Analysis of the influence of coal thickness on the physical and mechanical characteristics of coal and rock mass

In order to study the influence of coal thickness on the physical and mechanical characteristics of coal and rock mass, the samples of coarse grained sandstone, coal, as well as coal and rock mass in Bultai Coal Mine were taken as the research objects. The uniaxial compressive strength, elastic modulus and peak strain were studied by RMT-150C mechanical testing machine. The results show that the coal thickness has a significant effect on the density and wave velocity of coal and rock mass, with the increase of the coal thickness, the density and wave velocity of coal and rock mass decrease gradually; the coal thickness has little effect on the uniaxial compressive strength of coal and rock mass, but has significant effect on its peak strain and elastic modulus. Compared with coarse grained sandstone, when the coal thickness in coal and rock mass are 5 mm, 10 mm, 15 mm and 20 mm, the peak strain increases by 2.2%, 20.7%, 25.3% and 38.3% respectively, the peak strain increases with the increase of the coal thickness in the coal and rock mass; the elastic modulus is reduced by 30.5%, 41.5%, 48.2% and 51.8% respectively, the elastic modulus decreases with the increase of coal thickness in coal and rock mass.The research results are helpful to further reveal the internal reasons of the phenomenon such as roadway support difficulties, rock pressure appears violently, and surface step subsidence and so on.