Study On The Large Fire Simulation And Safety Evacuation Of People In Mountain Road Tunnel

With the rapid growth of traffic,the tunnel plays an important role in the road,especially in mountainous area.However,due to the narrow and long,semi-closed and other characteristics in tunnel structure,when the tunnel fire,often because of unreasonable ventilation smoke,the tunnel structure will be damaged by high temperature,and the trapped personnel in the tunnel will also be affected by high temperature smoke,such as high temperature damage to human function,CO excessive poisoning and reduced visibility range,seriously hinder the safety of the trapped personnel evacuation,it may even lead to casualties among those who escape.Therefore,according to the large fire caused by heavy trucks,this thesis studies the fire smoke development law of mountain road tunnel with horseshoe section mainly under different longitudinal ventilation conditions and the evacuation situation of trapped personnel.It not only supplements and improves the fire theory of highway tunnel,but also provides theoretical basis for fire prevention,personnel evacuation and safe operation of highway tunnel in mountainous areas,which has important scientific value and engineering significance.In this thesis,the Pyrosim simulation software is used to establish a large fire burning model of mountain road tunnel.By changing the longitudinal ventilation speed,the development law of fire smoke,temperature,CO concentration and visibility in the tunnel is studied.The damage range of high temperature smoke in different longitudinal ventilation to the tunnel structure is analyzed.The available time for safe evacuation of trapped persons upstream of the fire source was determined.The results show that without longitudinal ventilation,the smoke spread,temperature distribution,CO distribution and visibility distribution in the tunnel show symmetry,and the high temperature smoke mainly gathered at the top of the tunnel.Under the action of longitudinal ventilation,the smoke spread,temperature distribution,CO distribution and visibility distribution in the tunnel are not uniform.And with the increase of longitudinal ventilation speed,the high temperature smoke upstream of the fire source can be effectively controlled.Longitudinal ventilation can reduce the temperature in the tunnel and reduce the damage range of high temperature to the tunnel lining structure.The speed of longitudinal ventilation is controlled at 4.5 m/s < v ≤ 6 m/s,it can ensure the safety of tunnel lining structure in the case of large fire and the high efficiency and low cost of ventilation in the process of tunnel operation.In the case of low longitudinal ventilation speed(such as v=1.5 m/s),the visibility index upstream of the fire source is lower than 10 m,which cannot meet the requirements for safe evacuation of personnel,making trapped personnel in a dangerous state during evacuation.According to the criterion of the available time of evacuation,the available time of evacuation of trapped personnel under the action of small longitudinal ventilation speed(such as v=1.5 m/s)is determined to be 730 s in large fire of mountain road tunnel.In this thesis,the Pathfinder simulation software is used to establish the personnel evacuation model of mountain road tunnel.According to the layout of pedestrian transverse passage in the Tuzhu tunnel,the fire source is located at different pedestrian transverse crossings,the evacuation process of trapped personnel in the tunnel is analyzed,the required time of personnel safe evacuation is determined.And combined with the available time of personnel safe evacuation,the evacuation safety of trapped personnel under large fire and small longitudinal ventilation(such as v=1.5 m/s)is analyzed.The results show that when the location of the fire source is changed,the number of trapped people passing through a pedestrian cross passage near the fire source in the free evacuation process is the largest and the evacuation movement time is the longest.With the increase of the distance from the fire source to the tunnel entrance,the number of trapped people in the tunnel presents a linear increase,and the evacuation movement time presents a trend of increasing,decreasing and increasing.When the fire source is at No.1 pedestrian crossing,the trapped personnel are in a safe state during evacuation,while when the fire source is at other pedestrian crossing,the trapped personnel are always in a dangerous state during evacuation.In order to ensure the safe evacuation of trapped personnel,when a large fire occurs in mountain road tunnel and a small longitudinal ventilation(such as v=1.5 m/s)is applied,it is recommended to open the pedestrian and vehicle transverse passages at the same time or optimize the design of the pedestrian transverse passages.While keeping the total width of the transverse passage unchanged at 44 m,the width of a single transverse passage is changed and evenly distributed in the tunnel,so as to achieve the purpose of the optimal design of the transverse passage.When the fire source is 2000 m away from the tunnel entrance,the evacuation process of trapped people is simulated.The evacuation movement time of trapped people under different transverse passage widths is analyzed.The required time of safe evacuation is determined,and combined with the available time of safe evacuation,the evacuation safety of trapped people is analyzed.The results show that when the width of a single transverse passage is changed,the evacuation movement time and the average flow rate of the transverse passage increase with the increase of the transverse passage width.After the optimization of the transverse passage,the trapped personnel in the tunnel can meet the safety escape under the combined action of large fire and small longitudinal ventilation(such as v=1.5m/s).With the decrease of the transverse passage width,the safe evacuation time increases,and the trapped personnel will be safer in the evacuation process.However,considering the design specification,construction cost and evacuation safety,when a large fire occurs in mountain road tunnel and a small longitudinal ventilation(such as v=1.5 m/s)is applied,the width of the transverse passage should be designed as 2.93 m and the spacing between adjacent transverse passages as 260 m.