## 4 Borehole Resistivity Monitoring of Overburden
### Analysis of Monitoring Results
#### 4.3.2 Analysis of Cross-Borehole Resistivity Results  
Borehole #2 and borehole #3 are in the same vertical section, and cross-borehole data are used for constrained inversion. The results are shown in Figure 10. In Figure 10, 0-50 m in the horizontal direction is the protective coal pillar, and the overall change in its resistivity is small. The horizontal direction of 50-110 m is the overburden, and the overburden damage is mainly concentrated in this range. Most of the resistivity values in Figure 11a are at 100 \(\Omega\)-m, which is the variation range of the normal resistivity value of the rock mass and can be regarded as the background value.  
Figure 10: Resistivity inversion profile of the working face behind the orifice.  
Figure 11: Cross-borehole resistivity imaging profile.  
The difference in resistivity values in Figure 11b is small, indicating that the rock mass maintains relative integrity at this time. When the working face is 87.1 m away from the orifice, as shown in Figure 11c, the local regional resistivity increases between the vertical height of 20-70 m. The analysis shows that the change feature is mainly affected by the advance stress, and the advance influence distance is approximately 60 m. When the working face is 54.8 m away from the orifice, as shown in Figure 11d, the resistivity value between the vertical height of 11-20 m increases significantly, and the resistivity value reaches 800 \(\Omega\cdot\) m, showing that the rock mass in this area has been broken and has begun to collapse. When the working face is 20 m away from the orifice, as shown in Figure 11e, the rock fragmentation intensifies, and the scope of the caving zone expands further to 5-20 m, initially forming the characteristics of the caving zone. At the same time, the resistivity value increases at vertical heights of 90-100 m, indicating that fractures begin to develop. When the working face continues to be mined, the roof rock mass is increasingly affected by the mining effect, as shown in Figure 11f. The fracture development range is expanded to 50-100 m and the resistivity value reaches 1400 \(\Omega\cdot\)m.  
When the working face crosses the orifice, the change range of the resistivity value decreases gradually, as shown in Figure 11g. The resistivity value with a vertical height of 5-22 m reaches 1600 \(\Omega\cdot\)m, which indicates that the rock mass in this area is relatively broken, which is characterized by the development of the caving zone. The range of resistivity in a range of 40-60 m of vertical height continues to expand, indicating that the fractured zone has undergone further expansion. When the working face is over 79.5 m from the orifice, as shown in Figure 11h, the movement and resistivity of the roof rock stratum are basically stable. The resistivity value changes greatly compared with the background value within the range of vertical height of 40-102 m, and the resistivity value reaches 1400 \(\Omega\cdot\)m, which is 5-6 times the difference from the background value, and the analysis shows that the range is typical for fractured zone development. The resistivity of the rock strata in a range of 5-22 m vertical height is high, and the local area reaches 1900 \(\Omega\cdot\)m, which is approximately 8-9 times the background value. According to the analysis of the characteristics of resistivity change, the range is judged to be the caving zone. According to the analysis of the resistivity variation characteristics of boreholes #2 and #3, a vertical height of 102 m is the upper limit of the development height of the water-flowing fractured zone, and 22 m is the upper limit of the development height of the caving zone.