Abstract: To describe the creep mechanical behavior of rocks, triaxial compression creep tests of sandstone under different confining pressures are conducted herein. Results show that the steady creep stage is a process of developing and expanding microcracks in rocks, and the steady creep rate and confining pressure increase the power function. The long-term strengths of sandstone under confining pressures of 5 MPa, 10 MPa, and 15 MPa are 19.8 MPa, 22.3 MPa, and 24.7 MPa, respectively. The long-term strength increases with the increase in confining pressure. Based on the nonlinear characteristics of rock creep, the viscoelastic modulus E（p） associated with confining pressure is defined. E（p，t） that can reflect the influence of rock creep by time and confining pressure is obtained using the derivation transformation, which is applied to the improved Burgers model to obtain a new one-dimensional creep constitutive model. It can be extended to three-dimensional stress state to obtain a new three-dimensional nonlinear mechanical model, identify creep test data, compare and analyze the prediction results, and prove the feasibility and rationality of the model. The research results shed light on the simulation of creep behavior of rock under three-dimensional stress state.

Key words: sandstone, creep rate, long-term strength; viscoelastic modulus, three-dimensional model