## 6 Conclusions  
This study employed numerical simulations to analyze fracture propagation under varying pumping rates, compressive strengths, in situ stress differences, and segment length conditions. The impact of these parameters on the extent of fracture expansion was examined. Additionally, field experiments were conducted on segmented hydraulic fracturing in underground coal mine directional boreholes. Transient electromagnetic and microseismic techniques were used to assess the fracture extent. Monitoring data, including resistivity differences, microseismic events, and mine pressure changes of fractured and unfractured zones, were collected. Based on the monitoring results, the spatiotemporal characteristics of fracture propagation were analyzed. Finally, the effectiveness of segmented hydraulic fracturing in weakening hard coal seam roofs and improving mine pressure distribution was evaluated. The key findings are as follows:  
1. During the process of increasing the segment spacing from 12 m to 40 m, the fracture length decreased by 12%, limiting the overall fracture propagation. However, excessively small segment length can cause fractures to be influenced by the induced stress of adjacent clusters, leading to asymmetric propagation. Therefore, segment length should be optimized based on the specific objectives of the fracturing operation. Considering economic factors and fracture length, this study recommends a segment spacing of 30 m for the field application.
2. During the progressive increase of pumping rate from 5 to 40 m\({}^{3}\)/h, a 98% extension in fracture length was observed. However, underground space constraints impose limitations on equipment capacity, including flow rate and pump pressure. Thus, fracturing designs should be tailored to the characteristics of the working face, segment length, and flow parameters. Based on the results of numerical simulations, a pumping rate of 40 m\({}^{3}\)/h is recommended for the field application.
3. Segmented hydraulic fracturing in underground directional boreholes exhibits significant responses in resistivity, microseismic activity, and mine pressure variations. The experimental results indicate that this technique effectively weakens hard coal seam roofs and improves mine pressure distribution, facilitating coal mine production planning and management.
4. The numerical simulation framework developed in this study is flexible and adaptable. By adjusting key geological parameters, it can be extended to assess hydraulic fracturing performance under varying geological conditions.  
Figure 19: Stress of the fractured and non-fracturing area [39].  
**Author Contributions:** Conceptualization, M.Y.; methodology, X.W.; software, Y.M.; validation, Y.M.; formal analysis, M.Y.; investigation, M.Y.; resources, S.L.; data curation, X.W.; writing--original draft preparation, Y.M. and M.Y.; writing--review and editing, S.W. and J.H.; visualization, M.Y.; supervision, S.L.; project administration, J.H. and S.L.; funding acquisition, M.Y. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was financially supported by the National Natural Science Foundation of China (No. 52104118), and Project No. 2024 CDJXY025 supported by the Fundamental Research Funds for the Central Universities.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.  
**Conflicts of Interest:** Author [PERSON] was employed by the company Geotechnical Survey Company, CHN Energy Shendong Coal Group. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.