Simulation Study On The Scheme Of Smoke Extraction And Personnel Evacuation In A City Highway Tunnel

With the development of social productivity,the advancement of science and technology,and the adjustment of the industrial structure,the urbanization process in China has been accelerated unprecedentedly.Urbanization stimulates the widespread use of underground space,promotes the rapid development of urban underground rapid traffic,and effectively alleviates the problem of urban traffic congestion.Highway tunnel is an important part of the modern urban underground transportation system,due to the characteristics of airtight space,long and narrow structure,and heavy traffic,once a fire occurs in the tunnel,it will make the tunnel temporarily closed for maintenance,while it will cause the structure collapse and mass casualties.Therefore,it is of great practical significance to study the flow characteristics of tunnel fire smoke,analyze the effect of mechanical smoke control under the influence of multiple factors,and propose the targeted schemes of smoke control and personnel evacuation.This paper adopts the combination method of data investigation,numerical simulation and theoretical analysis,based on a 4.5km urban underground expressway tunnel project,to conduct in-depth analysis and research on smoke diffusion and control,personnel evacuation and other related issues aimed at a longitudinal ventilation tunnel fire.The research work and main research results in this paper obtained include:(1)For the numerical simulation of fire ventilation and smoke flow of the entire(extra)long tunnels,there are problems that the calculation is not easy to converge and it is difficult to obtain accurate calculation results,some researchers have suggested that it may be considered to be divided into multiple smoke-exhausting sections,focusing on the section where the fire is located,that is,using the "small length calculation model" for simulation calculations.When establishing a small-length calculation model,the interceptive position must be reasonably determined and the boundary conditions of the interceptive interface must be set correctly,otherwise the calculation results will be inaccurate.The method proposed in the current literature is to first conduct a "cold state simulation" of the entire tunnel,that is,the ventilation system is operative and set according to the fire conditions but not set the fire source,to obtain the air volume of each section along the tunnel.Then,a section containing the fire location is intercepted,and the smoke flow simulation of the fire conditions is performed.The boundary conditions of the interceptive section are taken according to the cold simulation results.With this method,two key issues need to be resolved: First,the air volume at a certain distance from the fire point obtained from the cold state simulation of the entire tunnel should be close to the air volume in the event of a fire,that is,in cold simulation,certain measures should be considered to "equivalent" the effect of fire on air volume;The second is the distance from the interceptive position to the fire point,which should not affect the calculation of smoke flow during the simulation of fire conditions.To discuss how to establish a small length calculation model for such tunnels in fire simulation,reference to the supporting project,a straight horizontal longitudinal ventilation tunnel was constructed,discussed how to solve the above two problems,and obtained regression models of minimum intercept length values at different longitudinal wind speeds.(2)On the basis of(1),taking the smoke exhaust sectionⅠbased on the project as an example,with the goal of personnel safety and "reasonable protection",considering the unfavorable case scenario of a fire occurs in the central position of the section,the effects of different mechanical smoke control schemes on its effect under multiple factors were analyzed,and proposed the optimal mechanical smoke control schemes in different situations.(3)For(2),based on the temperature,visibility distribution and available safe evacuation time(ASET)in the tunnel after the stabilization,the effects of the two modes on the mechanical smoke control effect of the case where the jet fan and the axial-flow fan in the shaft are in interlocked synchronous start and non-chain asynchronous start were studied,and an optimal combination of start timing was obtained.(4)Considering the most unfavorable situation of the traffic jam all the way and the fire point is directly opposite an escape staircase in the center of section Ⅰ,through evacuation simulation calculations,the relative sizes of ASET and required safe evacuation time(RSET)were analyzed contrastively.It also focused on the evacuation characteristics of personnel,the design parameters of escape stairs,and the personnel pass rate.Finally,the combination scheme of evacuation facility design was obtained.