Background The spatial distribution of stress in coals in underground coal mines is a significant factor influencing the safe production of mines and the optimization of mining processes. The quantitative, advanced prediction of in-situ stress in coals is significant for the precise regulation of the underground stress field and the classification of areas with rock burst risks.
Methods Using the self-developed monitoring-while-drilling system, this study conducted indoor coal drilling experiments under different drilling conditions and explored the laws of effects of drilling conditions on drilling parameters (e.g., torque and drilling displacement) under varying stresses. Furthermore, this study developed a method for determining coal stress based on drilling parameters and verified this method through the in-situ engineering application in an underground coal mine.
Results and Conclusions The results indicate that the monitoring-while-drilling system could monitor the drilling parameters in real time in the presence of disturbance to the drilling process. In the drilling process, the drilling rate negatively correlated with the weight on bit (WOB) but positively correlated with the torque. The functional relationship between the drilling indices and the stress in coals exhibited a high goodness of fit (R2 = 0.92). The in-situ engineering application revealed that the differences between the stress in coals predicted based on drilling parameters and the actual stress were less than 10%, suggesting relatively high consistency. This study demonstrates that it is reliable to determine the stress in coals based on drilling parameters and also provides a scientific reference for the development of in-situ digital drilling technology for determining stress in coals.
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