Research On Construction Ventilation Technology Of Zhegushan High Gas Tunnel

With the continuous improvement of the transportation infrastructure in the central and western regions of China,various complicated geological conditions threaten the safety of tunnel construction.Because tunnel construction is carried out in a closed environment,the consequences of an accident are serious.Through statistical analysis of tunnel construction accidents in recent years,it can be known that gas explosion accidents account for a small proportion of tunnel construction accidents,but explosions cause great loss of personnel and property.This paper takes the new zhegushan tunnel as the engineering support,and uses numerical simulation methods to study the gas distribution law of the construction ventilation of the gas tunnel and the optimization of the ventilation scheme.The main research conclusions are as follows:(1)In combination with the actual conditions of the zhegushan tunnel,a numerical model is established to analyze and study the advantages and disadvantages of the two ventilation schemes.Combined with the numerical simulation and on-site monitoring data,it can be known that the gas ventilation effect of the tunnel ventilation scheme after modification is improved.the tunnel ventilation scheme can meet the construction safety requirements of the tunnel after the occurrence of gas.(2)It is found from the numerical simulation that gas gushing from the heading face of one side does not cause pollution to the heading face of the other side and its vicinity;the gas is easy to accumulate on the side of the cross passage and jet fan.In the actual project,the monitoring of the area should be strengthened;the local duct arrangement on the heading face affects the distribution of gas mainly near heading face.When the distance from the heading face exceeds a certain value,the gas concertation distribution in the tunnel is uniform.The difference in working conditions is not great.(3)The discharge efficiency of the gas is the best as the jet fan is arranged in the upwind flow direction of 5m at the distance of the cross passage.The gas is easily accumulated in the lower part of the tunnel as the jet fan placed in a lower position,otherwise,the gas is easy to accumulate in the upper part of the tunnel.Therefore,the gas is discharged along the upper space of the tunnel when the jet fan arranged in a higher place,which is beneficial to the safety of the workers in the tunnel.The distance between air duct and heading face should not be too close or too far,the difference of air velocity on both sides of heading face is too large caused by close distance.The jet is unable to reach the heading face and the eddy is formed so that the gas at the face could not be mixed with the fresh air.When the wind pipe is at a certain distance from the heading face,increasing the wind speed at the outlet of the air duct can speed up the discharge of gas.The overall wind velocity distribution is more uniform when axial flow fan duct is arranged in the high position.The gas is easy to accumulate at the top of the tunnel due to its smaller density so that the air duct in the high position is beneficial to the discharge of gas and accumulation.