EFFECT OF PORE FLUID DIFFUSION ON DEFORMATION AND FAILURE OF ROCK.

The presence of pore fluid in laboratory rock samples or fissured rock masses can substantially alter the response to applied or induced loads and the conditions for failure. Pore fluid effects have been proposed as playing a role in a wide variety of geophysical and geotechnical phenomena. The most familiar effect of the pore fluid is is to reduce the effective value of the mean normal compressive stress. Coupling of deformation with pore fluid diffusion also introduces time dependence into the response of an otherwise rate-independent solid. An elastic fluid-infiltrated solid responds more stiffly to deformations that are rapid compared to the time scale of diffusion than for deformations that are slow compared to the diffusion time. Because many geological materials change volume when sheared inelastically, pore fluid diffusion can also be coupled to inelastic deformation. This review considers the mechanical effects of pore fluid on the deformation and failure of geological and geotechnical materials. Applications to brittle rock and, more specifically, to earth faulting are emphasized.