3D face effects of tunnels misaligned with the principal directions of material and stress anisotropy: Fid-Bau Portal

3D face effects of tunnels misaligned with the principal directions of material and stress anisotropy

Vitali, Osvaldo P.M. / Celestino, Tarcisio B. / Bobet, Antonio

Highlights • Far-field shear stresses occur when tunnels are misaligned with principal stresses. • Far-field axial shear stresses induce axial deformations in tunnels. • In anisotropic ground, tunnel misalignment causes asymmetric deformations. • Liner loads are asymmetric as a result of the tunnel misalignment.

Abstract Rock masses may present remarked stress anisotropy or fabric structure, such as foliation and bedding; thus, it is likely that a tunnel is misaligned with the geostatic principal stress directions, with the principal material directions, or with both. Anti-symmetric axial displacements and axial shear stresses are induced as a consequence of the tunnel misalignment. However, the effects of the misalignment near the face are still unknown. In this paper, the 3D face effects on tunnels misaligned with the geostatic principal stress directions and/or with the material principal directions are investigated. 3D FEM modeling is conducted for unsupported and supported tunnels. A transversely anisotropic elastic model is selected to represent the structured rock mass. The results show that misaligned tunnels undergo asymmetric deformations near the face. The radial deformations far-behind the face are symmetric for unsupported tunnels, but they are asymmetric for supported tunnels. The reason for this is that asymmetric deformations near the face affect ground-support interaction. As a consequence, the internal forces in the tunnel support are also asymmetric; further, the support forces may be larger than those of a tunnel aligned with the geostatic principal stress.