Evolution of plastic zone in surrounding rock of roadway within anisotropic stratum under complex in-situ stress

Deep mining operates under complex high in-situ stress conditions where the inherent anisotropy of rock strata, caused by bedding planes and random joints. However, most existing studies on this plastic zone assume isotropic strata, which substantially deviates from real engineering conditions. Based on an improved anisotropic Mohr-Coulomb failure criterion, an analytical solution for the plastic zone under anisotropic conditions is derived. Comparative analyses-through both theoretical and numerical simulations-between anisotropic and isotropic cases confirm the considerable impact of bedding planes and joints on the plastic zone. The evolution and characteristics of the maximum principal stress and plastic zone are systematically investigated under varying in-situ stress conditions for three joint configurations: single-set joints, multi-set orthogonal joints, and multi-set non-orthogonal joints. The results reveal that for roadways with a single-set joint, the plastic zone approximates a banded distribution aligned with the joint dip direction. In multi-joint roadways, the plastic zone transitions from a hexagonal to an "X" shape as the joint dip angle increases. Furthermore, with an increasing lateral pressure coefficient, the plastic zone in orthogonally jointed strata evolves from "butterfly" to "horizontal line," "cross," "vertical line," and finally an "X" shape. A case study validating the model against field observations of roadway deformation and failure in anisotropic strata demonstrates that the extension direction of the plastic zone aligns with the joint orientation, exhibiting distinct asymmetric large deformation. The close agreement between numerical simulations and field measurements substantiates the reliability of the proposed model.