The use of two-part Hooke’s model (TPHM) to model the mine-by test at Mont Terri Site, Switzerland

Abstract

The full-scale mine-by (MB) test conducted in 2008 in the Mont Terri underground rock laboratory (Switzerland) investigated the deformation and the coupled hydro-mechanical behavior of the Opalinus Clay in response to tunnel excavations. The Opalinus Clay is currently under investigation in Switzerland as a potential host rock for geologic disposal of high-level radioactive waste. To further improve the understanding and modeling of the coupled processes and their impact on the performance of a geologic repository in Opalinus Clay, a newly developed two-part Hooke’s model (TPHM) was implemented into a geomechanical simulator. A three-dimensional simulation model based on the TPHM was then developed to predict the deformation and pore pressure responses in the near field of the MB Niche 2 test at the Mont Terri Site. The usefulness and validity of the TPHM are demonstrated by the consistency between simulation results and field observations. Simulation results show that the pore pressure disturbance becomes visible at about 11m ahead of the mine-by excavation advancing face (along the longitudinal direction of the MB Niche). The results also demonstrate that there exists a good correlation between the excavation damage zone (EDZ) and the pore-pressure evolution, which may have important practical implications for monitoring EDZ evolution with pore-pressure sensors. The simulation results, which are sensitive to the constitutive relationships used in the model, capture both the observed displacements and the size of the damage zone, whereas the approach based on the conventional Hooke’s law underestimates both. The comparison between simulated and observed results also indicates that laboratory-measured mechanical properties can be used to accurately predict field-scale mechanical deformations, as long as valid constitutive relationships are employed.