Abstract: At present, the main methods for predicting outburst in China are mainly based on gas dynamic phenomena and the so-called four-parameter method (e.g. gas pressure of coal seam, failure mode of coal mass, hardiness coefficient of coal mass, and initial diffusion velocity of gas). The four-parameter method requires that coal seam should be confirmed as outburst seam only if all of the four parameters exceed their alternative critical values, and the critical value of gas pressure is 0.74 MPa. However, practices show that outbursts had happened even though the gas pressures were less than 0.74 MPa. In this paper, the outburst mechanism was overviewed by compressible fluid mechanics, and a new predicting index F was established by using the stress analysis method of multi-phase continuum mechanics. In addition, calculation method for determining the related parameters was also given. Case studies reveal that the formula accords well with the practice.

Key words: coal and gas outburst, outburst prediction, index, gas pressure, internal friction angle