Abstract：Based on the creep curves of soft rock under uniaxial compression，a damage variable and a hardening function are introduced into creep model to express the nonlinear creep behavior of soft rock. A new nonlinear model for axial and lateral creep is established for soft rock. The typical creep curve can be divided into three phases，which are decelerating creep phase，even creep phase and accelerating one. The hardening of viscosity coefficient is the main cause of the decelerating phase of creep；and the accelerating phase is mainly due to the damage of the elastic modulus. The damage mechanism and the hardening one keep its balance in the even creep phase. It is unreasonable to describe and explain the three-phase creep by using the nonlinear viscosity coefficient only or the damage of elastic modulus. The three-phase creep course is the results of the competition between damage and hardening. With the creep development of soft rock，rock microstructure changes influence upon the mechanical behavior. Those changes are explained by nonlinear damage and hardening variables. A nonlinear creep model is constructed which can describe the three-phase axial creep of soft rock. Furthermore，the creep Poisson¢s ratio is introduced into creep model to express the lateral creep behavior of soft rock；and the energy damage variable is used to describe the anisotropic elastic damage. The results of the model and tests for mudstone and red sandstone are perfectly fitted.
