Stability of D-shaped tunnels in a Mohr–Coulomb material under anisotropic stress conditions

Abstract

The near-face stability of D-shaped tunnels excavated in a Mohr–Coulomb material subjected to anisotropic in situ stress conditions is investigated in the present study. The construction of the intake tunnel of the Darlington Nuclear Generating Station is analyzed using three-dimensional elasto-plastic finite element analysis. The induced displacement and stresses around the tunnel opening as the face advances are compared to the field measurements recorded during the tunnel excavation. The effect of rock mass strength reduction on the tunnel deformation, face stability, and distribution of stresses at the tunnel circumference is investigated for different in situ stress conditions. When the ratio of rock mass strength to overburden pressure falls below 0.5, excessive deformation occurrs and squeezing of the rock mass becomes a problem that can cause instability of both the tunnel circumference and the face.Key words: weak rock, tunnelling, horizontal stresses, three-dimensional, finite element, excavation, face stability.