Abstract
Initial distribution of microcracks in Inada granite is examined by microscopic observation of thin sections cut in three directions perpendicular to each other. The result shows that the distribution of microcracks is very imhomogeneous in spatial distribution. Namely, though the average of grain size is about 2 mm, main forming minerals such as quartz, feldspar and biotite are dispersedly distributed, so that they make clusters which distance are about 5 to 10 mm and independent of the cutting direction. Therefore the microcracks is also dispersedly distributed because most of microcracks are observed in quartz grains. This distribution of microcracks must affect on the mechanical and hydraulic properties of this rock.
The frequency distributions such as crack orientation and crack length are calculated by image analysis of microcracks which lengths are longer than 0.1 mm. The distribution of crack orientation corresponds with the orientation of three splitting planes which are observed in the quarry of Inada granite except that the orientation of grain plane in the quarry is different by 10 to 20 degrees from the orientation of mode in crack orientation. In view of orientation of crack distribution, this granite is not perfectly orthotropic material. This property plays an important role of ultimate fracturing of the specimen under triaxial compression particularly when the specimen is loaded in the direction vertical to the rift plane. On the other hand, the frequency distributions of crack lengths are almost the same in shape in spite of the cutting direction.
