## 5 Engineering Application
### Fracturing Effect Validation  
Microseismic monitoring was conducted in the hydraulic fracturing process. Fifteen geophones installed in adjacent tunnels recorded microseismic events during fracturing, enabling the mapping of fracture geometry and spatial distribution, as shown in Figure 16. The YTZ3 high-precision microseismic monitoring system was adopted, which can monitor microseismic events with energy greater than 100 J and a frequency range of 1-1000 Hz. The sampling frequency is 1 KHz. Figure 16a shows that microseismic events were concentrated near the fracturing borehole, with scattered activity in other areas. The events followed the fracturing segments but exhibited localized clustering, likely influenced by weaker strata or segment spacing. Figure 16b reveals that fractures mainly extended along the minimum principal stress direction but deviated partially, likely due to \"stress shadow\" effects causing uneven propagation. Fracture radii were about 35 m, consistent with numerical simulations.  
Due to potential errors in microseismic monitoring, transient electromagnetic detection was also performed to validate the hydraulic fracturing range. The YCSZ drilling transient electromagnetic instrument was used, which can be pushed to a depth of 300 m with the help of a drill pipe. During detection, a transmitting coil and probe were inserted into the borehole to conduct point-by-point three-component measurements. The vertical  
Figure 16: Location results of microseismic events near the borehole. (**a**) Along the borehole axial direction; (**b**) along the cross-section of the borehole.  
component (Z) of the secondary field identified low-resistivity anomalies around the borehole, while horizontal components (X, Y) determined their spatial orientation. This created a cylindrical detection zone centered on the borehole. As shown in Figure 17, post-fracturing resistivity decreased significantly. Comparing post-fracturing data with pre-fracturing background values revealed a clear resistivity anomaly distribution (Figure 17b). In some segments, resistivity decreased by up to 60 \(\Omega\)m, with block-like patterns suggesting fracture connectivity. Segments 10-12 showed contiguous low-resistivity zones, suggesting weaker strata or overlapping fractures due to spacing variations.  
Additionally, mine pressure was analyzed. Figure 18 presents supporting resistance and stress in a coal seam of the fractured and non-fractured zones. The red dashed box represents the fractured zone. The supporting resistance in the fractured zone ranged from 326 to 417 bar, with an average of 376.4 bar. In contrast, the supporting resistance in the non-fractured zone ranged from 463 to 544 bar, averaging 502.7 bar. The supporting resistance in the fractured zone decreased by 25.10% compared to the non-fractured zone, confirming significant pressure relief. The coal seam stress also decreased, as shown in Figure 19. The average stress in the non-fractured zone was 6.5 MPa, whereas in the fractured zone it was reduced to 5.5 MPa. A decrease in peak stress indicates a reduction in stress concentration. The fractured zone shows smoother stress change curves, indicating more uniform and periodic rock failure. This is beneficial for mining planning and management.  
Figure 17: Resistivity changes before and after fracturing and abnormal resistivity areas after fracturing. (**a**) Resistivity changes before and after fracturing; (**b**) abnormal resistivity areas after fracturing.  
Figure 18: The supporting resistance in the fractured (red dashed box) and non-fracturing areas during the mining process [39; 40].