# Dynamic Monitoring of the Water Flowing Fractured Zone during the Mining Process under a River
## 4 Results and Discussion
### TEM Survey Results  
The field experiment was carried out before the longwall face reached the riverbed. Some of the results are shown in Figures 7 and 8. The curves of the induced electromotive forces with a slow decay indicate that a good conductor exists in this area, and the resistivity in this area is low (Figure 7). A poor conductor would result in a fast decay. Furthermore, the late time-induced electromotive force derived from a good conductor would be higher than that derived from a poor conductor (areas bordered in red in Figure 8). In other words, the resistivity of the water-bearing area is much lower than that of the area without water. As the distance of the advanced influence should be 12.2 m when the longwall face reached the riverbed, the experimental survey was carried out when the longwall face reached 1245.5 m on January 27 th. The distance between the longwall face and the riverbed was 24.5 m on that day. The survey lasted from January 28 th to February 9 th, with 90 survey points each day and 13 days in total. Because we encountered a snowstorm during the survey process on February 7 th, only 30 survey points were measured on that day. The total number of survey points is 1110. The 8101 longwall face position during the survey period is shown in Table 3. The footage of the working face is 1251.5 m on the first day of the survey, and the distance between the survey area and the working face is 18.5 m. Although there might be a fractured zone ahead of the working face, the fracture could not reach the overlying aquifer. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Weighting** & \multirow{2}{*}{**Scope**} & \multicolumn{2}{c}{**Fracture**} & \multirow{2}{*}{**Notes**} \\ \cline{3-4} \cline{6-6}  & **Distance** & & **Width** & **Depth** \\ \hline
1 & 40.5 m & \(-\)44.8 m +29.3 m & 50–60 cm & 7–8 m & First Weighting \\
1 & 17.3 m & +11.9 m & 30 cm & 2.5 m & \\
2 & 15.7 m & +14.0 m & 18 cm & 1.7 m & Periodic Weighting \\
3 & 16.8 m & +12.0 m & 20 cm & 2.0 m & The average distance of the advanced influence: \\
4 & 17.7 m & +14.1 m & 15 cm & 1.8 m & \\
5 & 14.7 m & +16.1 m & 10 cm & 1.0 m & 14.1 m \\
6 & 15.1 m & +14.3 m & 12 cm & 1.0 m & The average width of the fractures: \\
7 & 15.4 m & +15.8 m & 16 cm & 1.3 m & 17.5 cm \\
8 & 15.3 m & +14.6 m & 19 cm & 1.8 m & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The development of surface cracks after the first weighting and periodic weighting. Figure 7: Comparison of the different field experiment results. The horizontal axis represents time, and the vertical axis represents the induced voltage; both are logarithmic. The different colored lines refer to the curves of induced electromotive forces derived from the different survey stations. Figure 9 shows the TEM results without mining influence. The low resistivity area at a depth of 20-40 m corresponds to the K\({}_{\text{l2h}}\) unconfined aquifer in the lower series of the Cretaceous and the middle Jurassic coarse sandstone aquifer. The water level and volume of the aquifer remained unchanged without mining influence. Figure 10 shows the results of the TEM survey during the mining process. Combining the survey results and the position of the 8101 longwall face, the change of the water level and the development of the WFFZ during the mining process can be analyzed. The survey results of line 1 are shown in Figure 10a. The footage of the longwall face on the first day of the survey was 1251.5 m, and the survey area was not affected by mining. The arrow indicates the location of the K\({}_{\text{l2h}}\) unconfined aquifer (apparent resistivity 15 \(\Omega\cdot\)m and below, at a depth of approximately 20-40 m). The water level was stable. Affected by mining, the water from the overlying aquifer began to flow down (to 60 m and below) by the second day.