Abstract:

To explore the mechanism of extension and coalescence of the defect (flaw) in rocks under complex stress state, the study simulated the cracking process of rock-like material containing double pre-existing flaws in the biaxial compression test based on 3D discrete element software (PFC3D) and the improved parallel-bond model (IPBM). The microscopic parameters of the numerical model were calibrated by matching both macroscopic mechanical properties (uniaxial compressive strength, tensile strength, and elastic modulus) and cracking pattern with the laboratory experiments. The results show that: the first cracks are tensile cracks which vary with the inclination angle of flaw，and the secondary cracks are shear; the confining stress will suppress the first cracks and promote the development of the secondary cracks; the coalescence patterns of samples are closely related to the geometries of the flaw and the confining stress. Two new shear coalescence patterns (New1 and New2) can be observed at the confining stress σ_c > 0 MPa. The number of microcracks in the numerical sample is greatly affected by the confining stress, but not by the flaw geometries. The initial stress and peak stress of crack are correlated with confining stress and flaw inclination angle, but not with bridging length and bridging angle. The crack extension is closely related to the stress distribution in the sample, and the cracks first occur in the stress concentration area around the pre-existing flaws. The study provides a reliable reference for the subsequent calibration of discrete element model parameters and the crack extension mechanism based on discrete element.

Key words: rock-like material, crack extension, three-dimensional discrete elements, numerical simulation, biaxial compression