Etude expérimentale et numérique du comportement mécanique des roches dures soumises aux contraintes mécaniques et aux hautes températures

Abstract

This thesis deals with two important topics in rock mechanics and their applications in mining engineering. Firstly, the effect of mechanical load and thermal treatment on hard rock’s specimen is numerically and experimentally investigated. We have considered three types of rocks: granite, sandstone and gneiss. Based on Newton’s second law, we established the rate- equation model of rock specimen under uniaxial mechanic load and fire. We introduced in the model the material nonlinear stress/strain relationship and the effect of material non linearity is analyzed. We show numerically that globally, the amplitude of the internal stress gradually decreases when the temperature increases. The analysis of the internal stress reveals that the combined effect of the thermal treatment and mechanical load on the specimen lead to the rapid damage of the specimen. The material non linearity parameter slowly affects the thermal destruction of the rocks. Experimental results show that as the hard rock loses its rigidity when temperature increases, fire reduces the mechanical performance of the rocks significantly. Moreover, we find that after being submitted to temperature up to 600°C, the mechanical energy necessary to fragment rocks can be reduced up to 50%. Secondly, numerical analysis of underground structures, considering the transverse isotropy system of rocks was done using CAST 3M code by varying the shape of excavation and the coefficient of earth pressure ’k’. The magnitude of horizontal stress obtained for the horse shoe shape excavation is lower than the magnitude obtained for circular, rectangular, trapezium, vault hole. Therefore, we have concluded that the horse shoe shape offers the best stability and the best design for engineer. Numerical results revealed that the magnitude of redistribution of horizontal stresses obtained for transverse isotropic rock is less than those obtained in the case of isotropic rock. The more the rock has the anisotropic behavior, the more the mass of the rock around the tunnel is stable.