Study on Strength Test of Coal Mass Containing Gas Based on Drop Hammer Method

After entering deep coal seam, the mechanical properties and the strength of coal and rock mass change the increase of adsorption gas quantity. In this paper, a physical test platform for the Prussian coefficient of adsorbed gas coal was built to test the firmness coefficient of coal and rock mass in different mining areas under different gas pressure conditions, so as to reflect the strength change rule of coal and rock. The results show that: with the increase of gas adsorption equilibrium pressure, the f value of coal and rock shows decreasing trend and satisfies the law of negative exponential change. The f value drops below the critical value and the outburst risk of coal changes when the adsorption equilibrium pressure of long-flame coal exceeds 0.8 MPa. Compared with tectonic coal, the influence of adsorption equilibrium pressure on f value of non-tectonic coal is more obvious. The interval of gas adsorption equilibrium pressure that has more obvious influence on the f value of various coal types: lean coal is in the interval of 0.8 MPa to 1.2 MPa, anthracite coal is in the interval of 1.2 MPa to 2 MPa, long-flame coal is in the interval of 0.4 MPa to 0.8 MPa and 1.2 MPa to 2 MPa.