Scale Effect on Uniaxial Compressive Properties of the Outburst-Prone Coal

Coal is a naturally discontinuous, heterogeneous, and anisotropic brittle material. The uniaxial compressive strength of coals is significantly affected by the sample size-dominated microstructure of minerals and fractures. The scale effect of the mechanical properties of coal is a bridge connecting the mechanical parameters of laboratory-scale coal samples and engineering-scale coal. The scale effect of coal strength is of great significance in explaining the fracturing law of the coal seam and reveal the mechanism of coal and gas outburst disaster. The uniaxial compressive strength of outburst-prone coal samples with different scale sizes was tested, the variation law of uniaxial compressive strength with increasing scale was analyzed, and the mathematical models of both were constructed. The results show that the average compressive strength and elastic modulus of outburst coal decrease exponentially with the increase in scale size, and the decrease rate is reduced. The average compressive strength of the tested coal samples decreased from 10.4 MPa for size 60 × 30 × 30 mm³ to 1.9 MPa for scale 200 × 100 × 100 mm³, which decreases by 81.4%.