## 2 Pre-Splitting Blasting Seam Formation Mechanism and Damage Theory
### Mechanism of the Effect of Different Detonation Time Intervals in Pre-Splitting Blasting  
The pre-stress effect of the first detonated hole on the subsequent hole in pre-splitting blasting can be categorized into three typical scenarios based on the magnitude of the detonation time interval between two adjacent holes [26], as shown in Figure 2: (a) represents detonation with a long time interval, (b) represents detonation with a short time interval, and (c) represents simultaneous detonation.  
Figure 1: Explosive gas-driven crack propagation model.  
Short-time interval detonation can effectively utilize the superposition effect of stress waves, enhancing the formation and propagation of cracks and thereby improving the effect of pre-splitting blasting. If the detonation time interval is too long, the stress fields of the two blast holes will no longer superimpose, resulting in independent detonations and a reduced overall blasting effect. The ideal pre-splitting blasting effect, where a through crack is formed along the line connecting the centers of two holes without leaving radial cracks on the half-wall hole traces, is only possible under the (b) detonation condition shown in Figure 2 (detonation with a short time interval).  
During the simultaneous detonation of two blast holes, the stress waves between the holes interfere with each other, leading to random crack generation. Despite the superposition of stress waves, crack formation primarily propagates from the hole wall rather than from the center of stress superposition. This indicates that simultaneous detonation is not the optimal condition for achieving the penetration of cracks between blast holes. In the case of delayed detonation, the stress wave generated by the first detonated hole will affect the crack propagation of the subsequently detonated hole. Specifically, when the subsequent hole detonates, the longitudinal wave generated by the explosion of the first hole creates a favorable tensile stress field around it, promoting crack propagation. During delayed detonation, the speed of crack propagation increases, and with appropriate delay, cracks can more effectively penetrate between blast holes. The speed of crack propagation significantly increases after the interaction between the stress wave and the crack, indicating that the influence of the stress wave is crucial for crack propagation. To overcome the randomness of crack generation around the first detonated hole, a guiding hole can be drilled next to it, and an appropriate detonation time interval can be adopted. This can effectively control the generation and propagation of cracks, thereby improving the effect of pre-splitting blasting. During blasting, the empty holes near the charged hole act as stress concentrators, as shown in Figure 3, directing cracks towards the nearer empty holes. The perforations near the charged hole guide the cracks and inhibit their propagation in other directions. When uncoupled charging is used, the charged hole also exhibits the properties of an empty hole. Sequential pre-splitting blasting is initiated as the delay time increases, from the smallest to the largest. Thus, the subsequently detonated holes can be considered to act as empty guiding holes for the first detonated holes. Therefore, in practical applications, the key to optimizing the effect of pre-splitting blasting lies in the rational design of detonation time intervals and blast hole arrangement.  
Figure 2: There are three typical time differences in the initiation between blast hole A and blast hole B. (**a**) detonation with a long time interval; (**b**) detonation with a short time interval; (**c**) simultaneous detonation.