Crack Propagation Law of Notch Blasting under Unidirectional Confining Pressure

The deep coal mine blasting is the combined action of the initial ground stress field and the explosion load. By using the unidirectional dynamic and static combined loading test platform and the dynamic caustic experimental system, the expansion law of the initial stress field intensity on the blasting crack is explored under the horizontal or vertical unidirectional confining pressure applied to the blasthole notch on the plexiglass plate. The test results show that the grooving of the blasthole can effectively control the distribution range of the initial stress field, promote the concentrated release of energy, and improve the directional blasting effect. At the same time, the dynamic effect of explosion and the static effect of confining pressure are dominant in the near and far areas of the blasthole, respectively. The horizontal initial stress field increases the stress concentration at the crack tip and promotes the growth of the main crack. With the increase of the stress field, the promotion effect is more obvious, and the occurrence of secondary cracks is inhibited. In contrast, the vertical initial stress field reduces the stress concentration at the notch tip, inhibits the crack propagation, and transforms the crack from type Ⅰ fracture to type Ⅰ-Ⅱ mixed fracture. With the increase of stress field, the shear fracture is more obvious, and the crack propagates along the direction of the maximum principal stress.