Tunnel Misalignment with Geostatic Principal Stress Directions in Anisotropic Rock Masses

O.P.M. Vitali, T.B. Celestino, A. Bobet


Soils and Rocks, São Paulo, 43(1): 123-138, January-March, 2020 | PDF


Rock masses may present pronounced stress anisotropy, and so it is likely that a tunnel is misaligned with the geostatic principal stress directions. As a consequence, anti-symmetric axial displacements and axial shear stresses are induced around the tunnel due to the presence of far-field axial shear stresses. Limited research has been conducted on the effects of far-field axial shear stresses on tunnel behavior. This paper investigates the effects of tunnel misalignment with the geostatic principal stresses in anisotropic rock masses. 3D FEM modeling of a tunnel misaligned 45° with the principal horizontal stresses is conducted. An anisotropic geostatic stress field is considered, with the major horizontal stress two times larger than the vertical stress and the minor horizontal stress equal to the vertical stress. The anisotropic behavior of the rock mass is represented by a transversely anisotropic elastic model, with properties typical of anisotropic rock masses. Tunnels in horizontally and vertically-structured rock masses are assessed. Unsupported and supported tunnels are investigated. The results show that asymmetric deformations and asymmetric stresses are induced near the face of the tunnel as a result of the tunnel misalignment with the geostatic principal stresses and with the rock mass structure. These asymmetric deformations near the face affect the ground-support interaction such that the internal forces in the liner are also asymmetric.

Submitted on September 28, 2019; Final Acceptance on February 13, 2020; Discussion open until August 31, 2020.
DOI: 10.28927/SR.431123