Research on risk analysis and precaution measure of coal-and- gas outburst in hydraulic tunnel

A sudden outburst of powdered coal occurred at the heading face in the No.6 middle coal seam at the inlet section of Shuidaqiao Tunnel in Guizhou Province of China. To scientifically and accurately grasp the gas outburst risk of the coal seam, the main parameters such as the composition, pressure, content, initial emission speed of gas, and the consistent coefficient of coal seam were measured through in-situ and laboratory tests. Then the single-index analysis method and the comprehensive indexes ( D and K ) analysis method were employed to scientifically determine that the No.6 middle coal seam gas shows indeed significant risk. Finally, considering the safety, economy, and time limit of the project comprehensively, an integrated outburst precaution measure of "advanced geological prediction + grouting cut-off wall + gas pre-drainage + grouting sealing + effect verification" in a segmented and multi-cycle manner was designed and implemented. The field application result indicates that the coal-and-gas outburst precaution measure above is scientific and effective, and can ensure the normal and safe construction of Shuidaqiao hydraulic tunnel. The research results can provide references for risk analysis of coal-and-gas outburst and its prevention and control in similar hydraulic tunnel passing through coal seam.