Abstract
Two methods have been applied to investigate the crack behaviors of Inada granite under constant stress and cyclic stress conditions. One method is to analyze the photomicrographs of thin sections prepared from the specimen unloaded at the several loading stages under two confining pressures (0 and 25 MPa). The following results have been obtained. New cracks mainly yield in the initial stage of loading under the creep test and the fatigue test, most of which are parallel to the maximum principal stress direction. In the succeeding stage of loading, new cracks rarely yield. Instead, existing cracks propagate with elapsed time of loading frequently passing through quartz grains.
Another method is to observe directly, with the aid of CCD-camera, the surface of the specimen under uniaxial loading condition. In the fatigue test, opening and closing of the crack in accordance with the loading and unloading are confirmed. During the creep test, stable growth of the open crack toward the loading direction is identified.
