Analysis of shear dilation and permeability of a hydraulic fracture in granite

Two-dimensional height distributions were measured along matched paths for the upper and lower surfaces of a hydraulic fracture created in the laboratory for granite. An analysis on dilatant behaviors and the permeability of the fracture during shear under small normal stress and during closure after being sheared was performed by using the height distributions of the surfaces and by solving Reynolds equation with a finite difference method. The results showed that remarkable shear dilation occurring under small normal stress results from the decrease in the degree of correlation between the two fracture surfaces and is governed by components with a few largest wavelengths, and that the hydraulic aperture normalized by the mean aperture of a sheared fracture is much greater than that of a fracture without being sheared when they are closed to have the same mean aperture normalized by the initial standard deviation of the aperture.