Study Of Fire Characteristics And Smoke Control In Super Long Tunnels With Rescue Stations

With rapid development of tunnel construction in our country, there has being a large number of long and complicated road tunnels, and tunnel fire safety is becoming a focus nowadays. This thesis researches on the fire characteristics and smoke control in many scenarios in a super long tunnel including rescue stations, to provide theoretical evidence and references for determination of design of tunnel fire safety in a super long tunnel including rescue stations.Based on the analyses of interaction of ventilated flow with plume flow, this thesis analyzes the fire characteristics in a tunnel fire, including maximum excess gas temperature beneath the tunnel ceiling, the deflection angle, the flame length, ceiling temperature distribution, vertical temperature distribution in different cross-sections, heat release rate and fire growth rate. The results show that the maximum excess gas temperature can be divided into two zones, and the most important parameters involved are the maximum heat release rate, the longitudinal ventilation velocity, the modified tunnel height and the geometry of the fire source. The deflection of the flame in a ventilated flow is directly related to a dimensionless ventilation velocity, which takes the heat release rate, the ventilation velocity and the geometry of the fire source into account. The flame length in a large tunnel fire is proportional to the heat release rate and almost independent of the ventilation velocity. The ceiling temperature distribution can be correlated well using two natural exponential functions with a dimensionless distance away from the fire site. The maximum heat release rate and the fire growth rate are intimately related to the longitudinal ventilation velocity. Normally a tunnel fire is well ventilated and fuel-controlled, and the maximum heat release rate is independent of the ventilation velocity and the fire growth rate is proportional to the ventilation velocity. In other words, the longitudinal ventilation has influence on the fire growth rate rather than the peak heat release rate under the condition. It is also shown that the peak heat release rate in a tunnel fire may be lower than in an open fire, and so is the fire growth rate.Smoke control in a longitudinally ventilated tunnel fire is a focus in the fire safety design of a given tunnel. The critical velocity and the back-layering length are analyzed based on dimensional analysis and tests data, and specific formulae that correlate well with tests results are proposed. The results show that there is a tight relationship between them. When a tunnel fire is small, both of them are related to the heat release rate, however, independent of the heat release rate when the fire gets very large. The effect of obstruction of a vehicle on the smoke control is also analyzed. The results show that the decrease rate of critical velocity due to obstruction is slightly greater than the ratio of cross-section area of the model vehicle to tunnel cross-section area, and the back-layering length with an accident vehicle set inside the tunnel gets smaller.The cross-passages between two tunnels are designed for evacuation during a tunnel fire. Based on the assumption of a constant critical Froude number, a theoretical model called Froude model is proposed. Although the tests data show the critical Froude number is not a constant, the influencing parameters involved in are known and then used for dimensional analysis. The effect of geometry of a fireproof door in a cross-passage, the tunnel ventilation velocity, and the heat release rate is analyzed. The results show that the critical velocity in a tunnel cross-passage varies approximately as 1/3 power of the heat release rate, as the exponential law of the ventilation velocity, as 3/2 power of the fireproof door height, and almost independent of the fireproof door width. A correlation for predicting the critical velocity in a tunnel cross-passage was proposed. The theoretical results fit the tests data well.The types of structure of a rescue station in a super long tunnel and its emergency ventilation systems are analyzed. Two types of rescue stations are classified. The influence of the effective length of a rescue station and effective height of the blocks are analyzed and simplified method of carrying out model-scale rescue station fire tests is obtained. A series of rescue station fire tests was conducted based on the simplified method. The smoke control in a rescue station with and without a train placed inside the model tunnel is analyzed. The basic rule of distribution of the critical velocities in different cross-passages is obtained. According to theoretical analysis, the critical velocity in a tunnel cross-passage is directly related to the gas temperature beside the fire-proof door at the door height. In other words, the gas temperature beside the door can be predicted if the critical velocity is determined. A specific requirement for fireproof door height is also proposed based on these analyses. The temperature distribution in the rescue station and the cross-passages is also analyzed, and the basic rule of gas temperature distribution along the ceiling of the cross-passage is obtained.A method combing one-dimensional method and three-dimensional method was used to analyze the emergency ventilation systems used in two rescue stations of Taihangshan super long tunnel. The ventilation scheme C and E is better than others for Rescue stationâ… and scheme B for Rescue stationâ…¡. The distribution of the velocities in tunnel cross-passages gets much more uniform if the shaft turns its direction to make the air flow in the shaft inject into the rescue station with a right angle. The minimum velocity in the cross-passage is about 0.7 m/s if the length of the section is 1D (one time its hydraulic diameter), and 1.4 m/s 2D (two times its hydraulic diameter). The measure widening the connector based on 1D long section has nearly no effect on the distribution of velocities in the cross-passages.A series of model scale tunnel fire tests with automatic water spray system was carried out. The actuation time, actuation condition of the bulbs and collapse of an automatic water spray system were analyzed. The results show that the actuation heat release rate of the first bulb is proportional to the longitudinal ventilation velocity, and all the actuated nozzles are activated in a range of about 1 min to 2 min (full-scale 4 min to 8 min), and normally the actuated temperature is little higher than the link temperature. The high longitudinal ventilation velocity and the low water flow rate result in collapse of an automatic water spray system. An appropriate zone avoiding the collapse of a system is proposed.