Damage-induced permeability changes in granite: a case example at the URL in Canada

This paper concerns both in situ measurements of permeability and numerical modelling of changes in permeability induced by microcrack growth. Hydraulic experiments including pulse tests with the SEPPI probe are in progress. These tests are a part of the tunnel sealing experiment (TSX) at the 420 m level of Canada's Underground Research Laboratory, whose aim is to estimate the in situ hydraulic properties of Lac du Bonnet granite. Based on laboratory investigations, the anisotropic damage model developed by Homand et al. (Comput. Geotech. 22 (1998) 135) and recently reviewed by Shao et ar. (Int. J. Rock Mech. Min. Sci. 36 (1999) 1001) has been extended in order to account for changes in permeability induced by microcrack growth. We have implemented this extension in the three-dimensional code (FLAC(3D)). Triaxial compression tests, with permeability measurements carried out on two different granites, provide a verification of the numerical implementation with a good agreement between experiments and predictions. Comparison between in situ measurements of permeability and predictions indicates that both the results of numerical modelling and observations are globally in agreement. Finally, numerical modelling as well as the in situ measurements indicate that a depth of 50-70 cm is a good estimation of the extent of excavation disturbed zone in the TSX tunnel. (C) 2001 Elsevier Science Ltd. All rights reserved.