A model for coupled mechanical and hydraulic behaviour of a rock joint

Abstract

SUMMARYConstitutive laws for rock joints should be able to reproduce the fundamental mechanical behaviour of real joints, such as dilation under shear and strain softening due to surface asperity degradation. In this work, we extend the model of Plesha to include hydraulic behaviour. During shearing, the joint can experience dilation, leading to an initial increase in its permeability. Experiments have shown that the rate of increase of the permeability slows down as shearing proceeds, and, at later stages, the permeability could decrease again. The above behaviour is attributed to gouge production. The stress-strain relationship of the joint is formulated by appeal to classical theories of interface plasticity. It is shown that the parameters of the model can be estimated from the Barton-Bandis empirical coefficients; the Joint Roughness Coefficient (JRC) and the Joint Compresive strength (JSC). We further assume that gouge production is also related to the plastic work of the shear stresses, which enables the derivation of a relationship between the permeability of the joint and its mechanical aperture. The model is implemented in a finite element code (FRACON) developed by the authors for the simulation of the coupled thermal-hydraulic-mechanical 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.

Thermo-hydro-mechanical processes in fractured rock formations during a glacial advance

“…Alterations to fracture permeabilities during glacial loadings are important but these extensions are not considered in this study. The estimation of the permeability of fractures in particular is governed by the hydraulic aperture of the fracture, which can be influenced by the normal and shear stresses acting on the fracture and gouge development (Nguyen and Selvadurai, 1998;Selvadurai and Nguyen, 1999;Selvadurai and Yu, 2005;Selvadurai, 2015). Discussions of these topics and references to further studies of this important topic are given by Boulon et al (1993), Nguyen and Selvadurai (1998) and Selvadurai (2015).…”

“…Within a discrete fracture modelling approach, three distinct finite element formulations can be identified: special interface or joint elements Nguyen, 1995, 1999;Ng and Small, 1997;Nguyen and Selvadurai, 1998;Guvanasen and Chan, 2000;Steffen et al, 2014), the embedded manifold approach (Guvanasen and Chan, 2000;Juanes et al, 2002;Graf and Therrien, 2008;Erhel et al, 2009), and the conventional or direct approach, in which the fractures are modelled with the finite elements of the same spatial order; e.g. 3-D fractures are modelled with 3-D finite elements (Stanislavsky and Garven, 2003;Sykes et al, 2011).…”

Computational modelling of crack-induced permeability evolution in granite with dilatant cracks

“…The results presented do, however, clearly point to the need to account for dilatancy at the scale of microcracking in order to predict permeability evolution by means of multiscale computational techniques, as the corresponding permeability evolution confirms that the approximation of a vanishing dilatancy angle does not yield physically acceptable results. Further research could also be performed to incorporate more detailed dilatancy models as developed in [88].…”

“…It should also be noted that the experimental results show a slower permeability increase for deviatoric stresses above 250 MPa. This could likely be due to either gouge production in the cracks or due to a decrease of the dilatancy angle; fine scale modelling could be extended in future developments to account for these aspects [88,63].…”

Nonlinear mechanics of cracks subjected to indentation

“…Other nonlinear forms of interface responses are derived from consideration of conventional models of Coulomb friction, plasticity, and dilatant phenomena that account for a local-scale structure and the incorporation of damage and degradation to account for deterioration of the interface with progressive wear (Johnson 1985;Selvadurai and Yu 2005). This paper considers a treatment of the interface response that can be represented by the dilation models proposed by Plesha (1987), Selvadurai and Au (1988), and Nguyen and Selvadurai (1998). For example, by assuming that the interface is aligned with the x axis, we can show a relative displacement occurring between both sides of the interface.…”