Progressive Damage of a Canadian Granite in Laboratory Compression Tests and Underground Excavations

Abstract

The crystalline rock formations of the Canadian Shield are currently one candidate rock type for the geological disposal of radioactive waste in Canada. This article starts with a critical review of past research results on the geomechanical behaviour of Lac du Bonnet granite, a rock type found at an Underground Research Laboratory (URL) in Pinawa, Manitoba, Canada. Based on the published data, a constitutive model was developed, based on Mohr-Coulomb plasticity, which includes the concept of asynchronous degradation of cohesion and mobilization of friction with progressive damage, as well as time-dependent degradation of strength. The constitutive model was used to simulate laboratory compression tests. It was then implemented in a coupled hydro-mechanical model to simulate the response of the rock mass induced by excavation of a test tunnel at 420 m depth at the URL.