Abstract: A series of undrained cyclic triaxial tests were performed on a typical Shanghai soft clay.Both the initial static deviatoric stress and the cyclic stress level were analyzed varied.It was shown that the cumulative plastic strain depended not only on the applied cyclic stress and number of cycles,but also on the initial static deviatoric stress level.Based on the concept of critical state soil mechanics,a new parameter called relative deviatoric stress level was introduced considering the effects of initial static deviatoric stress,cyclic deviatoric stress and undrained deviatoric stress at failure.The cumulative plastic strain was found to be closely related to this parameter..