Research On Key Technology Of Spiral Tunnel Construction Ventilation

With the gradual deepening of the “One Belt,One Road” strategy,the construction of highways and railways in China has ushered in new development opportunities,More and more comflex forms of tunnel engineering have emerged,and new challenges have been put forward to the construction ventilation technology of tunnels.Based on the JinJiaZhuang extra-long tunnel,this paper combines theoretical anlysis,numerical simulation and field test to analyze the relevant parameters of spiral tunnel construction ventilation and the design of tunnel multi-face construction ventilation scheme.The main research results of this paper are as follws:(1)The three-dimensional numerical model of spiral tunnel with different radius of curvature is established,and the distribution of flow field and the law of gas diffusion in the tunnel during construction ventilation are studied.The research shows that with the decrease of the radius,the asymmetry of the flow field in the tunnel becomes more obvious.The wind speed outside the tunnel is larger than the inner side of the tunnel,and the gas is also unevenlt distributed.The gas accumulation area gradually moves toward the inner arch of the tunnel.(2)Through numerical calculation,the influence of each parameter on the gas concentration in the tunnel is obtained by taking the wind speed at the end of the duct,the distance from the end of the duct to the tunnel excavation surface and the position of the duct as variables.The research shows that wind speed at the end of the duct plays a vital role in the gas concentration of the whole tunnel.As the wind speed at the end of the duct increases,the gas concentration decreases gradually,the distance from the end of the duct to the tunnel excavation surface and position of the duct have a certain influence on the gas concentration and distribution of the area near the excavation surface.In actual engineering,the duct should be arranged outside the curved tunnel,and the distance from the end of the duct to the excavation surface should be controlled at 15 m.(3)Based on the basic theory of tunnel construction ventilation,the required air volume of each excavation surface of JinJiaZhuang extra-long tunnel is calculated,and the tunnel ventilation scheme is optimized by field test and theoretical calculation.The final decision is to adopt a prees-in ventilation scheme for the import and export work area,and the inclined shaft work area adopts a more economical,applicable and convenient “Windbox Continuous” ventilation scheme.(4)A three-dimensional numerical model of the inclined shaft work area of the JinJiaZhuang extra-long tunnel was established.The optimized ventilation scheme was calculated and analyzed,the diffusion and migration law of carbon monoxide generated by the blasting was obtained.It is predicted that carbon monoxide is easy to accumulate at the intersection of the left line tunnel and the 3# vehicle cross channel.When the site is constructed,this area should be monitored and local ventilation should be strengthened.