A new mechanistic model for prediction of instantaneous coal outbursts — Dedicated to the memory of Prof. Daniel D. Joseph

An instantaneous coal outburst is a sudden and violent simultaneous ejection of large amounts of coal and gas (methane, carbon dioxide) from the working coalface during underground mining. The occurrence of such an outburst usually leads to a gas explosion and pollution of the mine. Despite extensive research efforts in the past 150 years, the physical mechanisms causing coal outbursts are still poorly understood. Here we present a new model combining fracture mechanics, gas dynamics and rock mechanics to elucidate the physical mechanisms leading to instantaneous outbursts. This model suggests a domino effect that leads to a catastrophic failure of the coal and an instantaneous outburst. The model identifies a critical condition for the onset of instantaneous outbursts, and it successfully predicts all of the observed phenomena preceding outbursts, most of which are explained for the first time. The model also predicts a fracture aperture size effect which is confirmed by the existing observation-based fracture classification scheme used to assess outburst proneness. ► Underground coal mining creates a highly fractured zone ahead of the working coalface. ► Gas flow through the fractured zone can induce an unbounded pressure gradient. ► Unbounded gas pressure gradient causes a catastrophic failure of the coal in a domino fashion and instantaneous coal outburst. ► Highly compressible flow produces audible noise and temperature drop preceding coal outburst.