Modeling of the effects of weakness planes in rock masses on the stability of tunnels using an equivalent continuum and damage model

Abstract

This paper proposes an equivalent continuum model to describe the mechanical behavior of transversely isotropic rocks. In this model, the transverse isotropy of deformation and strength was achieved based on the Mohr–Coulomb and maximum tensile-stress criteria, and the damage was captured by adopting a statistical damage evolution rule. The application of the model is verified through numerical simulation of conventional triaxial tests. The model is then used to reveal the non-uniform mechanical response of the surrounding rock and the secondary lining for a tunnel situated in a weak layered rock mass. The results show that: (1) The proposed model can capture the transverse isotropy in deformation and strength of rocks, and the proposed damage formulation can represent the deterioration and degree of failure of rocks; (2) The fracturing pattern, failure strength and stress–strain curves obtained from the proposed model agree well with test results for three typical rocks with different directional variations in strength; (3) The damage distribution based on the proposed model can identify the failure of layered rock mass; and (4) The damage zones of the surrounding rock and the loads on the secondary lining after tunnel excavation show distinctly asymmetric behavior, that is, the damaged zones are concentrated in the tunnel direction normal to the weak planes, and the positive bending moment and larger axial force are parallel and vertical to the weak planes, respectively.