A unified model with solid-fluid transition for coal and gas outburst and FEMLIP modeling

•The outburst mechanism is described by the Solid-Fluid transition of gas-bearing coal.•A unified model with the solid-fluid transition is established to describe the outburst initiation and development.•FEMLIP is adopted to solve the large deformation during the outburst process. As coal and gas outburst is a frequent disaster and its mechanism still unclear, consistent numerical modeling is indispensable to enable further investigations owing to difficulties in field observation. As gas-bearing coal with outburst proneness is considered a granular material, the outburst phenomenon is described by a solid-fluid transition that is developed in gas-bearing coal. Inter particle meso-contacts become bondless while the gas-bearing coal is sufficiently degraded. The solid-fluid transition occurs in case of the vanishing second-order work (d2w) when the gas pressure threshold (pt) is satisfied. A unified model for describing the consistent process of outburst is established herein. Finite elements method with Lagrangian integration points (FEMLIP) is used to model solid-fluid transition behavior of gas-bearing coal. The numerical results present the entire process of the outburst and satisfies a four-stage description. The unified model for outburst is beneficial for the study of the outburst mechanism.