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.