Criteria for brittle fracture in compression

Abstract

Fracture nucleation and propagation in the compressive stress field of the geological and the mining environment is considered with the purpose of formulating an empirical, but general fracture criterion that is in agreement with experimental evidence. Present fracture criteria are inadequate for compressive loading. The boundary stress-based theories ignore the effect of the stress gradient while the critical stress intensity concept of fracture mechanics neglects the normal stress that acts parallel with the direction of fracture propagation. A new, empirical crack resistance (CR) function is defined based on experimental data and then combined with an ‘averaged’ state of stress in front of the cracktip to formulate a ‘crack driver’ (CD) function. The crack driver is analogous to the safety factor, but with values greater than unity representing the fractured state. The crack driver concept is implemented to predict the nucleation and propagation of fracture in a compressive environment. The evolution of the failure process around underground openings is then described, with special reference to the primary, the remote and the slabbing types of fracture of rock mechanics and mining terminology.