Long-Term Analysis of Tunnels in Rheological Rock Masses Considering the Excavation-Damaged Zone

According to the excavation methods of tunneling, a damaged zone may be developed in the rock mass around the tunnel, the mechanical properties of which can be significantly altered. This issue is of great importance in the analyses of both the short-term and the long-term performance of tunnels. In this paper, a closed-form solution is presented to find the long-term-induced stresses and the convergence of the tunnel considering the altered zone development. To account for the time-dependency effect, the Burgers viscoelastic rheological model is assigned to altered and unaltered zones. The proposed method is applicable for the case in which the tunnel excavation is halted or for the case in which the tunnel is continuously excavated. The predictions made by the proposed analytical method are compared with those made by using FLAC(3D) software. Then, a parametric study is performed to investigate the effects of different key parameters associated with the research aim. Finally, the numerical simulation is extended so that the combining Burgers substance and the Mohr-Coulomb failure criterion (CVISC) model, i.e., a viscoplastic rheological model, is adopted to the medium. The results indicate a remarkable difference between the predictions of tunnel convergence by the Burgers and the CVISC models, in very severe and extreme squeezing conditions.