Sensitivity analysis and probabilistic study on temporal evolution of the EDZ around a deep tunnel

Abstract
The finite element code Cast3M is used to perform a 2D numerical simulation of the mechanical behaviour of deep underground tunnels with a special emphasis on a sensitivity analysis and probabilistic study of time-dependent development of the Excavation Damage Zone (EDZ). The damaged zone refers to the volume of rock in which cracks become important, thereby deteriorating its mechanical and hydraulic properties. The rock mass behaviour is assumed as elasto-viscoplastic in which the viscoplasticity is modelled by means of the Perzyna’s overstress concept. First, stress-based and strain-based criteria are compared to find an appropriate criterion to estimate the damaged zone evolution. Then, a sensitivity analysis and probabilistic study of several key parameters are performed on the progressive development of the damaged zone. The numerical results show that a strain-based criterion seems more realistic to estimate the damaged zone, in which the material is considered damaged if its equivalent strain in the sense of von Mises exceeds a critical strain threshold. The backfill-vacuum-rate and the value of the critical strain parameter also have an important influence on the extension of the damaged zone. The conclusions provide some guidelines for the design of underground openings.