# Double-Borehole Superimposed Effect of a New Non-Explosive Directional Rock-Breaking Method
## 4 Discussion
### Interrelationship of Double-Borehole Superimposed Effects Between Different Slotted Methods  
Because of the rock opacity, it is difficult to directly observe the rock damage process between the double holes in the in situ test; the process of crack development between the double holes can be visualized by numerical simulation. Under double-borehole loading conditions, the three rock-breaking methods, CB, SCB, and IESF, all induce superimposed stress effects in the inter-borehole rock mass. According to the results of numerical simulation, these methods also exhibit greater strain and more extensive rock damage in the inter-borehole region compared to rock masses in other orientations. In CB, the superposition area between the double holes is large due to the transmission of stress waves, so the measurement points between the double holes in the numerical simulation results all exhibited high values of compressive stress. The effect of inter-hole distance on the superposition of stresses was analyzed in detail by numerical simulation in the study by [PERSON] et al. [58], and their results showed that when the borehole spacing was 9 cm or 11 cm, the main cracks between the boreholes failed to intersect, exhibiting a vertically offset configuration. In SCB, the stress field between the double holes exhibited tensile stresses due to the slit-oriented tube, and the value of tensile stresses superimposed between the double holes was greater than that on the other side, as shown by the numerical simulation results. In SCB, the concentration of tensile stress in the energy-gathering direction, tensile stress was \(-10.89\) MPa in the inter-borehole region and \(-8.33\) MPa on the outer-borehole region. As it was shown in the double-borehole SCB simulation results by [PERSON] et al. [59], in the concentric circle monitoring points centered on the borehole, the stress generated in the direction of the axis line of the double borehole was more than 45 MPa, which was much larger than the maximum value of 16.6 MPa in the direction perpendicular to the axis line. As the monitoring points moved away from the borehole, the stress directed toward the perpendicular axis line decreased significantly, but the inter-hole region was still subjected to tensile stress, proving the superposition of the stress field between the holes. The effect of hole spacing on the superposition effect was carried out in [PERSON]'s study [60], and the simulation results showed that the superposed stress field at a spacing of 500 mm was sufficient to produce directional cracks in the rock, but when the hole spacing was increased to 600 mm, the superposed stress could not satisfy the conditions for rock damage due to the attenuation of the stress.  
In the simulation results of IESF, a stronger tensile stress field superposition effect was shown in the inter-hole region. The main reason is that the gas pressure in the fracturing process of IESF was concentrated in the surrounding rock near the boreholes, so the tensile stress formed in the slotted direction was stronger, and it showed higher superposed stress values. During fracturing by IESF, the concentration of tensile stress in the energy-gathering direction, the tensile stress in the inter-borehole region was \(-14.47\) MPa, greater than the tensile stress of \(-12.62\) MPa in the outer-borehole region. This characteristic is also due to the fact that IESF relies only on gas pressure and not on stress waves during the rock-breaking process, so it does not generate a wider range of compressive stress field as SCB does. This indicated that IESF showed stronger energy utilization in the process of directional fracturing and can realize a better directional fracturing effect.