Influence of humidity and rock fabric on subcritical crack growth in rock

The influences of relative humidity and rock fabric on subcritical crack growth in rock have been investigated on samples of Kumamoto andesite, Berea sandstone and Shirahama sandstone. Stress intensity factor and crack velocity were measured using the double-torsion technique, and all experiments were conducted in moist air at constant temperature. Our results show that crack velocity increased dramatically with increasing relative humidity. A three-to five-fold increase in relative humidity resulted in increases in crack velocity of between one and five orders of magnitude for Kumamoto andesite and Berea sandstone, and between nine and ten orders of magnitude for Shirahama sandstone. Such increases are much larger than those predicted by classical stress corrosion theory. The increase of the crack velocity was larger for rock which contained larger amount of clays. We conclude that subcritical crack growth in rock is affected remarkably by relative humidity and the amount of clays.