The main factors affecting the outburst hazard of a coal formation are rock pressure, gas pore pressure, and coal strength. Sudden outburst of coal and gas starts with the formation of an outburst cavity mouth by destroying and squeezing a formation section 0.1–0.3 m thick, with an effective radius around 0.5 m, located in the plane of the coalface bottom, to the excavation. The process is initiated by rock and gas pressure, but is hindered by the strength of the coal. For the current outburst hazard forecast, all these parameters must be kept under control. Earlier studies have shown that the rock pressure can be evaluated in accordance with the noise spectrum of operating equipment registered at a short distance from its source. Today, a regulatory standard method «based on parameters of artificial acoustic signal» is used to do that. Since the sound caused by an operating equipment unit is spread within the solid massif frame, the value of the gas pore pressure does not affect the signal spectrum and, consequently, the outburst hazard index.
Continuous measurement of gas pressure in a formation during mining operations is labor-intensive and time-consuming. This parameter, however, can be evaluated indirectly based on the methane concentration in the mining excavation atmosphere with gas control devices. Coal strength can be promptly measured by a strength metering device such as P-1 on a regular basis. The combination of these three control methods is a spectrum-acoustic method of outburst hazard forecast. The critical value of the outburst hazard index is continuously calculated based on the methane concentration and coal strength data. The degree of outburst hazard is evaluated on the basis of the ratio of the current hazard index value measured by the «based on parameters of artificial acoustic signal» method to the calculated critical value.
When performing a numerical experiment within the framework of the study, it has been shown that with the increase in methane concentration registered in the excavation atmosphere adjacent to the coalface in the course of coal cutting, the critical value of the outburst hazard index decreases, whereas it increases with the increase of coal strength.
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