Theoretical approach to dependence of crack growth mechanism on confining pressure

We calculated the stress field on and around an elliptical open crack locat ed in an elastic medium under various confining pressures. The problems wer e treated as two-dimensional ones by using complex potentials, and the cons iderable differences between uniaxial and triaxial crack growth mechanisms were recognized. A uniaxial condition allows a certain elliptical open crac k to develop by itself (without any crack-crack interactions) along its maj or semi-axis, whereas a triaxial condition does not. This is the principal mechanism of transition from uniaxial to triaxial crack growth. Our transit ion model, derived using a theoretical approach, explains the dependence of experimental results, such as crack distribution and internal friction ang le, on confining pressure well. We conclude that uniaxial and triaxial crac k growth mechanisms fundamentally differ from each other, and that attentio n must be paid to experimental conditions when applying experimental result s to phenomena in the Earth.