Modeling the stress-strain diagram for brittle rock loaded in compression

The sliding crack model introduced by Nemat-Nasser and modified by Kemeny and Cook is combined with the USR criterion of fracture to model the stress-strain diagram of brittle rocks loaded in compression. To date, the sliding crack model has been based on the stress intensity factor formulation and the fracture criterion of linear elastic fracture mechanics. The LEFM formulation is tensile-stress based and therefore it ignores the constraining effect of the finite compressive strength. The model introduced here still uses LEFM, but only to map out the stress field at the crack tip. The LEFM fracture law is replaced with the multiaxial USR criterion; which includes both the maximum and the minimum principal stress. The analytical solution for the stress-strain diagram is compared with compressive test data for Lac du Bonnet granite. The solution has the right form to capture the process of stable fracture propagation provided the deformation is produced through elasticity and axial crack propagation. (C) 1998 Elsevier Science Ltd. All rights reserved.