Cavity expansion into two different concentric regions of rock masses

Building a house near a cliff, digging a tunnel through a mountain or build a road on a desert all require the same guaranty: knowing the behaviour of the soil under a certain stress. As we know, the behaviour of soil under a certain stress has always been an important subject of interest because of the security aspects it provides. The achievement of projects implying the expansion of soil requires a good prediction of the behaviour of the rocks. The subject that is going to be described hereafter is the analysis of the cavity expansion into two different regions of rock masses. The final goal of our work is to analyze the behaviour of stresses and displacements of the soil within two rock masses that form our system. Many theories under the mechanism of failure have been developed, one of them being the well-known Mohr-Coulomb’s law, but many others exist because different situations often require different theories. In this thesis, the whole development is based on the well-known Hoek-Brown failure criterion. Because the cavity expansion takes place in rock material, this criterion allows to take account of the joints and imperfections in the rock. In order to analyze this bilayer expansion, the first part of our work is to develop the mathematical equations for a finite monolayer rock in elasticity and plasticity. After that, an extension for a bilayer model is put in place. In order to do this, an analysis of different scenarios was necessary. Indeed, in a system containing two different rocks, it is possible for the pressure applied in the system to put one rock in elasticity while the other one is put in plasticity. This is why a diagram representing all cases has been drawn as the skeleton of our research. After that, with this analytical model, many different simulations are made in order to analyze the variations of the main Hoek-Brown parameters. Once this is done, a verification takes place thanks to numerical simulation using the software Plaxis.