Characteristics and differential analysis of energy evolutin of deep tectonic coal during fracturing processes

The stability and failure modes of tectonic coal under disturbance differ significantly from those of original coal. To investigate the energy evolution characteristics and disparities during the fracturing process of deep tectonic coal, the mesoscopic parameters, macroscopic mechanical properties, energy distribution of tectonic coal and microseismic characteristics in tectonic coal-bearing strata were analyzed through various loading paths combined with acoustic emission monitoring, computed tomography (CT scan) reconstruction and microseismic monitoring. The result shows distinct microstructural differences exist between tectonic and origin coal, manifested as poor surface regularity, abundant debris accumulation and stepped fractures in tectonic coal. These microstructural characteristics lead to divergent macroscopic mechanical behaviors, with linear correlations between mesoscopic and macroscopic parameters. Tectonic coal exhibits substantially different characteristic stress stages under loading when compared to origin coal, showing shorter elastic phases and stable crack propagation periods. While primary fractures induce varying degradation intensities, similar crack development patterns emerge beyond critical stress thresholds. Tectonic coal demonstrates more dispersed fracturing patterns with greater susceptibility to cyclic loading effects. Regardless of loading paths, tectonic coal tends to develop large-scale cracks with more disordered spatial distributions. Shear-dominated failures with tortuous crack paths prevail in tectonic coal, requiring higher energy consumption. The elastic energy dissipation ratio decreases during cyclic loading-unloading processes in fractured coal, accompanied by increased proportions of released energy and maximum strength reduction. Microseismic monitoring shows fewer low-energy events in primary coal zones when compared to tectonic coal areas. Tectonic coal-bearing strata exhibit higher microseismic frequency with gradual energy release patterns, while origin coal strata demonstrate more sudden seismic events, particularly requiring attention in fractured coal zones. The findings interpret field microseismic data and help early warning systems development for tectonic coal-bearing strata hazards.