# Experimental Study on the Efficacy of Water Infusion for Underground Mining of a Coal Seam
## 5 Conclusions  
In this investigation, an experimental study on the efficacy of the water infusion method for the underground mining of a coal seam was performed. First, laboratory tests were performed on various coal samples taken from actual underground mining coalfaces to determine the coal properties. A field test was then carried out on the actual coalfaces (i.e., with and without using the water infusion method). Based on the results obtained from the experimental program, the following conclusions can be drawn:  
1. The strength properties of the coal specimens were found to be functions of the moisture content and water injection time. The optimum moisture content (22.58%) and appropriate water injection time (within 20 h) were experimentally determined from the laboratory testing program. These obtained values were then employed to evaluate the efficacy of the water infusion method for the actual coal seam;
2. The physical efficacy (i.e., less longwall face failure) of water infusion for underground mining of the coal seam could be visibly observed first at the coalfaces. In addition, the quantitative results obtained from the field indicated that smaller spalling depths and faster mining speeds were attained in the coalfaces using the water infusion technique than those without using the water infusion technique, expectedly. The mining speed of the coal seam rose to 14.4 m/month (i.e., increasing 1.8 times) compared to that of coalfaces without using water infusion, due to the smaller spalling depths (i.e., decreasing 2.8 times);
3. A linear relationship between spalling depth and mining speed was also discovered from the field test results; that is, the smaller the spalling depth, the faster the mining speed. In addition, the mining speed prediction equation was proposed for the field of underground mining construction. This proposed equation was verified and well-matched results (i.e., in both training data and validating data) of the predicted and measured data were clearly observed. However, the spalling depth and mining speed could be changed, depending on the coal seam and surrounding rock conditions, such as the natural moisture of a coal seam. Therefore, the prediction model is only applicable for coalfaces in the coal seam used in this study. It should be noted that the water infusion method will be continued in the future for other coal seams. Hence, the prediction model could be verified with upcoming data;
4. In conclusion, the greater stability and faster mining speed of the coalfaces using the water infusion technique than those without the water infusion technique, obtained from the field test, strongly reinforced the efficacy of water infusion techniques for the underground mining of a coal seam.  
[PERSON] and H.P.N. participated the test program and then participated and drafted the manuscript. [PERSON] governed the result analysis and revised the draft and submitted the final manuscript. All authors read and approved the final manuscript.  
This research received no external funding.  
This work was supportedby Hanoi University of Mining and Geology; Dong Bac corp-port company.  
The authors declare no conflict of interest.