Analytical and Numerical Simulations to Predict the Long-Term Behavior of Lined Tunnels Considering Excavation-Induced Damaged Zone

Tunnels embedded in soft rock masses experience time-dependent behaviour, and designing an appropriate supporting system is a challenging task. This condition can be more problematic when a damaged zone is also developed (due to poor quality blasting). In this paper, a theoretical solution is presented to predict long-term tunnel convergence and long-term induced lining pressure, considering the existence of an altered zone due to excavation. The rheological behaviour of rock mass and the altered zone is simulated by viscoelastic behaviour obeying the Burgers model. It is also assumed that a continuous lining, i.e., a shotcrete layer, is placed (with elastic behaviour) to confine the convergence. A comprehensive parametric study is performed by the presented solution to evaluate the effects of various parameters on the induced lining pressures and the tunnel convergence. Then, to have more practical conditions, the elastic-viscoplastic rheological model (known as CVISC) is assigned to the rock mass to consider its failure. The problem is further studied by only numerical approach using FDM. The results show that the support installation time and the radius of the altered zone have remarkable effects on the output results.