单向循环荷载作用下饱和软黏土的性状研究

摘要

模拟交通荷载的作用,对珠江三角洲地区的高液限饱和软黏土和低液限饱和软黏土分别进行单向加载的循环三轴试验,研究饱和软黏土在压缩循环荷载下的轴向累积应变和累积孔压的发展情况,并充分考虑轴向循环压力大小、围压与塑性指数等因素对饱和软黏土性状的影响.试验结果表明:(1)单向循环荷载作用下,饱和黏土存在着临界循环应力,对于同一种土、不同围压下的临界循环应力,可引入临界循环应力比,用饱和黏土在各个围压下的不排水强度对临界循环应力进行归一化处理.(2)临界循环应力比的大小与饱和黏土的塑性指数有关,塑性指数越大,临界循环应力比越小.(3)循环应力大于临界循环应力时,累积轴向应变与累积孔压随循环次数变化的曲线是破坏型的.(4)循环应力小于临界循环应力时,累积轴向应变与累积孔压随循环次数变化的曲线是衰减型的,在相同的加载条件下,塑性指数大的试样累积变形和累积孔压均比塑性指数小的累积变形和累积孔压发展得快.(5)在单向循环荷载作用下,饱和黏土破坏时,孔压均没有达到围压值,只有围压的60％～70％.该研究成果可为交通荷载作用下软土地基沉降分析提供有益的参考.%High liquid limit and low liquid limit clay specimens from Pearl River delta are used for cyclic triaxial tests under uniaxial cyclic loading, respectively, to simulate traffic loads. The emphasis is put on the development of axial strain and pore pressure of saturated soft clay. The influence of axial stress, confining stress and plasticity index are taken into account. The results of tests indicate that: (1) For the same soil, there are different critical cyclic stresses of saturated soft clay under different confining pressures. Critical cyclic stress ratio can be introduced under uniaxial cyclic loading. The critical cyclic stress can be normalized with undrained shear strength of saturated soft clay under different confining pressures. (2) Whether the cyclic stress is greater than the critical cyclic stress, variations of axis strain and pore pressure with number of cycles show two kind of rules. (3) The critical cyclic stress ratio is related to the plasticity index of saturated soft clay. The greater the plasticity index is, the smaller the critical cyclic stress ratio is. (4) When the cyclic stress is less than the critical cyclic stress, with the same loading condition, the axis strain and the pore pressure of samples with greater plasticity index develop faster than those of samples with smaller plastic index. (5) When the cyclic stress is greater than the critical cyclic stress, the sample of saturated soft clay fails rapidly. When the sample fails, the pore pressure can not achieve the value of confining pressure, only 60% - 70% of the confining pressure. These conclusions are helpful for analyzing the settlement of saturated soft foundation under traffic loading.