STUDY OF CHARACTERISTICS OF SATURATED SOFT CLAY UNDER UNIAXIAL CYCLIC LOAD

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.