Elastoplastic analysis of gas drainage hole based on Tresca yield criterion

Gas drainage is one of the effective methods to reduce coal and gas outburst accidents. However, for three types of soft and unstable coal seams, the gas drainage hole will collapse easily in some degree during the hole drilling process or after gas drainage for some of time under high geo-stresses. The length of gas drainage hole is much larger than the diameter, so the elastoplastic analysis of gas drainage hole under non-uniform geo-stresses can be simplified to be a plane strain problem. The rock and coal of the collapsed area are supposed to obey the Tresca yield criterion, the conformal mapping method of complex variable functions is adopted, the inner side of the gas drainage hole is equal to the gas pressure and the stresses at the elastoplastic interface are continuous, and the equations for collapsed area, stress and displacements at the elastoplastic interface are derived. In the end, the geo-stresses and physical and mechanical parameters of coal and rock are selected. The collapsed area near the vertical drainage hole and radial stress and radial displacement distribution characteristics at elastoplastic interface are analyzed. The results may provide reference for the similar projects and studies.