Experimental Study of Fracture and Deformation of Rocks at High Confining Pressure and Temperature

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1. Triaxial compression test was conducted at confining pressure up to 3 GPa and temperature to 300ﾟC. It was confirmed that the fracture mechanism changes at elevated temperature when the compressive strength becomes equal to the frictional strength, from ordinary brittle fracture (low-pressure type) to a high-pressure type fracture. The high-pressure type fracture is considered to be predominant in the earth's crust, excepting in the case of very high pore pressure. Combining these experimental results with the estimation of the scale effect on the rock strength, a new model for the lithosphere strength was proposed.2. An analysis of the AE data on genesis which had been measured more precisely both in the low-and high-pressure regimes, showed that the behavior of b-value before the final fracture changes between the both types of fracture.3. From the experiments on eclogite, the high pressure embrittlement was found to be a characteristic phenomenon for the rocks which exhibit cataclastic ductile behavior.4. A process of fracture nucleation was clarified from the measurement of elastic wave velocity through many paths in a rock specimen by the aid of elastic wave tomography under confining pressure by means of a new designed friction-less piston.