Rock Mech. Rock Engng. (2000) 33 (2), 75±92 Rock Mechanics and Rock Engineering : Springer-Verlag 2000 Printed in Austria Strain-dependent Fluid Flow De®ned Through Rock Mass Classi®cation Schemes By J. Liu1,2, D. Elsworth3, B. H. Brady4, and H. B. Muhlhaus1 1 CSIRO Exploration and Mining, Nedlands, Australia 2 Center for Oil and Gas Engineering, The University of Western Australia, Nedlands, Australia 3 Department of Energy and Geo-Environmental Engineering, The Pennsylvania State University, University Park, PA, U.S.A. 4 Faculty of Engineering and Mathematical Science, University of Western Australia, Nedlands, Australia Summary Strain-dependent hydraulic conductivities are uniquely de®ned by an environmental factor, representing applied normal and shear strains, combined with intrinsic material parameters representing mass and component deformation moduli, initial conductivities, and mass structure. The components representing mass moduli and structure are de®ned in terms of RQD (rock quality designation) and RMR (rock mass rating) to represent the response of a whole spectrum of rock masses, varying from highly fractured (crushed) rock to intact rock. These two empirical parameters determine the hydraulic response of a fractured medium to the induced-deformations. The constitutive relations are veri®ed against available published data and applied to study one-dimensional, strain-dependent ¯uid ¯ow. Analytical results indicate that both normal and shear strains exert a signi®cant in¯uence on the processes of ¯uid ¯ow and that the magnitude of this in¯uence is regulated by the values of RQD and RMR. 1. Introduction A knowledge of changes in hydraulic conductivity that result from the redistribu- tion of stresses or strains around engineered structures is crucially important. Changes in hydraulic conductivity, as a result of thermoporomechanical coupl- ing in a radioactive waste repository, may impact the spread of aqueous and colloidal contaminants (Pusch, 1989; Smelser et al., 1984; Skoczylas and Henry, 1995). Changes in hydraulic conductivity due to underground excavation may a¨ect groundwater in¯ows into tunnels, create di½cult tunnelling conditions and slow the advance rate (Zhang and Franklin, 1993; Wei et al., 1995; Jakubick and Franz, 1993). Changes in hydraulic conductivity due to the redistribution of stresses within coal seams a¨ect the di¨usion and ¯ow of methane, thus in¯uenc-