A New Method for Predicting Double-Crack Propagation Trajectories of Brittle Rock

Multi-crack propagation is investigated mainly by experimental measurement and little by theoretical prediction. The classical fracture criteria can better predict tensile fracture under arbitrary loading conditions (pure tensile, pure shear and mixed-mode), but have difficulty in predicting shear fracture. In this paper, Mode I and Mode II SIFs of branch-cracks initiated by the original cracks were calculated by the complex function and superposition method, and a new theory of multi-crack propagation was established based on the criterion of maximum tensile-shear SIF ratio. Theoretical results of two collinear cracks under uniaxial compression show that the cracks initiate more easily at [Formula: see text] (the crack inclination angle) than other angles. Coalescence of branch-crack only occurs at [Formula: see text] with the maximum crack propagation length. Peak stress [Formula: see text] reaches minimum when [Formula: see text] (inner friction angle of rock), and the larger the [Formula: see text], the closer to the compressive strength of rock the [Formula: see text]. Mechanism of the crack initiation and propagation are all Mode I under uniaxial compression. Uniaxial compressive test results of red sandstone (the rock material is assumed to be homogeneous) pre-cracked specimens agree well with predicted results of the crack initiation, stable and unstable propagation, which can prove the validity of the new multi-crack propagation prediction method.