## 4 Prevention Measures and Engineering Practice  
### Prediction of the Dangerous Area  
The SCWID is likely to happen when the key strata break simultaneously under the influence of load transfer from UCA. Therefore, it is of great significance for the prevention and control of the disasters if the dangerous area of SCWID can be predicted before mining. In this way, the dangerous area can be avoided in the mine design and mining, and some effective measures can be taken in advance to avoid possible disasters. According to the research results of the literature [28], when there is a primary key stratum in the overburden within the range of 10 times of the mining height of the coal seam, it is easy to cause the structural instability of the overlying key strata, resulting in the water inrush and support failure disasters. According to this principle, the dangerous area of water inrush can be analyzed. In literature [23], a similar method was used to judge the dangerous area of No.3\({}_{2}\) coal seam in Qidong coal mine. However, with the mining of the lower coal seam, it is also necessary to predict the dangerous areas of No.6\({}_{1}\) and No.7\({}_{1}\) coal seams. According to previous research [29], in the area of repeated mining, it is considered that because the upper coal seam mining has caused damage to the rock strata, the risk of water inrush and support crushing of working face under the goal is low. Therefore, this paper mainly studies the risk of water inrush under the initial mining condition of the lower coal seam.  
The first step is therefore the identification of the locations of the key strata [27]. Based on the overlying strata breakage rules, the identification method of the key stratum and calculation software can be used to identify the location of key strata and their structural types, thus providing the basis for prediction of dangerous areas.  
Take the identification result of three drilling holes of No.7\({}_{1}\) coal seam as examples, group A in Table 3 shows the single key stratum in No.24-257 drilling hole, the primary key stratum is only 3.42 m from 7\({}_{1}\) coal seam, which is less than 7-10 times of mining height, water flowing fracture will develop to the UCA when overlying strata breaks entirely. Therefore, it is dangerous when No.7\({}_{1}\) coal mining near this borehole. In group B of Table 3, No.Caiqian3 borehole shows multilayer key strata, which were located 53.54 m from No.7\({}_{1}\) coal seam, far more than 7-10 times of the mining height (which is about 19.32-27.6 m). Under the influence of mining, the key stratum breaks step by step from the bottom to the top of bedrock, the height of water flowing fractured zone will be less than 53.45 m and will not develop to the UCA. Therefore, there is no risk of SCWID in No.7\({}_{1}\) coal mining near this borehole. In group C of Table 3, No.296 borehole has multilayer  
Figure 10: Drilling results of water flowing fracture height in 7\({}_{1}\)14 working face.  
key strata, but the primary key stratum is only 6.82 m from No.7\({}_{1}\) coal seam, which is less than 7-10 times of mining height and the water flowing fracture will develop to the UCA. Therefore, the area near No.296 borehole is a dangerous zone of SCWID.  
Based on the methods mentioned above, the category of areas (dangerous or not) on plans of mining and designing through the analysis of key strata location and structure types. The predication result of dangerous areas of SCWID at No.7\({}_{1}\) coal seam in Qidong coal mine was shown in Figure 11. Based on the prediction results, it was found that the water inrush positions of overpressure support in No.7\({}_{1}\) coal seam are in the danger area, which shows that the prediction method and prediction result are consistent with the actual situation.