Formulation and implementation of elastoplastic constitutive model for carbonaceous slate

Carbonaceous slate is a typical transversely isotropic material. A reasonable constitutive material model is essential for the accurate prediction of mechanical response of underground structures that cross the carbonaceous slate layer. The conventional triaxial compression test results show that physical properties of carbonaceous slate are nonlinear and highly related to the bedding dip angle. As such, this paper presents a transversely isotropic elastoplastic constitutive model for carbonaceous slate. The elastic regime of constitutive material model is described by generalized Hooke’s law, and the elastic stiffness matrix in the off-axis coordinate system is derived. The yield criterion considered in this study is derived based on the Mclamore and Gray criterion. The conventional triaxial compression tests of carbonaceous slate with different bedding dip angles under different confining pressures are carried out. All the material parameters required by the constitutive model can be obtained by conventional triaxial compression tests. The proposed constitutive material model is implemented by means of the subroutine UMAT in the commercial software ABAQUS. The effectiveness of the proposed constitutive material model is validated by comparing the experimental test results and finite element simulation results, and the excavation process of Baoligang tunnel is modeled as a case study.