Influence of Coal-Rock Height Ratio on the Mechanical Properties and Crack Evolution Patterns of Combined Coal-Rock Bodies

Abstract

The proportion of coal and rock in the coal-rock composite determines the overall deformation instability of the structure. To clarify the relationship between the mechanical behavior, the crack evolution characteristics of the combined coal-rock body, and the rock-coal height ratio, scanning electron microscopy, uniaxial compression, and acoustic emission (AE) tests were conducted on composites with different rock-coal height ratios. The mechanism of the coal-to-rock height ratio's influence on the mechanical behavior and crack evolution of the composite is expounded in detail. The findings indicate that an increase in the rock ratio enhances the peak strength and elastic modulus of the combined body, inhibits pre-peak rupture, and reduces the peak strain of the composite; as the proportion of rock height increases, the failure mode of the composite shifts from splitting to shear and ultimately to tensile failure. The extent of damage before the peak is reduced, and the deformation during the post-peak phase exhibits an initial rise followed by a subsequent decline. During the process of uniaxial compression, both the stress at which cracks begin to form and the stress at which damage occurs in the coal-rock composite increase linearly as the rock height ratio improves. This suggests that an increase in the rock proportion effectively reduces the formation of cracks in the combined body. The research findings can offer an academic foundation for the green mining of deep coal and the recovery mining of residual coal.