are the same, the strength of soil under heart-shaped rotation is higher than that under the circular rotation, and lower than that under the unequal amplitude in tension and compression of triaxial path.