Abstract: To describe the stress-strain-time behavior of soft clay in projects of excavation,embankment and tunnel,an anisotropic time-dependent model-a trinal-yield-surface model is presented.The model adopts the concept of separating the total deformation into immediate and delayed components.The yield surfaces in p-q　space are one rotated distorted ellipse F and two quasi-Drucker-Prager lines G1 and　G2.F is orientated around the 　k0　consolidation line.The hardening parameters are divided into two parts,which obey volumetric creep rule and deviatoric creep rule,respectively.The stress state can be in four situations—elastic,semiplastic on F,semiplastic on G,or fully plastic according to the place of the stress point in stress space.And the constitutive equations corresponding to the four stress states are obtained.In order to simulate creep rupture of soft clay,a microstructure-based damage law is presented and incorporated into the time-dependent model.The model is numerically implemented to simulate undrained creep behavior of anisotropic soft clay.A good correlation between the numerical predictions and the experimental results is observed.