Modeling of Mechanical and Hydraulic Properties of Structured Geomaterials

Abstract

The thesis involves studies of the mechanical and hydraulic behaviour of rock formations used in various geotechnical applications, including underground development, resource extraction, and nuclear waste management. The mechanical response of Cobourg limestone is investigated first. This rock is inherently anisotropic due to stratification as well as the heterogeneity of its fabric, which consists of light grey nodular carbonates and darker argillaceous partings. In this work, a fabric-dependent approach is developed to describe the strength and deformation characteristics of this rock. The study demonstrates that Cobourg limestone can be modeled as a transversely isotropic material by invoking stereological principles and the notion of mean intercept length as a fabric descriptor. The mechanical response is influenced by the spatial variability of argillaceous partings, making the concept of Representative Elementary Volume (REV) inapplicable in most cases. A series of numerical simulations of triaxial tests conducted on differently oriented samples is performed, which highlights the impact of fabric heterogeneity on the mechanical behavior. In addition to studying the mechanical properties of Cobourg limestone, this thesis also addresses the assessment of hydraulic conductivity of sparsely fractured rock masses. Simplified methodologies, such as Oda’s permeability tensor and pipe network models, are compared with a more advanced approach incorporating a constitutive law with embedded discontinuity (CLED). Several numerical examples are provided, examining the fluid flow in discrete fracture networks. The study compares the estimates of principal values and directions of equivalent permeability tensor for different models. Results indicate that the pipe network model, enhanced by an algorithm from graph theory, provides predictions consistent with the CLED approach, particularly for the orientation of principal permeability directions. A pragmatic approach is then proposed on the basis of these findings for the definition of the anisotropic equivalent hydraulic conductivity operator in fractured rock masses.