Experimental Investigation of Cracking Behavior in Reinforced Concrete Immersed Tunnels Under Fire

To investigate the cracking behavior of reinforced concrete immersed tunnels under fire, a 1:5 scale model was constructed, and a fire test was conducted using the HCinc curve in the traffic tubes on both sides of the tunnel. The temperature field changes of the immersed tunnel were measured using thermocouples and infrared thermography. Infrared thermography was used to monitor the continuous temperature field on the ceiling outer surface and the temperature changes of concrete cracks. Based on the principle of water migration in concrete, the temperature of water and vapor in concrete cracks, and the temperature field in concrete, it was inferred that the depth of concrete cracks exceeded 150mm at 95 minutes of the fire test. In the event of a fire inside the immersed tunnel, the thermal expansion of the inner concrete exposed to fire can easily lead to the tensile cracking of the outer concrete. Therefore, in the fire resistance design of immersed tunnels, consideration should be given to concrete cracking caused by thermal strain.