Abstract: At present, CH4 is replaced by CO2 in physical simulation test of coal and gas outburst, which causes a large deviation of the results. In order to ensure the similarity of simulation test while avoiding the risk of CH4, a concept of similar gas which is close to CH4 is put forward in the physical simulation experiment. Based on the mechanism of gas in outburst and similarity criterion, several similarity indices including gas content, initial velocity of gas emission, initial gas expansion energy, mechanical properties of coal containing gas are presented by combination with the coal and gas outburst prevention provisions. The mixture of CO2 and N2 is used as the original similar gas, CO2 volume fraction of which are 20%, 40%, 60% and 80%. According to the relevant specifications, the similarity indices of CH4 and the similar gases are measured respectively. The mixed gases, whose volume fraction of CO2 are 60%, 35%, 45% and 54% respectively, are similar to CH4 in the gas content, the initial velocity of gas emission, the initial gas expansion energy, the mechanical properties of coal containing gas. Correlation analysis results show that the four mixed gases are highly relational to CH4, and can be used as undetermined gases of similar gas. Simulation tests on the undetermined gases and CH4 are carried out. It is found that the phenomenon and the critical value of mixed gas with a CO2 volume fraction of 45% are the closest to those of CH4.

Key words: coal and gas outburst, physical modelling, methane, binary-component gas