Influence of coal rank and tectonic stress intensity on mechanical properties of coal rock

This paper focus on systematically investigating the influence of coal rank and tectonic stress intensity on the mechanical properties of coal. 20 coal samples in different regions and different coal ranks were tested to collect the uniaxial mechanical parameters. The testing data and data from other literature were analyzed using comparative analysis, statistical regression, and significance test. The changes of uniaxial compressive strength, uniaxial Modulus of elasticity and uniaxial Poisson’s ratio under different tectonic stress zones and coal ranks were revealed and the relationship between any two of these parameters were discussed from the genetic mechanism.The results show that as the coal rank increases, the Modulus of elasticity increases. The coal rank has the effect of increasing the Modulus of elasticity of coal.In the mid-high to high stress area, the coal is prone to vertical deformation, resulting in low Modulus of elasticity, and the tectonic stress intensity has the effect of reducing the Modulus of elasticity of coal. It is also found that the nonlinear coupling between coal rank and tectonic stress intensity determines the characteristics of coal Poisson’s ratio, and the Poisson’s ratio increases with the increase of coal rank. The coal in the mid-high to high stress region is not easy to undergo lateral deformation, resulting in a relatively small Poisson’s ratio, and the tectonic stress intensity has the effect of lowering the Poisson’s ratio. In different tectonic stress areas, the Modulus of elasticity and compressive strength of coal of different coal ranks are positively correlated. However, the coal rank and tectonic stress intensity affect the speed of Modulus of elasticity with compressive strength. Furthermore, the interaction between coal rank and tectonic stress intensity affects the Poisson’s ratio-Modulus of elasticity. For the low coal rank coal, the Poisson’s ratio-Modulus of elasticity relationship is reversed from the negative correlation of the low-medium stress region to the positive correlation of the high-high stress region. For the medium rank coal, Poisson’s ratio-Modulus of elasticity relationship maintains a negative correlation from the low-medium stress region to the mid-high to high stress region. These phenomena can be reasonably explained by the microscopic deformation mechanism of the matrix pores after the vertical layering direction of different coal ranks in different tectonic stress zones.