Stress corrosion index is one of the important parameters to express subcritical crack growth within the rock. The mechanism of stress corrosion is influenced by the chemical effect of water in the rock and the surrounding environment. There are some laboratory tests to estimate stress corrosion index such as the double torsion test, the uniaxial compression test under various strain/stress loading rates, the uniaxial compression test and disc test under various water vapor pressures. However,

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... ince the conditions such as geometry and state of stress of the specimen and the surrounding environment are different in each test, it is likely that the stress corrosion indexes from these tests could be different. In this paper, we compared stress corrosion indexes of Kumamoto andesite obtained by three types of laboratory test. The tests included the uniaxial compression test and the disc test under various water vapor pressures, and double torsion test under a constant surrounding environment. The stress corrosion indexes were estimated to be 44 in the uniaxial compression test, 43 in the disc test and 37 in the double torsion test. These values were considered to be similar, though the value in the double torsion test was slightly smaller than the others. Furthermore, both stress corrosion indexes of another Kumamoto andesite obtained by the uniaxial compression tests under various water vapor pressures and various strain loading rates were the same values. Therefore, it is considered that a stress corrosion index is not affected by the experimental method and experimental environment very much and could be one of the material constants of the rock.