1991 Volume 107 Issue 9 Pages 593-599
The knowledge of the mechanical properties of rock under hydrothermal conditions is required to develop design methodology for nuclear waste repository and hot dry rock geothermal reservoir. In this study, in order to investigate time-dependent fracture property of Inada granite in hydrothermal environment, uniaxial compression tests have been conducted in 10 MPa water of 200°C under various constant strain rates ranging from 10-3 to 10-8s-1. Furthermore the similar tests have been carried out both in 10 MPa water of room temperature and in dry condition of room temperature to investigate the effects of the environmental factors on the rock fracture property. The results have shown that the strength decreased significantly due to water and temperature. In water, the strength decreased with decreasing strain rate and became almost constant at slow strain rates below a critical value; 10-6s-1 for 200°C and 10-7s-1 for room temperature. The main mechanism that caused the strength reduction with decreasing strain rate was clarified to be stress corrosion cracking of microcracks, which was experimentally confirmed by examining another possible mechanisms such as dilatancy hardening and mineral dissolution in hot water. The phenomenon that the influence of strain rate on the strength disappeared at very slow strain rate was theoretically discussed by developing Costin's Microcrack Model from the view point of the mechanics of microcrack growth. The discussion has shown that the lower limit of compressive strength was related to the threshold value of the stress intensity factor KISCC in stress corrosion cracking, and that the strain rate at which the strength became almost constant was related to both KISCC and the crack velocity at KISCC.
