Deciphering confining pressure effects on coal failure mechanisms using acoustic emission approaches

With the gradual transfer of coal resource mining to the deep part, the high confining pressure (CP) environment in which the coal is located puts forward higher safety and security demands on its mechanical properties and failure behavior. To reveal the deformation and failure mechanism of coal under CP and its acoustic emission (AE) evolution pattern, this study carries out compression experiments of coal samples under different CPs and combines with AE technology to monitor the crack propagation process in real time. The key to this study lies in the systematic integration of AE multi-parameter analysis and statistical fractal methods to quantitatively reveal the crack propagation mechanism of coal under varying CPs. The results showed that the increase of CP significantly enhanced the peak strength and deformation capacity of coal samples. Moreover, the strain energy analysis showed that the high CP helped to enhance the elastic energy percentage of coal and reduce the intensity of dissipative energy release. As for AE parameters, the b-value decreased with the increasing CP; while the S-value slightly increased. Meanwhile, AE energy followed a power-law trait, while the critical index declined as CP rose, reflecting a higher likelihood of large-energy events under elevated CP conditions. The AE signal also followed Hurst’s statistical law, and the increase in CP strengthened this statistical pattern with a higher Hurst’s exponent. The AE energy fractal results further revealed that the AE energy sequence exhibited stronger scale aggregation and regularity under high CP conditions. This study systematically reveals the mechanism of the influence of CP to the dynamic response and multiscale rupture characteristics of coal, which provides a theoretical basis for the prevention and control of coal-rock hazards under deep mining conditions.