Abstract
Unexploited underground cavities may represent a potential hazard for the surrounding environment when the occurring consequential instabilities augment and propagate upwards toward the surface causing serious damage. Nowadays, North France and its region face a similar risk where large constructed areas, and due to urban expansion, have been extended to surfaces underlain by shallow cavities. Therefore, it is necessary to anticipate and control the circumstances . This work aims to provide an understanding of the deformational behavior of underground cavities on long term process by carrying out a numerical creep analysis of the failure mechanisms. This is performed based using a coupled constitutive law developed to account for the long term degradation phenomenon of the chalk continuum in the presence of joints. Numerical analysis of the time dependant behavior of the underground cavity considering different joint orientations is performed. In addition to visual inspections which remain the most important for the cavity risk assessment, this approach provides comprehensive elements for a better understanding of the progressive failure and thus the temporal aspect of the deformational behavior and failure of underground cavities.
1. INTRODUCTION
Natural and anthropogenic underground cavities may represent a potential hazard for the surrounding environment due to consequential instabilities that might end up with serious damage. Particularly, when these cavities are at shallow depths, the risk that the damage reaches the ground surface is increased due to the upward propagation of localized rupture that might happen. North France and its region are nowadays threatened by such a risk where large built-up areas have been developed in zones underlain by unexploited shallow cavities excavated several decades ago in the existing chalk layers. Hence, this contribution aims to analyze by numerical means, the behavior of these underground cavities and the corresponding failure mechanisms, taking into consideration the effect of time. This latter is represented by the presence of induced fractures which might appear in short term or in long term, and degradation of the chalk which is a time dependent behavior.
