The Study On Combined Ventilation Scheme For Urban Special Long Underwater Road Tunnel

On the one hand,because the length of the urban special long underwater road tunnel is long,the pollutant emission of the vehicle is large,which leads to a large amount of required airflow in the tunnel and the difficult pollution discharge in the tunnel.On the other hand,the pollutants discharged in the tunnel will have a serious effect on the atmosphere environment outside the tunnel since the tunnel is located in the city.Therefore,in the study of ventilation scheme,it is necessary to satisfy the environmental requirements both inside and outside the tunnel.The natural ventilation at the top of the tunnel is critical for dispersing local pollution outside the tunnel.Combined ventilation scheme with top opening and mechanical ventilation can make the tunnel ventilation more ideal.At present,there is still less research and experience accumulation for the special long road tunnel with combined ventilation scheme with top opening and mechanical ventilation at home and abroad.Therefore,based on the principles of fluid mechanics and ventilation network theory,this paper uses Fortran to compile a operation ventilation calculation program for road tunnel,and referring to a tunnel in Wuhan,a one-dimensional numerical model of the urban special long underwater road tunnel ventilation is established.The ventilation effect of the top opening combined with full jet longitudinal ventilation,only the single shaft section longitudinal ventilation scheme,the top opening combined with the single vertical shaft section longitudinal ventilation,and the influence of the related parameters on the ventilation effect of the combined schemes are studied.The results show that:(1)Under the initial design conditions,the top opening combined with the full jet scheme can not meet the ventilation requirements of the original tunnel.By changing the relevant parameters,when the top opening section is moving to about 600m-4500m from the tunnel entrance,the length of tunnel before the opening is changed to less than 4500m or the broken area of the tunnel is increased to more than 81m~2,the top opening combined with full jet can satisfy the ventilation requirements of the tunnel.(2)When the single vertical shaft subsection longitudinal ventilation scheme is adopted,the single shaft diversion scheme can not meet the ventilation requirements of the original tunnel;the single shaft feeding and discharging scheme can meet the ventilation requirements of the original tunnel,the best shaft position is 4800 meters from the tunnel entrance.At this point,78.9%of the total vehicle emission from the tunnel is discharged from the tunnel outlet,which has a serious impact on the surrounding environment of the tunnel.(3)When the top opening combined with the single shaft subsection longitudinal ventilation scheme is adopted,the top opening combined with single shaft diverted discharge scheme can not meet the ventilation requirements of the original tunnel;the top opening combined with single shaft feeding and discharging scheme can meet the ventilation requirements of the original tunnel.The best position of the shaft is to be located at the 4800meters of the tunnel entrance.At this time,the discharge rate of the shaft mouth is 12.2 percent,the discharge rate of the tunnel exit is 14.6 percent.The remaining 73.2 percent of the pollutants are dispersed by a large number of natural vent at the top of the tunnel,which greatly disperses the environment pollution outside the tunnel after the pollutants are discharged from the tunnel.