## 4 Engineering Verification  
In this study, the overburden was sampled, and its saturation was determined before grouting at the grouting working face in the Linhuan Coal Mine in Huaibei, Anhui Province, China, and the Yuan No.2 Coal Mine in Bozhou, Anhui Province, China, of Huaibei Mining Industry. The effect of the initial saturation of the overburden on the leakage of slurry-bled water into the working face was investigated. The sampling locations of rock samples at the #10 coal seam roof and floor of the 1061 longwall working face and the heading head of the mechanical link lane (the #9 coal seam floor) of the 9116 longwall working face in the Linhuan Coal Mine are shown in Figure 10. The natural moisture content and saturated water absorption rate of nine groups of specimens are respectively tested for sandstone and mudstone of #9 coal seam floor, sandstone of #10 coal seam floor, and roof. The natural moisture content and saturated water absorption of nine groups of specimens in the Yuan No.2 Coal Mine were tested, respectively, on the sandstone of the upper shaft bottom of the eighth mining area and the mudstone of the 7238 longwall working face. Figure 8: Saturation of overburden (the sites of #3, #6, #9, #12) near the upper part of working face and the results of bled water seepage monitoring for S11, S12, S14, S15 vs. time at initial saturation of 73%. (**)** #9, #12, S11, S12, S14, S15 and (**)** #3, #6. Figure 9: The planform relationship of the leakage monitoring points (S1–S18) and saturation monitoring points (#3, #6, #9, # 12) of the bottom of the overburden. The natural moisture content of rocks in their natural state can be expressed as  
\[w_{a}=\frac{m_{a}-m_{d}}{m_{d}}\times 100\% \tag{2}\]  
The saturated moisture content of rocks can be expressed as  
\[w_{sa}=\frac{m_{sa}-m_{d}}{m_{d}}\times 100\% \tag{3}\]  
The saturation of rock obtained from Equations (2) and (3) can be expressed as  
\[S=\frac{w_{a}}{w_{sa}}\times 100\% \tag{4}\]  
where \(w_{a}\) is the natural moisture content (%); \(m_{a}\) is the quality of the specimen in its natural state (g); \(m_{d}\) is the quality of the specimen after drying (g); \(w_{sa}\) is the saturated moisture content (%); \(m_{sa}\) is the quality of the specimen after forced saturation (g), and \(S\) is the saturation (%). The natural moisture content and saturated moisture content of the specimens were respectively calculated by Equations (2) and (3). The results of Linhuan Coal Mine and Yuan No.2 Coal Mine are shown in Figures 11 and 12, respectively. The saturation test results of the Linhuan mine and Yuan No.2 mine were calculated by Equation (4), as shown in Table 1. Due to the easy disintegration of the mudstone, the average values of the natural moisture content of the mudstone of the #9 coal seam floor of the Linhuan Coal Mine and the 7238 longwall working face of the Yuan No.2 Coal Mine only were measured to be 2.09% and 2.05%, respectively. The test results from the Linhuan Coal Mine show that the average saturation is 83%, 81%, and 62%, respectively; thus, it is not saturated. The test results from the Yuan No.2 Coal Mine show that the natural moisture content and saturated water absorption capacity are 4.1% and 3.6%, respectively. Considering the experimental error, the two values are considered close to each other, indicating that the sandstone is saturated in situ. From the test results, the saturation of the overburden in the Linhuan Longwall Coal Mine is low; the slurry-bled water is absorbed by the overburden, and no water is found at the working face during the grouting injection process. Since the saturation of the overburden in the Yuan No.2 Coal Mine is close to full saturation, it is difficult for the overburden to absorb the slurry-bled water completely, so the slurry-bled water appears at the working face. Figure 10: Plan view of sampling at Linhuan Coal Mine 1061 and 9116 longwall working face. Figure 11: Natural moisture content and saturated moisture content in Linhuan Coal Mine.