# Double-Borehole Superimposed Effect of a New Non-Explosive Directional Rock-Breaking Method
## 4 Discussion  
### Comparison of IESF with Other Rock-Breaking Methods  
As a non-explosive directional rock-breaking method, IESF displays fundamental differences in rock-breaking mechanisms compared to CB and SCB, resulting in distinct fragmentation outcomes. In constructing the theoretical model, the effect of stress waves and blast-induced gas on the surrounding rock was taken into account in CB and SCB [45; 46; 47; 48]. In the studies of [PERSON] et al. [48] and [PERSON] et al. [49], the stress wave attenuation law and the stress field distribution around the borehole were established, respectively, and it was pointed out that the cracks would undergo expansion when the tangential tensile stress generated was greater than the tensile strength of the rock. The intensity factor of the crack tip of SCB under the action of the slit-oriented tube was given in the study of [PERSON] et al. [50], and the crack extension conditions were given. The effect of the burst-induced gas in the SCB on the intensity factor of the crack tip was considered in the study of [PERSON] et al. [51], and the corresponding propagation criterion was given. In this paper, when using IESF, the theoretical model was developed from the view that the generated high-pressure gases drove the fracture propagation. For the crack propagation criterion between the double holes, the gas pressure distribution within the crack was first determined, and this was used to derive the intensity factor at the crack tip. When it was greater than the dynamic fracture toughness of the rock, it is assumed that the crack produced an extension. In numerical simulations, the rock-breaking process demonstrated randomness in energy distribution and a highly destructive nature characterized by extensive disturbance to surrounding rock in CB. Numerical simulation results revealed randomness in crack quantity and orientation, along with a wide distribution of stress fields. Similar results have been found in others' simulations, where the use of CB in both tunnels and coal mines produced extensive damage areas around the boreholes [52; 53], demonstrating the characteristics of CB's extensive and strong disturbances. In SCB, although the slit-oriented tube can effectively protect the non-slit directions and control the energy transmission path of blast-induced gases, it only partially suppresses the propagation of stress waves. Consequently, numerical simulations revealed compressive stress fields and strain fields over a relatively large area around the borehole. This shows consistency with the results of SCBs in the studies of others, which produce some degree of damage in the non-slotted direction, both in laboratory tests and numerical simulations [54; 55]. In contrast, as a \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Borehole Number** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** \\ \hline Crack length/m & 11.3 & 11.1 & 10.7 & 11.5 & 10.5 & 10.9 & 11.1 & 11.2 & 10.8 & 11.4 \\ Length of slit-oriented tubes/m & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 \\ Crack rate/\% & 86.9 & 85.4 & 82.3 & 88.5 & 80.8 & 83.8 & 85.4 & 86.2 & 83.1 & 87.7 \\ \hline \end{tabular}
\end{table} 
Table 1: Statistics of cracks in boreholes of SCB. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Borehole Number** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** \\ \hline Crack length/m & 12.4 & 12.6 & 12.3 & 12.5 & 12.2 & 12.5 & 12.7 & 12.9 & 12.3 & 11.8 \\ Length of slit-oriented tubes/m & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 \\ Crack rate & 95.4 & 96.9 & 94.6 & 96.2 & 93.8 & 96.2 & 97.7 & 99.2 & 94.6 & 90.8 \\ \hline \end{tabular}
\end{table} 
Table 2: Statistics of cracks in boreholes of IESF. non-explosive rock-breaking method, IESF showed a completely different rock-breaking process. Unlike CB and SCB, IESF only utilizes high-pressure gas to apply loads to the surrounding rock.