Failure modes of the surface venthole casing during longwall coal extraction: A case study

Abstract: The effective control of gas emissions from longwall faces and gob areas in the coal mining industry in China has become increasingly important. Drilling underground gas drainage holes from a surface is an effective way to release gas. Once a coal seam is extracted, the rock strata above a gob subside and move, after which the gas drainage borehole and casing become damaged due to state changes in the rock. In this paper, we perform a deformation and failure analysis of a surface venthole casing using the numerical simulation method. The numerical investigation is carried out on the casing under compression, tension, and shear conditions. The general factors that affect casing failure are discussed, and basic failure modes are summarized. The experimental casing of the surface venthole at Cheng Zhuang Colliery (CZC) is also analyzed by numerical simulation. The actual deformation and failure of the casing are examined using on-site monitoring data, to which the numerical simulation results are then compared. We deduce that the tensile and shear failures occur at the lower part of the casing or at the bedding plane separation. Monitoring must be focused on these areas, and protective measures should be used. The numerical simulation model is simplified given various restrictions. The integration of numerical simulation and monitoring technology can serve as an efficient method for the quantitative analysis of failure on surface venthole casings. The research concepts presented in this paper and the rules deduced are useful references. [Copyright &y& Elsevier]