| In this dissertation, a phenomenological damage constitutive theory for brittle solids progressively failing through the growth, nucleation, and coalescence of microdefects is developed. This theory is based on irreversible thermodynamics with internal state variables representing irreversible microstructural rearrangements, and experimental observations on geomaterials. The effect of these structural changes in such materials is incorporated in the theory and is quantified by a continuum variable, called a damage variable. A vector valued internal state variable is introduced to represent average material degradation. A novel damage evolution law based on both microscopic and macroscopic experimental observations of geomaterials is proposed. It is shown that damage formation is responsible for strain-softening, for the degradation of stiffness, for positive dilatancy, and for induced anisotropy. A finite element code incorporating damage mechanics and coupled to fluid flow is formulated using Gurtin's variational principle equivalent to the governing equations for coupling nonlinear deformation with flow.;The predictive capabilities of this phenomenological damage model have been demonstrated in a series of qualitative and quantitative comparisons with available experimental data for various rocks and concrete under tensile and compressive stresses. In addition, some numerical predictions of the problem of a finite load on an infinite damaged medium with fluid flow are compared with published analytical solutions and with results from a linear poroelasticity approach to the same problem.;The results presented in this dissertation show that the proposed theory can replicate the salient aspects of the mechanical behaviour of brittle geomaterials. Particularly, strain-softening, positive dilatancy, decrease of elastic modulus, and confining pressure effects on geomaterials observed in laboratory are well captured. It is also shown that damage growth contributes significantly to the diffusion of pore pressure in coupling deformation with pore pressure diffusion processes. |
