Underground Rock Dissolution and Geomechanical Issues

Many soluble rocks will dissolve when in contact with fluid such as water. This transformation of rock solid into flowing fluid may trigger the creation of cavities which may further lead to either smooth subsidence or sudden collapse of land surface. Dissolution phenomenon can be of natural or human origin. This paper deals with the problem of the dissolution of underground soluble rocks and the geomechanical consequences such as subsidence, sinkholes and underground collapse. In this paper, rock dissolution and the induced underground cavities are computed using a Diffuse Interface Model, which does not require to follow interfaces explicitly. We describe briefly the mathematical and physical framework for the dissolution model. We first explain the transition (upscaling) of a multiphysics problem formulated at the microscopic (pore-) scale level to the macroscopic (Darcy-) scale level. Rock material considered in this paper is gypsum, despite that the developed method is also suitable for over soluble rocks (e.g., limestone, Halite). The second part of this paper is devoted to a set of problems dealing with mechanical response of the rock mass in connection with the dissolution process. We discuss the subsidence induced by the dissolution of one or more gypsum lenses, the stability of the covering, and finally the failure of a gypsum pillar in an abandoned quarry. These examples, while they may involve rather theoretical hypotheses, have the virtue of showing the relevance of the method as well as the very diverse issues that it can treat.