封圧下における岩石のき裂進展抵抗曲線

Abstract

According to the core-based methods proposed by the authors, fracture toughness testing under confining pressure was carried out for Inada granite and Ogino tuff by using SR and C-RCT specimens, and K-resistance curves of the rocks were measured under confining pressure up to 29.4 MPa. The surfaces of a chevron-notch were sealed with a flexible and tough bellows-shaped film of copper and vinylchloride and other surfaces with a film of vinyl-chloride. In the C-RCT specimen, a fracture propagated parallel to the weakest plane (the bedding plane for the tuff and the rift plane for the granite) while, in the SR specimen, a fracture propagated perpendicular to the weakest plane to evaluate the anisotropy in the Kresistance curve under confining pressure.For both of the rocks, the K-resistance increased remarkably with confining pressure and the increase rate of the K-resistance with crack extension also became greater with confining pressure. Furthermore, the difference in the K-resistance between the two directions became greater with confining pressure. These phenomena were explained by the effects of confining pressure on the formation of process zone ahead of the crack tip. These effects are to reduce the tensile stress ahead of the crack tip by the component perpendicular to the crack plane, to decrease the rate of stress intensity factor with respect to crack extension by the same component of the confining pressure and to close pre-existing microcracks by the components parallel to the crack plane.