Mechanical behavior and acoustic emission differences of composite coal-rock specimens with different stiffness ratios under uniaxial compression
LU Zhiguo1, 2*
(1. CCTEG Coal Mining Research Institute, Beijing 100013, China; 2. State Key Laboratory of Intelligent Coal Mining and Strata Control, Beijing 100013, China)
Abstract：Coal pillar instability arises from the interaction between the coal seam and the surrounding roof and floor strata. The stiffness ratio of the roof/floor to the coal seam directly influences the failure mode of the coal seam; thus, the roof, floor and coal seam should be studied as an integrated system. To investigate the effect of the stiffness ratio on the mechanical behavior of coal-rock combined specimens, uniaxial compression experiments were conducted on specimens with varying stiffness ratios. The deformation and failure behaviors during loading were quantitatively characterized based on the elastic modulus and failure intensity. Utilizing acoustic emission technology, the micro-fracture mechanisms and their evolutionary characteristics in combined specimens with different stiffness ratios were analyzed. The controlling mechanism of the stiffness ratio on the deformation and failure of these specimens is revealed from the perspective of micro-crack development and propagation. The research findings are as follows: (1) Variations in the stiffness ratio of composite specimens have minimal impact on the uniaxial compressive strength of the specimens, the strain of the coal samples, or pre-peak acoustic emission (AE) characteristic parameters (e.g., average ringing count, duration, amplitude, and energy). (2) The influence of stiffness ratio on the elastic modulus of composite specimens arises from differences in pre-peak deformation of the rock component. As the stiffness ratio increases, rock strain decreases, leading to reduced axial deformation of the composite specimens and an increase in their elastic modulus. (3) As the stiffness ratio of composite specimens decreases, the average particle size of failed coal samples diminishes while the fractal dimension increases, indicating an intensified degree of coal fragmentation with a decreasing stiffness ratio. (4) A decrease in the stiffness ratio of composite specimens results in a higher post-peak AE event rate, more severe signal blockage in acquisition channels, increased waveform overlap of AE events, and a higher proportion of high-amplitude and high-energy AE signals. Concurrently, the AE b-value and RA value decrease, indicating an increase in large-scale fractures. (5) The failure intensity of coal samples in composite specimens exhibits a negative correlation with the stiffness ratio. From the perspective of macroscopic energy storage and dissipation, a lower stiffness ratio leads to greater pre-peak axial deformation of the rock, allowing it to store more elastic strain energy. At peak strength, the elastic energy released by rock rebound does work on the coal sample, exacerbating coal failure. From the perspective of micro-fracture development and propagation, a decreasing stiffness ratio increases the proportion of large-scale fractures, which break the coal sample into smaller units and enhance coal fragmentation within the composite specimen. Additionally, the AF/RA ratio increases and becomes more concentrated, indicating a higher proportion of tensile fractures. Reduced energy dissipation during the failure process increases the residual energy available for conversion into kinetic energy, thereby intensifying failure.
卢志国1，2*. 单轴压缩下不同刚度比煤岩组合试样力学行为及声发射差异[J]. 岩石力学与工程学报, 2026, 45(6): 1740-1756.
LU Zhiguo1, 2*. Mechanical behavior and acoustic emission differences of composite coal-rock specimens with different stiffness ratios under uniaxial compression. , 2026, 45(6): 1740-1756.
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2026, Vol. 45 
