Influence of surrounding environments and strain rates on the strength of rocks subjected to uniaxial compression

Uniaxial compression tests were performed under various non-atmospheric environments and constant strain rates on Kumamoto andesite. The environments considered were water vapor, organic vapor such as methanol, ethanol and acetone, and inorganic gas such as argon, nitrogen and oxygen. The strength of rock increased in the order of water vapor, methanol, ethanol and acetone vapor, and the stress corrosion index changed with changing environment even for the same rock type. The stress corrosion index was evaluated to be 31 in consideration of the water vapor pressure and strain rate. The stress corrosion index in this research showed good agreement with other researchers’ results and it can be concluded that the stress corrosion index is one of the constants representing the mechanical properties of the rock. However, it is an environment-dependent factor and may vary owing to the difference of hydroxyl ion concentrations that may exist in the same rock. Finally, it was shown that the time to failure is delayed by decreasing water vapor pressure in the surrounding environment, and then the long-term strength of rock under water vapor pressure can be estimated, based on sub-critical crack growth due to stress corrosion.