Study on gas characteristics and prevention measures of small section hydraulic tunnel in non-coal measure strata

Based on the Yunwuzhai Tunnel in the Tingzikou Irrigation District Project, this study analyzed gas characteristics in small-section hydraulic tunnels within non-coal strata through geological surveys, field tests, and laboratory experiments.Combining engineering practices, the research investigated gas prevention measures, evaluated their control effectiveness, and proposes corresponding mitigation strategies.The results showed that: Yunwuzhai Tunnel was a small section high-gas tunnel because it was located in the target area of oil and gas migration, and it was difficult to dilute the gas by ventilation because of the gas-bag gas in non-coal-measure strata through which the tunnel passes.During the construction process, it was detected that the maximum gas concentration on the face of Yunwuzhai Tunnel was 1.1%, the maximum gas concentration at the emission point was 76%, and the maximum gas concentration at the return flow was 0.293 5%.The subsequent construction might encounter high concentration gas emission.The gas accumulation in small section tunnels of non-coal measure strata could be effectively diluted by using the dual fan ventilation mode of "mixed type + push type".Quantitative analysis results showed that the gas concentration of the face and the return flow was highly negatively correlated with the wind speed.