Coupled hydromechanical analysis in the presence of discontinuities

Abstract

In this thesis, a new continuum framework for the coupled hydromechanical analysis of fractured porous media is proposed. This formulation represents an extension of the constitutive law with embedded discontinuity (CLED) for the assessment of both hydraulic and mechanical properties in the regions intercepted by discontinuities. The constitutive relations governing the hydromechanical response are derived by averaging the fluid pressure gradient and the discontinuous displacement fields over a selected referential volume of the material, subject to some physical constraints. Within this approach, an internal length scale parameter is employed in the definition of the equivalent hydraulic conductivity as well as the tangential stiffness operators. An evolution law is derived governing the variation of hydraulic conductivity with continuing deformation in order to explicitly account for the hydromechanical coupling. The governing field equations are formulated following the general form of balance equations in the superimposed interacting continua. An enhanced mixed u-p finite element formulation is presented which considers the effect of progressive evolution of the fracture aperture in the weak statements of balance equations. Fully implicit temporal discretization is employed, and the finite element formulation is stabilized by invoking the Polynomial-Pressure-Projection (PPP) technique. The proposed methodology is verified by a comprehensive numerical study dealing with a steady-state flow through fractured media, time-dependent consolidation in the presence of a discontinuity, 3D simulation of an axial splitting test carried out on a saturated sample under displacement and fluid pressure controlled conditions, and assessment of the evolution and coalescence of localized damage zones in sparsely fractured crystalline rocks. Both discrete and smeared damage tracing strategies have been employed. For the discrete damage tracing in the compression regime, the bifurcation analysis has been carried out. A comprehensive CLED-FE code based on the proposed approach, and an analogous IE-FE code, have been developed for the coupled hydromechanical analysis of porous media.