1.Sclool of Highway, Chang’an University, Xi’an 710064, China;

2.Key Laboratory for Bridge and Tunnel of Shaanxi Province, Chang’an University, Xi’an 710064, China;
3.School of Architecture and Civil Engineering, Xi'an University of Science and Technology, Xi'an 710054, China

To investigate the creep characteristics of carbonaceous slate under different moisture content conditions, based on the creep test data of indoor graded loading, a nonlinear viscous element was connected in parallel with a plastic element characterizing the yield characteristics to construct a viscoplastic body that can describe the nonlinear accelerated creep stage throughout the creep process. The nonlinear viscoplastic body was connected in series with the classical Nishihara model. Four damage factors were proposed based on the softening laws of elastic modulus and viscosity coefficient.  A damage creep constitutive model was established to describe the entire creep process of carbonaceous slate under different moisture content conditions. The subroutine (UMAT) was developed using ABAQUS finite element software, and numerical simulations of triaxial creep tests of carbonaceous shale under different moisture contents were achieved. The applicability of the model was verified by comparing the creep test and numerical simulation results of rock samples. Research has shown that the improved Nishihara model constructed can effectively improve the simulation accuracy of the accelerated creep stage. The graded loading creep test curves under different moisture content conditions are in good agreement with the numerical simulation curves, with correlation coefficients above 0.9. The numerical simulation cloud map accurately reproduced the creep deformation growth of rock samples with different moisture contents, verifying the correctness and effectiveness of the proposed creep constitutive model for carbonaceous shale considering moisture damage and the development of UMAT subroutine. The research results can provide a theoretical basis for the long-term stability assessment and disaster early warning of tunnels in deeply buried water-rich carbonaceous slate.