New modeling approach for tunnels under complex ground and loading conditions

Abstract The behavior of tunnels in anisotropic rock masses is highly complex and heavily dependent on the orientation of the tunnel axis with respect to the geostatic principal stress directions and to the rock structural planes. 2D solutions cannot capture the 3D face effects of such complex scenario; thus, 3D numerical modeling is required. The modeling of such tunnels using conventional boundary conditions may be cumbersome since the tunnel may not be parallel to the boundaries. The issue is further complicated if the principal far-field stresses are not parallel to the principal axes of material anisotropy. In this case, the use of conventional boundary conditions may be problematic. In this paper, a new approach is presented to impose the boundary conditions and the far-field stresses on 3D numerical models of tunnels under complex ground and loading conditions. With the proposed approach, it is possible to easily simulate any orientation of the tunnel with respect to the principal directions of stress and material anisotropy. The numerical results obtained with the proposed approach were validated with an analytical solution and with numerical results using traditional boundary conditions.