Modelling of the hydromechanical response of a shaft sinking in a deep claystone
Résumé
In the framework of the feasibility study of a radioactive-waste repository in a geological formation, Andra (French radioactive waste management agency) has been built an underground research laboratory within a Callovo-Oxfordian argillite formation located in Eastern France. During the sinking of the laboratory's access shaft, the hydromechanical behaviour of the argillites was monitored through an in situ experimental program called REP. The experimental zone is located between 460 and 476m depth. From a drift located at -445 m, 15 instrumentated boreholes were drilled downwards and equipped with 120 mechanical and hydraulic sensors. A predictive modelling of the shaft sinking has been performed in the framework of the European Modex-Rep project, using a poro-elastoplastic model based on a generalized Hoek and Brown criterion. Results of blind prediction emphasize that the model reproduces the in situ phenomena, but is not able to reproduce the amplitude of the drop in pore pressure during the shaft sinking. This article presents the analysis of this discrepancy and discusses new approaches aimed at improving the previous model. Finally, permeability changes around the shaft based on the in situ measurements and/or damage-induced permeability changes implemented in the model allow to better reproduce in situ data.