Study on Rock Breaking Effect of Double-hole Delay Blasting in Interbedding Base on Particle Expansion Loading Algorithm

By researching the distance between the interface of the soft-hard rock strata and blasthole, as well as the delayed initiation time, the rock blasting effect can be more controllable. Firstly, the rationality of the blasting method was verified from three angles: the blasting coupled stress field, the ratio of the crushing area radius to the blasthole radius, and the crack network state. Under the condition of soft-hard rock strata, the numerical model of double-hole blasting was established by using PFC 2D . Then delay blasting experiments were carried out under different positions between the structural plane and the blasthole, and the analysis was made from three perspectives: crack network, crack quantity and rock fragments. Results show that: (i) When detonated in hard rock, if the distance between structural plane and blasthole is greater than twice crushing area radius, the closer structural plane is to the blasthole, the more obvious the "hook" phenomenon between the two blastholes is. With the increase of delayed initiation time, "hook" phenomenon will weaken or even disappear. (ii) Based on the crack information initiated in hard rock, the law of the crack number varying with the thickness of hard rock and delay time is obtained. (iii) For initiation in hard rock, the extension range of crack is large, but less fragments are formed. The law is opposite to that initiation in structural plane and soft rock. The fragmentation increases exponentially with the increase of soft rock thickness, and the exponential function is obtained.