Effects of coal properties on ventilation air leakage into methane gas drainage boreholes: Application of the orthogonal design

Ventilation air leakage into underground to inseam drainage boreholes is a common issue observed during gas drainage in underground coal mines. This air leakage adversely affects the gas drainage efficiency. Despite the extensive research conducted on air-leakage prevention strategies, the effects of coal properties on the air leakage has not yet been properly investigated. This paper presents a fully-coupled numerical study on the effects of coal properties such as Young's modulus, Poisson's ratio and porosity on the air leakage into drainage boreholes. This was achieved through an integrated approach of the orthogonal design method and the F-test theory. The results show that there is a direct correlation between the Young's modulus and the amount of air leakage. Furthermore, the F-test theory was used to examine the significance of the above-mentioned properties’ effects. It is found that the impact of Young's modulus on the air leakage is the most significant among those three properties. The Poisson's ratio is the next significant factor with an inversely proportional relationship. Porosity is found to have the least effect on the air leakage. This study provides a systematic approach to examine the air leakage performance for various site conditions and coal properties. Research outcomes offer the mining researchers and engineers a guidance to develop appropriate leakage-prevention strategies and enhance gas drainage performance.