EXPERIMENTAL STUDY ON THE MECHANISM OF BLAST-INDUCED CRACK PROPAGATION UNDER DIRECTIONAL FRACTURE CONTROLLED BLASTING

The dynamic propagation behavior of blast-induced cracks in PMMA material containing preexisted oblique crack subjected to directional fracture controlled blasting with two notched boreholes was studied by using new digital laser dynamic caustics experimental system. The experimental results show that the preexisted inclined crack blocked the propagation of main cracks, while two main cracks and wing cracks coalesced eventually. The tip fields of main cracks are tension stress fields, the fracture of which is similar to fracture mode I. When the main crack propagated near to the preexisted crack, the stress field at the tip of main crack and the singular stress field at the tip of the preexisted crack superposed with each other. Strong shear stress field was formed at the preexisted crack tip, while the wing crack at the preexisted cracks expanded to the main crack with the influence of main crack. The research results can provide theoretical basis for directional fracture controlled blasting of jointed rock mass.