Study On Fire Smoke Spread And Control In Double-deck Shield Road Tunnels

As an important part of the traffic network system,tunnel plays an important role in alleviating urban traffic pressure,improving travel efficiency and improving traffic environment.In view of the importance of tunnel in the modern transportation system and the particularity of its spatial structure,the tunnel operation safety,especially the fire safety,has become the focus of the society.The continuous innovation of smoke exhaust arrangement in double-deck shield road tunnel brings challenges to the design of tunnel smoke exhaust system.Aiming at the double-deck shield tunnel with smoke exhaust from the lower branch pipe and smoke exhaust from the top of the upper layer,a reduced size model experiment and full-size numerical simulation are carried out to systematically study the fire smoke spread characteristics and control strategies of this type of tunnel.The smoke temperature characteristics and spread control law of doubledeck tunnel under different smoke exhaust modes and modes are revealed.The main research work completed is as follows:(1)Based on the Froude similarity principle and taking a typical underwater double-deck tunnel as the research object,the 1:8 reduced size double-deck shield road tunnel fire model test platform was built,which was equipped with the smoke exhaust function of the lower branch pipe and the top of the upper layer,and the multi-parameter fire model test data acquisition system was configured.(2)Based on the built tunnel fire model experiment platform,57 fire experiments were carried out aiming at the two smoke exhaust modes of the tunnel roof and the branch pipe.In the experiments,the influence of key factors such as fire source power,smoke exhaust volume,length to width ratio of smoke exhaust outlet,opening scheme of smoke exhaust outlet(number and distance of smoke exhaust outlet)on the temperature characteristics of fire smoke and the spread range of smoke were considered.Based on the control of fire smoke spread range,combined with the results of reduced size experiment and full-size simulation,it is proposed that for the tunnel with fire size less than 15 MW,opening two smoke vents near the fire source can control the smoke spread in the minimum range,which has a better smoke exhaust effect.(3)Through dimensionless analysis of the experimental data,the prediction model of ceiling maximum temperature rise under the branch pipe smoke exhaust mode was established.According to the exponential attenuation trend of the temperature under the upper and lower ceiling of the fire source along the tunnel,the prediction model of the longitudinal attenuation of flue gas temperature in the upper and lower ceiling of the fire source was established.Based on the influence law of fire scale and exhaust volume on smoke spread distance,a prediction model of smoke spread distance under top exhaust mode was established.(4)The CFD simulation model of full-size tunnel fire was constructed.Based on the comparison and verification with the experimental data of the reduced size model,the fire scale was extended to 15 MW design fire condition.The simulation results were used to supplement and verify the experimental data and rules of the model.Compared with the branch pipe exhaust,the smoke spreading distance of the upper and lower fire source is shortened.Under the condition of opening unilateral exhaust fan,the top exhaust shortens the spread distance of the smoke near the exhaust fan,but increases the spread distance of the smoke away from the exhaust fan.Under the same exhaust opening scheme,the top exhaust efficiency is significantly higher than that of the branch pipe exhaust.(5)Considering the fire location and the opening mode of the smoke exhaust fan(opening single-sided or symmetrically on both sides of the smoke exhaust fan),the study on the smoke exhaust control strategy under the design fire condition of the tunnel was carried out,and the influence of the opening mode of the smoke exhaust fan under the same smoke exhaust opening scheme on the smoke control effect was analyzed when fire broke out in the middle of the tunnel and at the exit.The results showed that the opening mode of the exhaust fan has little influence on the smoke spread,and the symmetrical opening of the exhaust fan on both sides has better smoke exhaust effect.