Studying the air ventilation effect on the hydromechanical behaviour of cracked rock media around large-scale gallery using a double-scale FE2 model

Abstract

The interaction between rock and the atmosphere occurs through air circulation within underground galleries, thereby affecting the hydromechanical long-term behaviour of the rock in the vicinity of galleries and its drainage. To study this air-rock interaction, a coupled hydromechanical model within a double-scale finite element framework is improved to simulate partial saturated cases at small scale in the crack network. The capillary water distribution at the microscale is not modelled. The introduction of the capillary pressure is therefore realised from a macroscopic phenomenon consideration, but it depends on the evolution of the mesoscopic structure and geometry (as the normal opening of mineral contacts) inside 2D Representative Elementary Areas. The gas flow is also neglected by assuming a constant gas pressure. Then, the developed model is applied to model an underground gallery ventilation process, which is reproduced with constant air relative humidity inside the gallery and classical imposition at the gallery wall. The numerical simulation results show that long-term gallery air ventilation induces a drainage of the liquid water present in the rock towards the gallery that leads to an obvious desaturation process close to the gallery wall. Furthermore, the gallery air ventilation inhibits the development of shear strain localisation around the gallery.