Localized Failure in Brittle Rock

Failure angles predicted by Rudnicki and Rice (75) are consistent with those observed in true triaxial tests on Westerly granite (Haimson and Chang 00). Predictions incorporate a variation of inelastic consitutive parameters (sum of a friction coefficient and dilatancy factor) with mean normal stress inferred from axisymmetric compression tests. The band angle tends to decrease as the deviatoric stress state varies from axisymmetric extension to axisymmetric compression, in contrast to the Coulomb condition which predicts no variation. The predictions underestimate the observed band angles, but they capture a roughly linear increase in band angle with increasing mean stress for fixed values of the least compressive stress and a decrease with increasing values of the least compressive stress.