Abstract: This paper presents an investigation into crack evolution in rocks containing pre-existing double flaw by distinct element method. Based on experimental data, a zero-thickness microscopic bond contact model containing rolling resistance is proposed and implemented into distinct element method commercial software. Crack propagation and coalescence in double-flawed rock samples under uniaxial compressive conditions are modeled. The mechanisms of crack propagation and coalescence are illustrated from the macroscopic and microscopic viewpoints. Simultaneously, the crack propagation and coalescence as well as strength properties measured in the Discrete Element Method (DEM) simulations are compared with the experimental observations. The results demonstrate that tensile stress concentrations between the pre-existing flaws and in their endpoints cause the instability and failure of rock samples containing pre-existing double flaw. The crack evolutions obtained from experiments and our DEM simulations are in good agreement. Rock samples containing flaw of an inclined ? =30°to the horizontal is most easily to initiate, while rock samples containing flaw of an inclined ? =75°to the horizontal is most difficult to initiate.

Key words: discrete element method (DEM), bond model, pre-existing flaw, crack evolution mechanism