Brittle fracture of rock under combined tensile and compressive loading conditions

The brittle fracture of rock with an angled crack under combined tensile and compressive loading conditions is studied using linear elastic fracture mechanics (LEFM). The modified maximum tangential stress criterion (MTSC) and the maximum shear stress criterion (MSSC) are used to check crack initiations in the tensile and shear modes, respectively. The effects of the friction coefficient of the crack surfaces and the nonsingular stresses (T stresses) on the crack initiation are studied for the cases of both low and high compressive confining pressure coefficients. The T stresses include those both parallel (T-x) and perpendicular (T-y) to the crack plane. The type of crack initiation under the combined tensile and compressive loading conditions is found to remain tensile dominated when the compressive confining pressure coefficient is small. However, shear crack extension becomes possible with the compressive confining pressure coefficient and friction coefficient increasing if the crack orientation angle is small. Moreover, the high compressive confining pressure and substantial friction are found to increase the possibility of shear crack extension. The theoretical predictions presented in this study move one step forward than the available analytical solutions for the angled crack subjected to general biaxial load and agree well with those from experimental tests.