Experimental Study on Crack Propagation of Rock by Blasting under Bidirectional Equal Confining Pressure Load

Rock blasting during tunneling has shown that the rock failure in high in situ stress environments is different from that in low in situ stress conditions or with a shallow rock mass. In particular, the propagation direction of the main crack induced by blasting is greatly affected by the in situ stresses. In order to study the law of crack propagation in rock during blasting under the conditions of an initial in situ stress, a transparent material that conformed to the mechanical properties of hard rock was used to carry out a similar model rock blasting test, under a unidirectional load. The results show that initial stress has a great influence on the propagation number, length, and direction of the main radial cracks. The specific performances were as follows: under the action of an equal confining pressure load, the longest main radial crack in the model specimen propagated along the diagonal direction, and the number and length of the main radial cracks propagated decreased with the gradual increase of confining pressure stress; in addition, the diameter of the circumferential cracks also decreased with the increase of stress, and there was a negative correlation between them. In view of the phenomenon where the longest main radial crack propagated along the diagonal direction in the model test, a mechanical model was established in this study to explain this process. This is of practical significance for understanding the mechanism of rock fracture when blasting with high in situ stresses.