An experimental investigation of hydraulic behaviour of fractures and joints in granitic rock

A method of measuring mean mechanical aperture of fractures based on gas vo lume balance is introduced. The effects of shear displacement and normal st ress on mechanical and hydraulic behaviour of fractures are also investigat ed. The results obtained from tests conducted on granite samples from Olymp ic Dam (Central Australia) are compared with those calculated from existing shear dilation theories. It is Found that hydraulic aperture is considerab ly narrower than the measured mean mechanical aperture. This highlights the need to consider tortuosity and surface roughness of fractures in the calc ulation of hydraulic aperture. It is also found that shear dilation angle d ecreases linearly with increases in confining pressure, as opposed to more rapid decreases predicted by existing empirical models. From the results of this study, a range of data describing the relationships between confining pressure, shear displacements, hydraulic aperture and permeability are pre sented, which could help to develop stimulation programs for geothermal res ervoirs. (C) 2000 Elsevier Science Ltd. All rights reserved.