| Owing to the rapid population growth,heavy traffic and scarce ground land resource have become main problems our cities are facing these days.In this context,underground interchange tunnels,a new strategy to improve the urban land use,is drawing more and more attention.This is an emerging underground transportation hub structure with good development prospects.Compared with general tunnel engineering,an interchange tunnel is a complex underground network composed of ramp tunnels and main road tunnels.It is featured with complex linear,three-dimensional intersection and plenty branches.In such a tunnel network,how to meet the safety,comfort and hygiene standards of each tunnel branch,and ensure the effective control and emission of smoke in the case of tunnel fire emergency has become a difficult problem to be solved.It is of great significance to develop a reasonable and effective interoperable tunnel operation ventilation scheme for the operation safety of interchange tunnels.On such basis,combined with the characteristics of underground tunnels,this paper comprehensively adopts the research methods of data investigation,model experiment,theoretical analysis and numerical simulation to design a hybrid ventilation system for interchange tunnels.With the research,the following main conclusions have been received1.With the method of model experiment,a calculation method to predict local resistance coefficients arisen when air flows through the bifurcations in interchange tunnels has been obtained.The results show that the local resistance coefficient is determined by following factors:split ratio,split angle,the length to height ratio and the jagged shape of the transition section.Firstly,the number of segments of the enlarged transition section was taken as fixed value,and the distribution characteristics of the local resistance coefficients based on the other three factors were studied.Then the influence of the previously fixed factor was included as modified coefficients.This finally leads to the complete calculation method.2.Based on tunnel ventilation theory,a combination between Bernoulli equation and numerical simulation was used to a theoretical study on a hybrid ventilation system.In this ventilation system,ramp tunnels and main road tunnels adopt semi-transverse and longitudinal ventilation schemes respectively.The specific results include:a)the calculation method of the static pressure distributions in air ducts and tunnels with forks;b)the fan arrangement in main road tunnels;c)the influence between the semi-transverse and longitudinal ventilation systems3.With the methods of theoretical derivation and numerical simulation,detailed design methods for key parameters of air supply and exhaust vents in the semi-transverse ventilation system was obtained.These two kinds of vents are used to supply fresh air in normal operation mode and exhaust smoke in fire situation separately.In both methods,a kind of multi-blade valve is used to take the role of the damp to control air flow.And for the first time,a theoretical method to determine the outflow by adjusting the blade opening angle of the valve installed on air duct was successfully investigated.Besides,the optimized parameters including interval and size of the exhaust vent were given in detail4.A series of fire smoke control strategies for underground interchange tunnels were researched and developed.Different fire scenes including the main road tunnel fire,the ramp tunnel fire and the fork fire were simulated with CFD software.For each kind of fire scenes,measures are the cooperation between the longitudinal ventilation systems in main road tunnels and semi-transverse ventilation system in ramp tunnels,and the simulation results have proved good efficiencies in smoke exhaustionThe research results above have been successfully adopted in Shugang-Lu’ao interchange tunnel in Xiamen city.And they should also be of great reference meaning for other interchange tunnels to be built. |
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