Approaches for representing hydro-mechanical coupling between sub-surface excavations and argillaceous porous media at the ventilation experiment, Mont Terri

At the Mont Terri Underground Research Laboratory (Switzerland), a field-scale investigation has been conducted in order to investigate the hydro-mechanical and chemical perturbations induced in the argillaceous formation by forced ventilation through a tunnel. This experiment has been selected to be used for processing model development and validation in the international project DECOVALEX-2011. The conceptual and mathematical representation of the engineered void, which itself forms a major part of the experiment and is not simply a boundary condition, is the subject of this paper. A variety of approaches have been examined by the contributors to DECOVALEX and a summary of their findings is presented here. Two major aspects are discussed. Firstly, the approaches for the treatment of the surface condition at the porous media/tunnel interface are examined, with two equivalent but differing formulations successfully demonstrated. Secondly, approaches for representing the tunnel with associated air and water vapour movement, when coupled with the hydro-mechanical (HM) representation of the porous medium, are also examined. It is clearly demonstrated that, for the experimental conditions of the ventilation experiment (VE) that abstracted physical and empirical models of the tunnel, can be used successfully to represent the hydraulic behaviour of the tunnel and the hydraulic interaction between the tunnel and the surrounding rock mass.