大断面公路隧道绝对瓦斯涌出量测定位置优化OA

[Objective]Since 2021,47 tunnel gas accidents have been reported in China,resulting in over 160 deaths.Gas disasters are among the major hazards in highway tunnel construction in western China,posing a serious threat to construction safety.The absolute gas emission rate is an important indicator for determining the type of gas formation or gas work area in highway tunnels,influencing project investment,construction efficiency,equipment selection,safety measures,and management systems.However,the method for measuring the absolute gas emission rate of highway tunnels provided in the Technical Specification for Design and Construction of Highway Gas Tunnels(JTG/T 3374-2020)relies on empirical values,and the gas concentration is taken as the maximum value,which may result in considerable discrepancies between the calculated results and the actual situation.In addition,the wind speed measurement points in the return air section are subdivided into multiple grids,resulting in many measurement points.Under the working conditions of large-section highway tunnels,accurately measuring wind speed at these points is challenging,resulting in inaccurate calculations of absolute gas emissions.[Methods]Based on the Huangjiagou Tunnel of the T3 section expansion project on the Chongqing Zunyi section of the Lanzhou Haikou National Expressway,Fluent software was used to numerically simulate the gas behavior in the tunnel.The left-side tunnel was excavated for 200 m,encountering coal seams for research.The air duct outlet was 10 m from the tunnel face,with a 2 m diameter,and its center was 5 m above the ground.The outlet was located at the arch waist on the right side of the tunnel,adjacent to the inner wall.The model was constructed according to the actual tunnel dimensions and appropriately simplified to analyze the distribution laws of the airflow and gas concentration fields in the large-section highway tunnel.The measurement position for absolute gas emissions in the highway tunnel was optimized.MATLAB software was used to fit the wind speed and gas concentration at a section 120 m away from the tunnel face.Onsite testing was conducted to verify the numerical simulation results,which showed good agreement with theoretical values.[Results]The flow law of gas in the tunnel under ventilation conditions was analyzed through numerical simulations,and the effects of different gas emission rates and ventilation air volumes on the determination of absolute gas emission rates were analyzed.By selecting a section at a suitable distance from the palm surface for wind speed and gas concentration measurements,the number of measurement points can be reduced to six,decreasing onsite labor intensity and considerably improving the accuracy of gas emission measurements.[Conclusions]Based on the actual working conditions of the tunnel,a section 120 m from the tunnel entrance was selected for the measurement of absolute gas emissions.The number of absolute gas emission measurement points can be reduced from 26 to 6,and the correction coefficient K of the absolute gas emission calculation formula is 7.9.Five different absolute gas emission conditions were simulated at the same air volume,and the calculated values had errors of less than 8%compared with the theoretical values,indicating good accuracy.