Abstract:

To prevent the risk of abnormal gas emissions during tunnel excavation through unstable coal-bearing strata, this study focused on the inclined shaft section of Baoanying No.1 Tunnel in the Chengdu-Kunming Railway Expansion Project. Through on-site monitoring, numerical simulation, and engineering application, gas emission patterns, risk identification methods, and prevention technologies were investigated. The results indicate that tunnel gas originates from unstable coal seams and carbonaceous rocks within the strata, and gas emissions correlate strongly with coal/carbon content in surrounding rocks and the degree of geological fracturing. Then an integrated geophysical-geological drilling approach was employed to establish an advanced identification method for abnormal gas emissions. This method utilizes multiple indicators: unfavorable geological bodies, lithological variations, borehole gas concentrations, and emission rates. A "borehole curtain" interception technique was developed for high-efficiency gas risk prevention and control. Boreholes arranged in curtain patterns were drilled from both side chambers to intercept and extract coal-rock gas ahead of the advancing tunnel face. Field applications demonstrate that this technology reduces construction interference and increases advance rates.

Key words: unstable coal-bearing strata, tunnel construction, abnormal gas emission, control technology, advanced identification method, interception and drainage