The role of coal strength in coal and gas outbursts

Coal strength is one of essential factor influencing the occurrence of coal and gas outbursts (CGOs). In order to explore the laws of CGOs, simulation tests with different coal strengths were carried out under a self-developed CGO device. The results show that as the coal strength increases, the relative outburst strength decreases. When the coal strength increases from 0.24 to 0.5 and 1.21 MPa, the relative outburst strength decreases by 10.3% and 34.3%, respectively. The transport velocity of coal powder near the outburst hole shows fluctuating characteristics, initially decreasing and then increasing. When the coal strength increases from 0.24 to 0.5 and 1.21 MPa, the respective migration velocities of coal powder near the outburst hole are 22.45, 16.36, and 18.0 m/s. As the coal strength increases, the interval between the initial drops in gas pressure detected by each gas pressure sensor gradually increases. When the coal strength is 0.24 MPa, the outburst of coal powder particles of diameter below 0.28 mm in the outburst section is relatively large. However, when the coal strength is 0.5 and 1.21 MPa, after the 6 m outburst section, larger coal particles of diameter beyond 1 mm in the corresponding outburst section increases significantly. The greater the coal strength, the lower the degree of fragmentation of the remaining coal within the outburst cavity, and the pulverization and failure characteristics of the coal become less pronounced. Furthermore, considering the impact of gas pressure on the crushing force of coal, the equation for the tensile strength failure of outburst coal has been improved. The research results will provide scientific foundation for the design and construction of outburst prevention measures in coal seam mining.