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Web End = Rock Mech Rock Eng (2016) 49:18491873 DOI 10.1007/s00603-015-0847-2
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Web End = Hybrid Finite-Discrete Element Simulation of the EDZ Formation and Mechanical Sealing Process Around a Microtunnelin Opalinus Clay
Andrea Lisjak1 Bryan S. A. Tatone1 Omid K. Mahabadi1 Giovanni Grasselli8
Paul Marschall2 George W. Lanyon3 Rmi de la Vaissire4 Hua Shao5
Helen Leung6 Christophe Nussbaum7
Received: 13 February 2015 / Accepted: 6 September 2015 / Published online: 16 September 2015 Springer-Verlag Wien 2015
Abstract The analysis and prediction of the rock mass disturbance around underground excavations are critical components of the performance and safety assessment of deep geological repositories for nuclear waste. In the short term, an excavation damaged zone (EDZ) tends to develop due to the redistribution of stresses around the underground openings. The EDZ is associated with an increase in hydraulic conductivity of several orders of magnitude. In argillaceous rocks, sealing mechanisms ultimately lead to a partial reduction in the effective hydraulic conductivity of the EDZ with time. The goal of this study is to strengthen the understanding of the phenomena involved in the EDZ formation and sealing in Opalinus Clay, an indurated claystone currently being assessed as a host rock for a geological repository in Switzerland. To achieve this goal, hybrid nite-discrete element method (FDEM) simulations are performed. With its explicit consideration of fracturing
processes, FDEM modeling is applied to the HG-A experiment, an in situ test carried out at the Mont Terri underground rock laboratory to investigate the hydro-mechanical response of a backlled and sealed microtunnel. A quantitative simulation of the EDZ formation process around the microtunnel is rst carried out, and the numerical results are compared with eld observations. Then, the re-compression of the EDZ under the effect of a purely mechanical loading, capturing the increase of swelling pressure from the backll onto the rock, is considered. The simulation results highlight distinctive rock failure kinematics due to the bedded structure of the rock mass. Also, fracture termination is simulated at the intersection with a pre-existing discontinuity, representing a fault plane oblique...