Study on dynamic stress-strain relationship of soft clay based on modified Iwan’s model under undrained cyclic loading

Degradation will occur in soft clay under cyclic loading because of the generation of pore pressure and the rearrangement of soil particles.At the meantime,cumulative plastic strain will develop.It is observed that the development of cumulative plastic strain is accelerated under the initial deviator stress,and the hysteresis loops move rightward clearly with the progressive number of cycles.An empirical degradation model of normally consolidated soft clay subjected to undrained cyclic stess controlled triaxial test was proposed at different numbers of cycles,cyclic stress levels and initial deviator stresses.And then,the empirical model was incorporated into Iwan’s series-parallel model to account for the cyclic degradation.Simultaneously,an ideal plastic element was introduced to simulate the development of cumulative plastic strain during cyclic loading.Subsequently,the dynamic stress-strain relationship of saturated soft clay was described with modified Masing’s rules.Compared with the experimental data and other models,the present model was proved to be reasonable and effective.