Mechanics-Permeability Similarities Between Natural-like and Natural Coal–Rock Specimens—A Comparative Study

Investigating the mechanics-permeability similarities between natural-like and natural gas-bearing coal–rock specimens provides a theoretical basis for using natural-like specimens as substitutes for natural ones in laboratory simulations of the incubation of coal–rock gas composite dynamic disasters. Based on the similarity between coal and rock in uniaxial compressive strength ratio, natural-like coal–rock specimens were prepared; their mechanics-permeability responses were analyzed through uniaxial and triaxial tests. Both specimen types underwent brittle failure under uniaxial compression, with compressive strength falling between those of coal and rock components but closer to that of coal. Under loading axial stress (LAS), bearing capacity was directly proportional to confining stress (σ3) for both specimen types—at instability failure, both axial and radial strains increased with σ3, whereas the axial-to-radial strain ratio decreased; under unloading confining stress (UCS), both specimen types showed reductions in compressive strength and axial strain at peak strength, along with an increase in radial strain, reflecting pronounced dilatancy. Overall, the natural coal–rock specimen (NRCS) and natural-like coal–rock specimen (NLRCS) exhibited similar mechanics-permeability patterns under both uniaxial and triaxial tests, suggesting that natural-like specimens can serve as substitutes for natural ones in laboratory simulations.