Effects of coal seam dip angle on asymmetric load transfer paths in the overburden of inclined stopes

Objectives The coal seam dip angle is recognized as the root cause of far more complex load transfer paths in the overburden of inclined stopes compared to those of common coal seams. A clear understanding of the effects of the coal seam dip angle on the load transfer paths holds great significance for the stability control of surrounding rocks in inclined coal seams.

Methods Based on the engineering background of a certain coal mine in Xinjiang, this study investigated the asymmetric deformations and failure of the overburden in inclined stopes using physical similar material simulation experiments, finite element numerical simulations, and theoretical calculations. Furthermore, this study developed roof stress characteristic components and investigated the load transfer paths in the overburden, along with the effects of coal seam dip angle on the paths, under varying dimensions.

Results and Conclusions The results indicate that during the mining of the inclined coal seam, the transfer paths of roof stress characteristic components exhibited an M-shaped distribution along the roof inclination but a shape of double Ns along the roof strike. Meanwhile, in the direction parallel to coal seams, these components were transferred in the shape of double Vs. Consequently, the load in the overburden within the mining influence range and outside the stress boundary transferred bidirectionally toward coal walls around the stope, while that within the stress boundary transferred unidirectionally to coals on both sides along the inclination of the mining face. With an increase in the coal seam dip angle, the deflection boundary ranges of the roof stress characteristic components gradually decreased, leading to a gradually decreasing trend in the peak abutment pressure around the stope. Consequently, the roof of the inclined stope exhibited an asymmetrical fracture morphology characterized by a larger fracture extent in its middle and upper parts than its lower part. Therefore, supports in the middle and upper parts of the mining face along its inclination exhibited high working resistance with a high degree of dispersion, leading to their frequent eccentric load and no-load phenomena. Conversely, supports in the lower part of the mining face along its inclination were subjected to relatively small working resistance with a low degree of dispersion. The asymmetric transfer paths of the overburden were identified as the underlying reason for the regional distribution of the mechanical behavior of the roof in the inclined stope, with the asymmetry increasingly pronounced with an increase in the coal seam dip angle. The findings of this study can serve as a guide for the design and layout of supports in an inclined stope, serving the purposes of preventing eccentric loading and no-load phenomena, enhancing the stability of surrounding rocks, improving the mining efficiency, and ensuring the safety of coal mines.