Damage Creep Constitutive Model of Carbonaceous Slate with Different Moisture Content

To explore the creep characteristics of carbonaceous schist under different moisture content conditions, based on the indoor graded loading creep test data, this paper constructed a viscoplastic body capable of describing the nonlinear accelerated creep stage throughout the entire creep process. This is achieved by parallelly connecting a nonlinear viscous element with a plastic element that characterizes yield behavior, based on data from indoor graded loading creep tests. Subsequently, this nonlinear viscoplastic body was integrated in series with the classical Nishihara model. By incorporating the softening patterns of elastic modulus and viscosity coefficient, four damage factors were introduced to establish a damage-based creep constitutive model (i. e., an improved Nishihara model) that describes the entire creep process of carbonaceous slate under different moisture content conditions. Through secondary development of a user-defined material subroutine (UMAT) in ABAQUS finite element software, numerical simulations of triaxial creep tests on carbonaceous slate under varying moisture content conditions were implemented. The applicability of the model was validated by comparing experimental creep data from rock samples with numerical simulation results. The research results show that the constructed improved Nishihara model can significantly improve the simulation accuracy in the accelerated creep stage. The graded loading creep test curves under different moisture content conditions are in good agreement with the numerical simulation curves, and the correlation coefficients are all greater than 0.9. The numerical simulation cloud map accurately reproduced the creep deformation evolution process of rock samples with different water contents, verifying the correctness and effectiveness of the proposed creep constitutive model of carbonaceous shale considering water damage and the development of the UMAT subroutine. This research achievement can provide theoretical support for the long-term stability assessment and disaster early warning of deep-water buried carbonaceous slate tunnel projects.