A MODEL FOR COUPLED MECHANICAL AND HYDRAULIC BEHAVIOR OF A ROCK JOINT

Constitutive laws for rock joints should be able to reproduce the fund amental mechanical behaviour of real joints, such as dilation under sh ear and strain softening due to surface asperity degradation. In this work, we extend the model of Plesha(1) to include hydraulic behaviour. During shearing, the joint can experience dilation, leading to an ini tial increase in its permeability. Experiments have shown that the rat e of increase of the permeability slows down as shearing proceeds, and , at later stages, the permeability could decrease again. The above be haviour is attributed to gouge production. The stress-strain relations hip of the joint is formulated by appeal to classical theories of inte rface plasticity. It is shown that the parameters of the model can be estimated from the Barton-Bandis empirical coefficients; the Joint Rou ghness Coefficient (JRC) and the Joint Compresive strength (JSC). We f urther assume that gouge production is also related to the plastic wor k of the shear stresses, which enables the derivation of a relationshi p between the permeability of the joint and its mechanical aperture. T he model is implemented in a finite element code (FRACON) developed by the authors for the simulation of the coupled thermal-hydraulic-mecha nical behaviour of jointed rock masses. Typical laboratory experiments are simulated with the FRACON code in order to illustrate the trends predicted in the proposed model. (C) 1998 by John Wiley & Sons. Ltd.