| When the tunnel passes through the gas-containing strata,accidents such as gas suffocation and explosion may occur with a little carelessness,causing casualties,huge economic losses and bad social impacts.Therefore,increased attention to the construction ventilation of gas tunnel at home and abroad in recent years.The paper relies on the Longquanshan No.1 tunnel project.Through consulting the domestic and foreign related documents,and combining with the theoretical analysis and the numerical simulation,the technology of construction ventilation for super large section tunnel in non-coal gas strata is studied.The main research results obtained in the paper are as follows:(1)Relying on the actual highway tunnel project,using Fluent computational fluid dynamics software to establish a numerical analysis model,the law of distribution and diffusion of wind flow field in the tunnel are obtained.Studies have shown that the wind flow field in the super large section tunnel is still divided into four areas,namely the impingement jet area,the adjoining jet area,the vortex area and the recirculation area,and when the wind flow approaches the vortex area,the wind velocity will drop sharply.(2)Through numerical simulation calculation,the gas distribution and diffusion law in the tunnel under ventilation conditions are obtained.Studies have shown that in the first 5s,the air flow has not reached the heading face of the tunnel in a large amount,making the gas concentration of the heading face of the tunnel rise sharply,then the gas concentration drops rapidly,and then slowly rises.After about 12 minutes,the gas concentration remained basically stable,and its value was 0.006.The area with higher gas concentration is from the lower corner to the spandrel area near the wall on the side of the heading face away from the air duct.(3)Taking the diameter of the duct,the hanging position of the duct,the distance between the duct outlet and the heading face,and the wind speed of the duct outlet as variables,numerical simulation calculations are used to obtain the wind flow field and the gas distribution and diffusion law of each factor.Studies have shown that when the air volume is constant,the air duct with a diameter of 1.4m can dilute the gas better,and the gas concentration distribution uniformity is better,but it should meet the wind pressure requirements of the fan.Considering the average gas concentration,maximum gas concentration and the uniformity of gas concentration distribution in the tunnel face,it is more reasonable to hang the air duct at the lower corner.The air outlet of the air duct is too close or too far away from the heading face to achieve better ventilation effect.When the air duct is 20 m away from the heading face,the gas can be diluted better,and the gas distribution uniformity is higher.On the basis of maintaining economic efficiency,increasing the wind speed at the air outlet of the duct,that is,using a fan with a larger air volume can effectively reduce the gas concentration.(4)Taking the diameter of the air duct,the distance between the air outlet of the air duct and the heading face and the hanging position of the air duct as variables,16 orthogonal experiments were designed using orthogonal tables,and the calculation results were analyzed by range and variance.The significant sequence of the influence of various factors on the gas concentration on the heading face and the optimal ventilation scheme for the tunnel were obtained.Provide a certain reference meaning for actual construction. |
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