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The fire risks in the tunnel mainly include passengers' luggage, risky goods, and vehicles and tunnels themselves.
The purpose of the fire safety control of the tunnel is mainly to provide possible decentralized equipment, to reduce the number of casualties, to facilitate rescue and fire extinguishing operations, to prevent the explosion of the concrete liner in the tunnel and to protect the tunnel structure and equipment, and to reduce the tunnel repair and tunneling. The loss formed by the patch. In the design of fire protection for highway tunnels, it is necessary to think about structural fire resistance and collapse prevention, reduce the extinguishing performance of data in tunnels, set fire detection and alarm, and monitor signal systems, plan and set up separation, rescue, decentralization and refuge emergency systems, and smoke control. System and so on.
Construction of the tunnel maintenance within <br> <br> tunnel fires often longer duration, such as MontBlanc tunnel fire continued 55h, 36 vehicles were involved in the fire. The study indicated that after the concrete structure is exposed to heat, it will burst, and after the concrete base is cooled, deep cracks will appear. The higher the constructed load pressure and concrete moisture content (including physical water content and molecularly separated water), the greater the likelihood of cracking and even the participation of polypropylene fibers in the concrete mix will not significantly improve. Unmaintained concrete, if its mass moisture content exceeds 3%, will burst within 5-30 minutes after encountering high temperature or flame effects, and can reach depths of up to 40-50mm. This is the main reason for tunnel collapse. Normally at 150-200°C, the concrete begins to burst at the beginning.
The tunnel structure is round, rectangular or arched. The failure of the rectangular structure is usually caused by the rise of the temperature of the concrete or its reinforcing steel leading to the premature emergence of plastic bending moments. The rectangular tunnel has a smaller pressure load than the circular tunnel, resulting in a lighter burst condition. Reinforced steel bars in circular tunnels do not receive tension under sagging bending moments and only accept pressure loads. Shield-type circular tunnels usually use high-grade concrete with a grade of C50, and are highly likely to burst in fire.
After the concrete bursts, it not only directly requires rescue and escape, but also makes the reinforcing steel directly exposed to the fire and reduces the cross-sectional area of ​​the bearing structure. Therefore, the fire resistance design of a tunnel structure should consider the maximum temperature, temperature rise characteristics, and fire behavior of the structure that can be reached within the tunnel structure. The fire range and time-temperature curve must be set accordingly to ensure that the tunnel structure is under the fire conditions of the regular type. The integrity and stability.
Refractory maintenance of tunnel structures can be done by adding polypropylene fibres to the concrete or by means of a fireproof thermal insulation maintenance layer under the concrete lining, or by installing an automatic sprinkler system in the tunnel.
A tunnel is a relatively locked space that is directly connected to the outside world. The limited escape conditions in tunnels and the removal of hot smoke from the exits have caused tunnel fires to extinguish, with faster temperature rise in the surrounding area after four weeks of extinguishing, long duration, large fire range, and difficulties in fire fighting and entry, which has increased the lives of scattered and rescue workers. Risks, tunnel linings and structures are also destroyed, and their direct and indirect losses are huge. Therefore, it is necessary to consider the fire protection measures in the tunnel design.