Experimental Study on the Influence of Roof/Floor Conditions on Pillar Burst

Coal measures in the central and western regions of Mainland China are mainly composed of weakly cemented strata. However, some coal mines in these regions are characterized by hard roof and floor formations. To investigate the effects of roof and floor conditions on pillar burst and failure behavior, uniaxial compression tests were conducted on roof-coal-floor composite specimens with different lithological configurations. The failure characteristics, acoustic emission (AE) response, energy evolution, and fragmentation size distribution were comprehensively analyzed. The results show that the strength of the roof and floor significantly affects both the overall load-bearing capacity of the composite specimens and the local failure severity of the coal section. For specimens containing mudstone roof and/or floor, the burst energy index ranged from 2.30 to 2.93, indicating weak burst propensity and progressive failure controlled by the weak mudstone section. In contrast, the sandstone-coal-sandstone (SCS) specimens exhibited the highest UCS of 34.46 MPa and a typical Class II stress-strain response, indicating high burst propensity. The postpeak AE energy release rate and ring count rate of the SCS specimens reached 7.2 × 10^-3 and 4.9 × 10^-3, respectively, and the fragmentation fractal dimension reached 2.24. These quantitative results indicate that hard roof and floor conditions enhance the overall energy storage capacity of the composite system and intensify the sudden burst failure of the coal section. The findings provide an experimental basis for understanding pillar burst mechanisms under different roof and floor geological conditions.