66 / 2021-09-13 13:57:01

Dr

Coal burst,,ejection velocity,coupled model

The spontaneous ejection of coal from an excavation face has become a common occurrence in certain Australian mines. Such an event is variously referred to as a pressure burst, outburst, coal burst or pillar burst. Generally, the terms pressure burst, coal burst and pillar burst apply to ejections of coal caused by high stresses as in deeper mines, whereas the term outburst applies to an ejection caused wholly or primarily by gas pressure in the coal. This study presents a method to estimate the velocity of ejection of coal fragments when a burst occurs. The sources of energy taken into account are released strain energy, pressure energy of free gas initially contained within cleat spaces, and if pulverised coal is present the pressure energy of additional free gas resulting from desorption from coal particles as the ejected coal is accelerated to its final velocity. According to the equations governing micropore diffusion within coal particles, the expansion of free gas, and acceleration of ejected coal, the rates of change of adsorbed gas concentration, free gas pressure and coal fragment velocity are interdependent. Governing differential equations were proposed based on the initial boundary conditions taken immediately after structural failure of the coal. In a case study, a burst in a development roadway of cross section 5.5m x 3.0m approaching a vertical fault filled with pulverised coal is considered, for mining depths from 250m to 750m. The burst is taken to occur when the coal face is 3.0m, 2.0m or 1.0m from the fault. Released strain energies are determined using Salamon’s energy balance equation applied to results obtained by FLAC3D three dimensional elastoplastic analysis. Various energy sources were considered and quantified using numerical modelling and analytical approaches. This work helps to predict, for a given mine layout and geological setting, whether a coal burst would be of unacceptable intensity were it to occur.