LAUSR

The fracture of rock mass is affected by different stress state in underground engineering. It is important to understand the crack propagation characteristics and stress distribution under different loading conditions. In this study, the FRACOD2D (the fracture propagation code) numerical modeling was conducted to analyze the propagation characteristics and stress distribution of rock-like material specimen under different loading conditions and crack geometric distribution. Crack propagation characteristics were distinct under different loading conditions, namely the tensile crack propagation under the uniaxial loading and shear crack propagation under the biaxial loading. In the uniaxial loading, the wing crack initiated at an angle of 90°, and then propagated along the maximum principal stress direction. The stress concentration occurred at the pre-existing crack tips. The coalescence of Model 1 rock bridge was caused by wing cracks and pre-existing cracks, while there was no coalescence occurred in the Model 2 or Model 3 rock bridge. Under the biaxial loading condition, shear cracks initiated at an angle of 150°, which developed from the pre-existing crack tips and propagated perpendicularly along the pre-existing cracks gradually. Moreover, secondary cracks propagated largely, whose stress concentration increased gradually with their propagation. Secondary shear cracks were interconnected, which led to the coalescence of Model 1 rock bridge The corrugated propagation of secondary cracks was observed instead of rock bridge coalescence in the Model 2 rock bridge. Pre-existing cracks of Model 3 propagated into two independent systems without cracks initiation in the rock bridge. Numerical modeling results were evidenced by laboratory tests.