Effects of water on rock strength in a brittle regime

Failure strengths of granite and andesite have been measured under various conditions of strain rate and confining pressure both in the dry and wet states. Constant-stress creep tests for granitic samples have been also conducted. All specimens show that the failure strength decreased linearly as the logarithm of the strain rate decreased. The strain rate dependence of the failure strength is increased at higher confining pressures. The strain rate effect is more apparent on the failure strengths of wet samples than dry samples in lower confining pressure ranges. In the constant-stress creep experiments, the creep failure strength decreased as the logarithm of the time to failure increased. Time-dependent failure strength of all rocks observed in the regime of the present study may be interpreted by subcritical crack growth assisted by the stress corrosion mechanism.