# Dynamic Monitoring of the Water Flowing Fractured Zone during the Mining Process under a River
## 1 Introduction  
The hydrogeological conditions of coal mines in China are quite complex, and water-bearing bodies exist in coal mines. Water inrush accidents not only cause a huge number of casualties and economic losses but also seriously affect the normal production of the coal mine. Water inrush accidents occur mostly as roof water inrush during extraction. In general, the fractured roof strata can be divided into the caved zone, fractured zone and bending zone. The water flowing fractured zone (WFFZ) is composed of the lower two zones, in which mining-induced fractures are relatively developed. The connection between the mining-induced fractures of the longwall face and the overlying water-bearing bodies results in a strong water-conducting channel, through which the water from the overlying aquifer flows downward into the longwall face and causes a water inrush accident. Consequently, it is necessary to determine the developmental mechanisms of a WFFZ and the water flow mechanisms during the mining process to guide the safe extraction of a longwall face.  
Many scholars have studied the developmental mechanism and height prediction of WFFZs. An empirical formula was developed through both theoretical and practical research involving several hundred longwall faces in the development of a WFFZ of overlying rock strata after mining [1, 2], providing a theoretical basis for the fast calculation of the height of a WFFZ. [PERSON] et al. [3] studied the key stratum of the overlying strata and found the effects that the key stratum has on the development height of the WFFZ. [PERSON] et al. [4] detected the height of the WFFZ after mining using a borehole water injection (discharge) fracture measuring system and a borehole teleview logging system. These measures turned out to be intuitive and precise. Currently, numerical simulation and laboratory modeling are used mostly to estimate the development of the WFFZ and water inrush mechanisms [5, 6, 7, 8]. Field detection after mining is also widely used. However, no research on the measurement of the height of the WFFZ and water inrush mechanisms during the mining process has been reported. Because the transient electromagnetic (TEM) method is sensitive to low apparent resistivity areas, simple in construction and adaptable to complex geologic environments, it has been widely used to detect water enrichment areas in recent years [9, 10, 11, 12, 13]. The TEM method has been widely used due to its sensitivity to underground aquifers [14, 15, 16]. [PERSON] et al. [10] used the TEM method to detect a mined-out area and concluded that the water-filled voids were enlarging with time. [PERSON] et al. [17] detected both sides of the Araba fault using the TEM method combined with 2D forward modeling, 3D forward modeling and data processing, and then analyzed the difference in resistivity on the two sides of the Araba fault. Therefore, this paper attempts to detect the WFFZ with the TEM method.  
The present research was carried out in the Selian No. 1 coal mine. There is a river passing through the surface of the 8101 longwall face. The river is usually dry, and the main source of water is rain, which can cause a temporary flood. The mining depth in this area is approximately 125 m. The unconfined aquifer beneath the river has strong lateral recharge capacity, and the groundwater reserves in the rainy season are extremely large. Once the flood water flows down the mining-induced fractures into the longwall face, it will cause a serious accident. The objective of the present research was to monitor the developmental mechanisms of the WFFZ following the mining of the longwall face and analyze the water inrush mechanisms of the 8101 longwall face. It is hoped that the results can provide technical support for mining beneath aquifers and provide a reference for future research on groundwater resource migration and environmental protection.