## 4 Borehole Resistivity Monitoring of Overburden
### Analysis of Monitoring Results  
#### 4.3.1 Analysis of Single-Borehole Resistivity Results  
Borehole #1 is located in the protective coal pillar of the auxiliary transportation roadway, which is not in the same section as borehole #2 and borehole #3, so only a single-borehole resistivity inversion can be carried out. To understand the location of resistivity change and the development height of the water-flowing fracture zone, the apparent resistivity change map is pasted onto the geological section map. As shown in Figure 8, the resistivity values are mainly concentrated at 200-300 \(\Omega\)-m, and the whole section is distributed in this resistivity range. Therefore, the apparent resistivity profile can be used as the background value for analysis, which can be used for comparative analysis of subsequent detection results. Figure 9a shows the resistivity characteristics during the initial stage of mining. At this time, the working face does not enter the control level range of the borehole. Within the range of 0-80 m above the overburden, due to the influence of advanced abutment pressure, the resistivity of local strata decreases and increases within the range of 80-100 m. With the advance of the working face, the mining position gradually enters the control range of the borehole, as shown in Figure 9b, and the resistivity value of the local area of borehole #1 at a vertical height of approximately 100 m continues to increase, which is caused by the abutment pressure that occurs during coal seam mining. As shown in Figure 9c, the resistivity increases significantly in a range of 90-110 m in the horizontal direction and 80-105 m for the vertical height of borehole #1, and the resistivity reaches 800 \(\Omega\)-m, showing that the coal seam is affected by mining disturbance and that the fractured zone has begun to develop. As shown in Figure 9d, most of the horizontal control range of borehole #1 is in the goat, and the resistivity value continues to increase in the area with a horizontal direction of 90-110 m and vertical height of 40-105 m, reaching 1200 \(\Omega\)-m, showing that fractures have developed widely in this area, which is the fractured zone, and the rest of the area is the mining stress-affected area. As shown in Figure 9e, at this time, the mining position of the working face has reached the orifice, its resistivity value continues to increase, and the fractures continue to develop, but they may still undergo dynamic change. Figure 8: Borehole #1’s resistivity background imaging profile. As shown in Figure 10a, the control range of borehole #1 is within the influence range of the goat, in which the resistivity value increases significantly between the horizontal direction of 80-110 m and the vertical height of 50-106 m, and the resistivity value reaches 1400 \(\Omega\)-m. As shown in Figure 10b, at this time, the working face is 79.5 m across the orifice, and the resistivity value of borehole #1 is relatively different near the vertical height of 106 m, reaching 1600 \(\Omega\)-m. At this height, the fractures are well developed. As shown in Figure 10c, the stopping position of the working face is 120 m across the orifice, and the resistivity change in borehole #1 tends to be stable below the vertical height of 106 m and the vertical height of 106 m. The working face is 18.3 m away from the orifice, and the working face is 18.3 m away from the orifice. forms an obvious interface with other areas. The resistivity value is 5-6 times different from the background value. The height is the development height of the fractured zone. In summary, because borehole #1 is in the protective coal pillar, its resistivity value changes slowly in the early stage of coal seam mining. After the mining position passes through the borehole, the resistivity value of borehole #1 changes drastically, and the fracture is fully developed. At the same time, Figures 6-8 show that the change in resistivity has an increasing downward influence, and a vertical height of 106 m is the characteristic interface of resistivity.