Modelling of outbursts at #26 Colliery, Glace Bay, Nova Scotia. Part 2: Proposed outburst mechanism and model

The outbursts experienced at #26 Colliery originated from within sandstone river channels just above the coal seam. The outburst mechanism proposed here can be used to model the outbursts experienced at this mine quantitatively. The mechanism treats an outburst as a series of instantaneous, static events driven by tensile failures within the rock mass around a spalling cavity. Outbursts may terminate simply due to stress re-distribution caused by the changing shape of the spalling cavity; if a stable shape is achieved. Alternatively, spalling could continue indefinitely unless it is terminated by a change in geology. The two main factors affecting the occurrence of an outburst are the gas pressure and the tensile strength of the rock containing the gas. The final stable shape of the cavity, when not geologically influenced, is directly dependent on the in situ stress field. Sensitivity analyses illustrate the above influences.