# Double-Borehole Superimposed Effect of a New Non-Explosive Directional Rock-Breaking Method
## 5 Conclusions  
This study of the double-borehole superimposed effect of coal-based solid waste expansive agent for directional rock fragmentation resulted in the following main conclusions. 1. The instantaneous expansion with a single fracture (IESF) generates approximately \(300\) mL of high-temperature and high-pressure gases from \(1\) g of solid material within \(0.05\)-\(0.5\) s. Through the directional action of slit-oriented tubes, these high-pressure gases transform traditional three-dimensional volumetric fracturing into two-dimensional planar fractures. The gas pressure distribution law of IESF in directional cracks was analyzed and the directional fracture expansion criterion was established. 2. The stress fields of CB, SCB, and IESF were analyzed by numerical simulations. The stress distribution in CB was relatively random, and a wide range of compressive stress field was formed around the borehole. 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. The tensile stress in the inter-borehole region was \(2.56\) MPa greater than the tensile stress in the outer-borehole region. 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. Similar to SCB, there was a stress-superimposed effect between the double holes of IESF, while IESF achieved a better directional effect with less energy. 3. The strain fields of CB, SCB and IESF were analyzed by numerical simulations. In CB, the strain was concentrated at the main fractures. SCB exhibited higher strain along the energy-gathering direction, with strain values of \(7\) mm and \(8\) mm on each side, while the strain perpendicular to the shaped charge direction measured \(1.5\) mm. IESF exhibited a strain of \(6\) mm along the slotted orientation, while strains in non-slotted directions measured less than \(1\) mm. The strains generated by IESF mainly increased rapidly in the energy-focused directions, and there were almost no high-strain zones around the borehole. It indicated that IESF had a greater control ability over the energy distribution than CB as well as SCB. 4. In situ tests showed that there was a superimposed effect under double-hole loading, and the pattern was consistent with the numerical simulation results. The fracture distribution in CB was relatively random. In SCB, the main fracture was generated along the slotted orientation, while there were small secondary fractures occasionally generated in the other direction, and the damage in the inter-borehole region was greater than that in the outer-borehole region. The average crack rate of SCB was found to be \(85.0\%\), while that of IESF was \(95.5\%\). IESF achieved superior directional fracture control compared to both CB and SCB, generating only two directional fractures along the slotted orientation, and produced longer axial cracks. **Author Contributions:** Conceptualization, Q.Z. and M.H. ; methodology, Q.Z. ; software, S.G.; validation, C.W., Y.W. and S.G.; formal analysis, C.Y. ; investigation, Y.W. ; resources, R.Y. ; data curation, K.C. ; writing--original draft preparation, K.C. ; writing--review and editing, Q.Z. and C.Y. ; visualization, K.C. ; supervision, J.W. ; project administration, R.Y; funding acquisition, Q.Z. and M.H. All authors have read and agreed to the published version of the manuscript. **Funding:** This work is supported by the National Key Laboratory Fund Project of China Nuclear Uranium Industry (NKLUR-2024-YB-016), the National Natural Science Foundation of China (No. 52404155), Basic Research Program of Jiangsu (No. BK20231071), the China Postdoctoral Science Foundation (No. 2024M753523), the Jiangsu Provincial Association for Science and Technology Youth Science and Technology Talent Support Project (No.