Study On Mechanical Properties Of Submerged Tunnel In Water Mist Fire Extinguishing

Fire is a catastrophic burning phenomenon,and tunnel,as the main traffic mode of underground space,plays an extremely important role in the solution of urban traffic pressure.At the same time,due to the closure of the tunnel environment and the difficulty of personnel evacuation,once a fire occurs in the tunnel,it often causes great casualties and economic losses.Water mist fire extinguishing technology has the advantages of high efficiency,environmental protection,water saving,smoke washing and so on.It is of great significance for the development of tunnel fire safety technology and the popularization and application of water mist fire extinguishing technology to study the mechanical properties of immersed pipe tunnel under the action of water mist in fire.This paper takes the immersed tube tunnel of yuanhe tangxi tunnel project in suzhou city,zhejiang province as the prototype,builds an experimental model of immersed tube tunnel according to the scale of 1:10,and measures the fire field temperature with thermocouples in natural ventilation conditions to obtain the fire heating curve.By using the measured fire heating curve and using the finite element analysis software ABAQUS to simulate and analyze the temperature field changes of the immersed tube tunnel under natural ventilation conditions,the temperature time curves of 18 different measuring points of the section top of the immersed tube tunnel,the outer wall and the inner wall were obtained.The displacement cloud diagram of the tunnel,the time displacement curve of each measuring point and the time stress curve are obtained.Results show that the natural ventilation condition of sinking pipe tunnel has the highest surface temperature of 572.5℃,respectively,and the protective layer of reinforced concrete surface temperature is 167.5℃,GINA water-stop at the highest temperature of 26.62℃.The maximum stress on the top of the tunnel is 48.07MPa,and the maximum displacement in the vertical direction is 7.95mm downward at normal temperature.With the rapid rise of the fire temperature,the displacement decreases to 4.09mm downward.Thermal expansion causes the overall displacement of the tunnel to be 3.86mm upward,reaching 48.49%.The horizontal displacement of outer wall and inner wall at room temperature is 0.63mm and 0.55mm respectively.With the rapid rise of fire temperature,the maximum horizontal displacement of outer wall and inner wall reaches 6.81 mm and 1.61 mm,increasing by 980.95%and 191.09%respectively.Furthermore,the same model was used to carry out the fire extinguishing experiment of water mist,adjust the pressure of water mist,test and compare the evolution process of fire field temperature under the action of water mist.ABAQUS was used to compare and analyze the influence of fine water mist on tunnel temperature field,and then thermodynamic coupling simulation was carried out.Compared with no fire extinguishing measures,the influence of fine water mist with different pressures on immersed pipe tunnel was obtained.Results show that under the water mist fire extinguishing of steel surface temperature less than 100℃,without reinforcement of water mist fire extinguishing temperature as high as 167.5℃,2MPa water mist can decrease the thermal expansion deformation of 11.25%,and 6MPa water mist can reduce 30.50%,2MPa and 6MPa water mist GINA water-stop at the highest temperature of 24.87℃ and 24.66℃ respectively.It can be seen that fire extinguishing with fine water mist can greatly reduce the temperature of steel bars and the damage of high temperature to the mechanical properties of steel bars.