Evaluation of Rock Fracture Toughness in the Presence of Pressurized Water at Elevated Temperatures by Means of the AE Technique : Solid-Mechanics, Strength of Materials

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Fracture toughness tests were performed on rock samples of granite, andesite, tuff and mudstone to evaluate the fracture behavior of subsurface rock materials in geothermal areas. The effects of temperature, confining pressure and water environment on rock fracture toughness were shown through experiments using pre-notched cylindrical specimens in the presence of pressurized water, ranging from 0.1 to 30 MPa at a maximum temperature of 224℃. The rock fracture toughness (K_<iAE>) was defined by the critical stress intensity factor of the crack tip region at the onset of the main crack propagation, which corresponded to an abrupt increase of ΣE_<AE>before the maximum differential pressure was reached. For granite, the value of K_<iAE> at 200℃ and 20 MPa decreased down to approximately 20% of the value observed at room temperature and atmospheric pressure. However, the K_<iAE> value of andesite was independent of high temperature and confining pressure, provided that the test environment conditions were less than 224℃ and 27.4 MPa. K_<iAE> values of tuff and mudstone were obtained as intermediate between the granite and andesite.
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