Time-dependent modeling of supported drifts excavated in Callovo-Oxfordian claystone considering the excavation-induced fractured zone

Abstract

Drifts have been excavated in Callovo-Oxfordian claystone to test the feasibility of deep geological disposal of radioactive waste. The time-dependent behavior of these structures has been observed to be significantly impacted by the development of excavation-induced fractured zones around the drifts. A numerical model is proposed to simulate the response of drifts excavated in various conditions and the obtained results are compared to in-situ data. This model is based on the explicit introduction of an anisotropic excavation-induced fractured zones following the extension observed in situ and the implementation of a visco-elasto-plastic model (CVISC) for the rock mass using the FLAC3D numerical code. The model reproduces the anisotropic distribution and evolution of the rock mass deformation, which tends to accumulate within the excavation-induced fractured zones. The influence of the extension of the fractured zone on the response is investigated through a sensitivity analysis. It shows that the variability of the measured convergence data can be reproduced by using fractured zone extensions that are consistent with the ones observed in situ. Also, various support scenarios are modeled. Flexible supports lead to low radial confinement levels, while stiffer supports provide greater confinement, significantly reducing the strain rates in the rock mass. The model is able to simulate multiple drift configurations and orientations using a simple approach and accurately reproduce the field observations. This suggests that this approach is a useful tool for designing tunnels excavated in COx claystone and for evaluating the long-term response.