Modelling of outbursts at #26 Colliery, Glace Bay, Nova Scotia. Part 3: Comparison of model results and field data

The outburst mechanism and model proposed in Part 2 of this paper has been used to simulate the outbursts at #26 Colliery. The cavities generated by the model were compatible with the actual outburst cavities in both size and shape. The model was also used to explain the presence of different size cross-sections within the same cavity; they are a result of the changing width of the sandstone exposed above the heading. The narrower the exposed sandstone, the smaller is the resulting cavity. In addition, the model shows that if an outburst is not terminated by a change in the excavation shape, it could spall indefinitely unless terminated by variations in the geology.

A siltstone bed often occurs between the sandstone channel and the coal seam. If the sandstone is not penetrated, then the overlying siltstone must fail prior to initiation of spalling (outbursting) from the sandstone. This siltstone failure has been analysed as a ‘cutter roof’ failure of a beam loaded by the gas pressure at the sandstone/siltstone interface. Results from this analysis are also compatible with the field observations.

Remedial measures should be taken when mining near an area prone to outbursts. Several potential remedial measures are discussed in the light of the model results. Further evaluation of these potential remedial measures is needed by means of on-site testing. However, the prime concern regarding the previous practice is that the entry support immediately behind the face was passive; it is thought that the installation of an active support as close to the face as possible would be a benefit.