盾构隧道安全疏散通道加压送风计算分析

Calculation and analysis of the pressurized air supply for the evacuation passage of the shield-type tunnel

为防止盾构隧道行车道发生火灾时烟气侵入人员疏散通道,可通过在盾构隧道疏散通道内设置独立机械加压送风系统保证疏散通道内正压状态进行防烟,提高人员疏散安全性。分别利用风速法和压差法对某隧道工程疏散通道加压送风系统送风量进行试算,并采用FDS(Fire Dynamics Simulator)软件对疏散前室送风、疏散通道单侧送风及疏散通道双侧送风3种加压送风方式进行模拟分析,对比不同加压送风方式下各疏散口风速、温度、能见度的情况。结果表明,通过风速法计算得到的加压送风量要大于压差法。采用前室加压送风会造成较强的气流扰动,导致疏散口附近风速及温度剧烈波动,部分烟气进入前室,不利于人员疏散。采用疏散通道加压送风时,疏散口处风速稳定。但采用单侧加压送风时,火源下游疏散口处会有部分烟气积聚,影响人员疏散。采用双侧加压送风时烟气积聚少,疏散口附近温度、能见度等安全指标均在临界范围内,防烟效果良好,可以保证人员疏散安全。因此,建议采用纵向疏散通道加压送风,送风量建议采用风速法计算,当采用纵向疏散通道双侧加压送风时,建议在风速法得出的送风量基础上增加10%作为安全值。

This paper intends to provide its own approach to calculation and analysis of the pressurized air supply efficiency for the evacuation passage of the shield-type tunnel to prevent smoke invasion into the workmen evacuation from the passage. For the said purpose,we have calculated and worked out the air supply volume of the pressurized air supply system of the tunnel project through a fire dynamic simulation( short for FDS) in such a shield tunnel by using the wind velocity method and the differential pressure method. Specifically speaking,the simulation has been done in 3 different types of pressurized air supply mode,i. e. the antechamber’s air supply,the single side and both sides of the air supply of the evacuation passage. For example,to prevent the smoke and fire from invading into the personnel evacuation passage of the tunnel,we have managed to set up an independent mechanical pressurized air supply system in the evacuation passage of the shield tunnel to ensure the positive pressure of the passage to prevent from and improve the safety of the smoke evacuation. What is more,we have also made a careful comparison between the wind velocity of evacuation,the temperature and the visibility of the different air supply modes. As a result of the comparison,we have identified and determinated that the pressurized air supply volume by the wind velocity method proves to be greater than that given by the differential pressure method. This is because the antechamber air supply tends to cause strong airflow disturbance,and in turn result in the fluctuation of the wind velocity and temperature around the evacuation outlet. What is more,the smoke invasion into the antechambers tends to be harmful for the workmen evacuation. However,if the air supply system is installed in the evacuation passage,the wind velocity can be made stable for the evacuation spot. However,when the single side pressurized air supply is used,it would be possible to accumulate some smoke supply at the evacuation passage in the downstream direction of the fire source,which may influence the evacuation safety. But,in contrast,if the air supply can be done from both sides,there would be no smoke accumulation in the passage. Thus,the temperature and the visibility near the evacuation spot should be situated within the critical range in the regard of the smoke prevention. Therefore,it is recommended to use the pressurized air supply in the longitudinal evacuation passage,as well as the wind velocity method to calculate the air supply volume. And,in so doing,the wind speed method can help to increase the air supply volume and profitability by 10% of its original.