La fragmentation naturelle des massifs rocheux : modèles de blocs et bases de données tridimensionnelles : réalisation, exploration géométrique et applications

摘要

Knowledge of the three-dimensional fractured medium is based on direct and indirect observation of one- or twodimensional extracts. The difficulties of visualization in 3 dimensions and the constant existence of geometrical gaps are major handieaps for the understanding of complex laws ruling fractured rock medium fracturing. Numerical "equivalent" models separately give mechanical, hydraulic, or thermal answers to particular problems of fractured networks. However, a large number of physical properties of the rock solid mass are conditioned by geometry and topology of the fractured system, which remains a fundamental question. Our model OBSIFRAC (OBject SImulator for rock FRACturing) deals with this essential aspect. In a brittle deformation context, the observation of natural sections justifies that discontinuities can be represented by plane and inter-connected surfaces, without free terminations, limiting convex polyhedra. Consequently, the network can be seen as a puzzle of blocks. This assumption enabled us to build a three-dimensional database of the network, which describes in an exhaustive way the geometrical components of the puzzle (fractures, blocks, faces, edges and vertices). Starting from an initial seed point, the fragmentation process affects one or more blocks, possibly composed of several elementary polyhedra. Orientation and position of the fractured plans can be defined in a stochastic, statistical or deterministic way. Two applications are studied.The first proposes a 3D extrapolation of the fractured volume around a cored drilling well, in the granite of Soultz-sous-Forêt, France. With a simplified friction model, the second application shows the contribution of the model in studying block equilibrium in a rocky escarpment.