Composition characteristics of soft coal seams with large inclination angles and mining heights and the deformation of roadway surrounding rocks

The work aimed to characterize the composition properties of soft coal seams and the deformation of roadway surrounding rocks in Panzhihua Coal Mine, Guizhou, China. Experimental analysis, numerical simulation, and field tests were conducted to study the composition characteristics of soft coal seams with large inclination angles and large mining heights and their roadway deformation. Both steeply inclined thick soft coal seams and gently inclined thin soft ones share essentially identical primary mineral compositions and coal component types. Besides, pore structures were predominantly characterized by large-pore development and semi-enclosed pores. Compared to gently inclined thin soft coal seams, the steeply inclined thick soft seams exhibited lower porosity, average pore diameter (4 V/A), median pore diameter (A), and total pore volume. In contrast, they had higher bulk density, median pore diameter (V), and total pore area. The apparent density, however, showed a negligible difference between the two seam types. For the number 7 coal seam, increasing the seam inclination angle intensified stress concentration in the roadway surrounding rocks and progressively amplified asymmetric deformation. The increased roadway height-to-width ratio shifted the primary load-bearing zone away from the roadway and increased its thickness, which escalated deformation in surrounding rocks. Significant differences existed in stress distribution and rock movement around roadways intersecting different rock strata, with deformation heavily influenced by cross-stratum tunneling. Borehole observation of number 7 coal seam's 110,706 open-off cut roof determined the loosening zone of 0-8.05 m.