STUDY ON STRAIN SOFTENING MODEL OF SATURATED SOFT CLAY UNDER CYCLIC LOADING

Degradations of stiffness and strength will occur in soft clay under cyclic loading because of the generation of pore pressure. Unfortunately,previous work rarely incorporates the effect of anisotropic consolidation on cyclic degradation behavior of soft clay. In addition,most of the previous tests were performed with a lower cyclic frequency when considering strain softening. The strain degradation characteristics of saturated soft clay subjected to undrained cyclic triaxial loading is investigated at different cyclic numbers,cyclic stress ratios,consolidation ratios,overconsolidation ratios and frequencies of cyclic loading. It is observed that the degradation index reduces with the progressive cyclic numbers and the increase of cyclic stress ratio. There is a critical cyclic stress ratio in clay subjected to cyclic loading. When the cyclic stress ratio is much higher or lower than the critical cyclic stress ratio,the relationship between degradation index and lgN is linear. However,when the cyclic stress ratio is around critical cyclic stress ratio,a nonlinear relationship is observed. On the other hand,higher frequency and overconsolidation ratio decrease the degradation index of soft clay. For anisotropic consolidated clay,the degradation index reduces with the increase of consolidation ratio at a lower cyclic stress ratio. At a higher cyclic stress ratio,the degradation index of anisotropic consolidated clay will be greater than that of normally consolidated soils with increasing cyclic numbers. A nonlinear relationship is obtained if the degradation index is plotted against the cyclic numbers on a semi-log scale. This relationship has been synthesized in the form of an empirical equation. This empirical equation is further used to describe the dynamic stress-strain relationship of saturated soft clay according to modified Iwan′s model.