抄録
A hydraulic fracture was made in the laboratory parallel to the rift plane in a block of Inada granite. Cylindrical specimens containing a part of the fracture were then taken from the block by boring the block perpendicular to the fracture surfaces. To determine the initial aperture distribution of the fracture, height distributions of the two surfaces of the fracture were measured from a common reference surface along matched linear paths of about 41mm in length with a profilometer which had a stylus tip of 0.025mm in radius. The common surface was determined by fitting one half of the specimen into the other half and holding both halves in a jig consisting of two V-blocks of steel. Spectral and statistical analyses were carried out for the roughness of the linear profiles and the initial aperture distributions of the fracture.
Main results obtained in this study are summarized as follows:
1) Many positions along the profile were measured as having a negative initial aperture. This was considered to be caused by opening of secondary cracks existing behind the main surfaces due to the release of the specimen weight. Accordingly, the initial aperture in this study was taken to be that measured when half the weight of the specimen was applied to the surfaces.
2) The roughness of the linear profile was fractal in the range of this study. The fractal dimension determined from power spectral density ranged from 1.36 to 1.48 (mean. 1.43). However, the initial aperture distribution created by the two fractal surfaces was not fractal because the power spectral density was flattened for the wave length greater than the average grain size of the granite.
3) The RMS (root mean square) of the roughness of the linear profile ranged from 0.43mm to 0.89mm (mean. 0.61mm). The mean value and the RMS of the initial aperture ranged from 0.13mm to 0.25mm (mean. 0.17mm) and from 0.12mm to 0.27mm (mean. 0.19mm), respectively.
4) The RMS of the initial aperture increased with that of the roughness of the linear profile and the mean value of the initial aperture increased with the fractal dimension of the roughness of the linear profile.
5) The frequency characteristics of the central curve of the initial aperture were almost the same as those of the roughness of the linear profile. Tortuosity, which was defined as the squared ratio of actual length of the path to the nomminal length, was estimated to be 1.25 on the average.
