Numerical simulation of the failure mechanism of circular tunnels in transversely isotropic rock masses

This paper studies the failure mechanism for a circular tunnel in transversely isotropic rock using the numerical code Realistic Failure Process Analysis (RFPA). In RFPA, an elastic damage model is used to describe the constitutive law of the meso-scale elements, and the maximum tensile strain criterion and the Mohr–Coulomb criterion are adopted as damage thresholds to determine the tensile and shear damage respectively. A series of numerical simulations of the failure process for a plane circular tunnel in rock are conducted. Based on the simulations, two major failure modes around circular tunnels in transversely isotropic rock are numerically reproduced. Whether failure is caused by sliding along the laminated layers depends on the orientation of the laminated layers, the confining pressure, and the strength ratio of the laminated layers to the intact rock. Numerical simulations of the failure modes are given for different ratios of discontinuity strength to intact rock strength, as well as different dimensionless ratios of discontinuity width. Finally, both the failure process of tunnels in up-roll foliated rock masses and down-roll foliated rock masses are investigated by RFPA.