| Under the implementation of the strategy of becoming a transportation power and the Belt and Road Initiative,China’s highway tunnels have been rapidly developing,and subsea immersed tube tunnels have also gradually been applied in transportation construction.With the development of ventilation technology in immersed tube tunnels,smoke exhaust is no longer solely performed through a single method after a fire occurs,but often involves the addition of longitudinal wind synergy to control and quickly remove smoke.Therefore,the smoke flow characteristics and personnel evacuation safety under the action of longitudinal wind for various smoke exhaust methods are worth studying.In this thesis,based on the structure of the subsea immersed tube tunnel of the Hong Kong-Zhuhai-Macao Bridge,a fire model was constructed,and the smoke characteristics and smoke exhaust efficiency of the top exhaust,side wall exhaust,and side wall + smoke baffle vertical exhaust smoke exhaust methods in the immersed tube tunnel after the addition of longitudinal wind speed were studied.By combining environmental control standards for personnel safety evacuation with changes in temperature,CO concentration,and visibility at eye level,different safe evacuation times were determined for side wall,side wall + baffle,and top exhaust smoke exhaust in the immersed tube tunnel under different longitudinal wind speeds.The necessary safe evacuation time is calculated by simulation and theoretical calculation methods,and compared with each other.The differences are analyzed and the evacuation safety of personnel under different conditions is evaluated.The characteristics of personnel evacuation in a free evacuation immersed tube tunnel were studied by investigating data on the exercise characteristics of different age groups and establishing a free evacuation model,and optimization proposals were put forward.The main conclusions of the study are as follows:(1)When there is no longitudinal ventilation,side wall smoke exhaust has the best vertical control of smoke,with the minimum smoke layer thickness,and top exhaust has the best vertical control of smoke,while side wall + baffle smoke exhaust has the worst vertical control of smoke and the largest thickness of smoke layer.Side wall smoke exhaust has poor longitudinal control of smoke,with the fastest smoke spread rate.The addition of a baffle can effectively alleviate the problem of inadequate longitudinal control of smoke exhaust from the side wall.(2)After the addition of longitudinal wind,the vertical distribution of the cross-sectional temperature,visibility,and CO concentration of the side wall smoke exhaust widens,the thickness of the smoke layer increases,and the longitudinal spread rate slows down.The effect of side wall + baffle smoke exhaust is not obvious.When the longitudinal wind speed is low,the addition of longitudinal wind can make the vertical distribution of the cross-sectional temperature,visibility,and CO concentration of top exhaust smoke exhaust smaller.The smoke returns to the top exhaust vent earliest.(3)In the construction of immersed tube tunnels,the smoke exhaust efficiency of top exhaust immersed tube tunnels is the highest,followed by side wall + baffle smoke exhaust immersed tube tunnels,and the smoke exhaust efficiency of side wall smoke exhaust immersed tube tunnels is the lowest.The addition of longitudinal wind can greatly improve the smoke exhaust efficiency of side wall smoke exhaust.However,it will cause a decrease in the smoke exhaust efficiency of the top exhaust and side wall +baffle smoke exhaust immersed tube tunnels,with the top exhaust efficiency decreasing significantly.(4)Owing to the incapability of software simulations to accurately reflect the psychological state of disaster victims and the actual evacuation status during a fire,the Pathfinder simulation yielded smaller evacuation times compared to the theoretical calculations of evacuation times obtained through mathematical models.(5)Free evacuation causes evacuating personnel to move towards the nearest evacuation door,and in smooth flow,crowds can be evacuated quickly.However,the free evacuation mode results in a large number of people gathering near the evacuation door close to the fire source,resulting in high danger.(6)The upstream evacuation mode can effectively solve the problem of personnel gathering near the fire source and reduce the evacuation pressure of nearby evacuation doors.However,due to the gathering of evacuees towards the upstream evacuation doors,the flow of people at the central part of the tunnel where the evacuation doors are located increased,resulting in an extended evacuation time.Therefore,changing the path did not result in a significant reduction in the overall evacuation time of the tunnel. |
