Abstract: In this paper, a series of triaxial tests under coupled cyclic-seepage loads were carried out for saturated soft clay in Tianjin. The results show that the development of cumulative plastic strain is characterized by three stages: initial instantaneous growth, decelerated increase and stable / linear development, and seepage can enlarge the dynamic deformation up to 1-2 times of that compared to cyclic load only. Larger seepage force induces greater cumulative plastic deformation. The lower frequency or greater cyclic stress amplitude induces larger strain. The prediction model of cumulative plastic deformation of soft clay is established under the condition of dynamic- seepage coupling. The presence of seepage induces greater inclination to strain axis of hysteric curve at initial vibration. The dynamic elastic modulus of soft clay increases first and then decreases, and the larger seepage force induces lower modulus; the mathematical relationship between dynamic elastic modulus and cumulative plastic strain is revealed: under seepage condition, a prediction model of dynamic modulus was proposed considering the influences of seepage force and frequency. The damp ratio decreases to a constant value with increasing number of cycle. The larger the seepage force is, the larger the damping ratio attenuation amplitude is, and the damping ratio is approximately 0.02-0.04 at the end of the vibration. The results could provide guidance on the numerical simulation of dynamic characteristics of soft clay ground under seepage condition.

Key words: soft clay, dynamic-seepage coupling, cumulative plastic strain, seepage, dynamic modulus, damping ratio