Analytical model and stability of surrounding block rock mass around deep tunnels

Deep rock mass has a typical inhomogeneous and discontinuous self-stressed block-hierarchical structure. Without considering the blocky characteristics of deep rock mass, the classical continuum theory fails to analyze the stress field of the block rock mass around deep tunnels. The failure mode of the deep block rock mass around deep tunnels is the shear slip along weak contact surfaces between rock blocks. The plane strain model of block rock mass around a deep tunnel is established. The analytical expressions of interaction between rock blocks on the contact surface are obtained in the axial symmetric problem. The supporting forces of deep tunnels are obtained by assuming that the weak contact satisfies the rigid-plastic and Mohr-Coulomb constitutive relationships respectively. Through comparison of the calculated results based on the block rock mass model and the continuum rock mass model, the necessity of the consideration of the blocky characteristics in the construction and theoretical analysis of deep tunnels is validated. The radial displacement, shear stress and shear slip are obtained by supposing that the shear stress and the shear slip of contact satisfy the piecewise-linear relationship. The dimensionless stability parameter λ of block rock mass around deep tunnels is defined, the block rock mass around deep tunnels is stable when λ <1, and when λ >1, the surrounding block rock mass is unstable.