Effect of confining pressure on fracture toughness of Indiana limestone

The use of linear elastic fracture mechanics for modeling the fracture of rock is discussed and compared to Griffith theory. Fracture toughness, KIc, is measured for single-edge-notch specimens of Indiana limestone as a function of hydrostatic pressure. Results of 11 tests are reported for which specimens were pre-cracked in fatigue, jacketed with urethane, and loaded to failure under superimposed confining pressure. KIc is found to increase from 0.93 MN m−32 (0.85 ksi √in.) at atmospheric pressure to 4.2 MN m−32 (3.8 ksi √in.) at a confining pressure of 62 MPa (9000 psi).