Experimental research on fire resistance of the reduced scale immersed tunnel with fire in both traffic tubes

摘要

? 2022 Elsevier LtdIn order to investigate the fire performance of concrete immersed tunnels, a large-scale model of an immersed tunnel was constructed, loading devices and two fire test furnaces were built at the same time. The fire test considered an extreme fire condition. Without fire protection, the fire test was carried out in both tubes of the tunnel at the same time. In the tunnel, the maximum temperature of fire exceeded 1300 °C. Under the service load, the tunnel was heated by fire for 245 min, and then the tunnel was cooled by ventilation for 360 min. During the fire test, the temperatures, deformations, cracking, spalling, and other behaviors of the tunnel were recorded. The test data provided the record of the structural damage and structural deformations of the tunnel under fire. The concrete spalling of the tunnel under fire was almost 100 %, and the maximum depth of the concrete spalling reached 142.2 mm. The inner rebars of the tunnel were exposed to fire, and some rebars melted. The mid wall suffered the severest damage, and it was the most dangerous of the tunnel under fire. However, the deformation of the tunnel was mainly caused by the axial deformation of each component, and it was very small. The test results showed that the bearing capacity of the tunnel under fire was sufficient, but the concrete cracking of the tunnel was very severe. During the fire test, affected by the thermal expansion and contraction of concrete, the unheated side and heated side of the tunnel alternately cracked, and the crack positions overlapped, which might cause through cracks inside the tunnel. In the case of sufficient bearing capacity of immersed tunnels under fire, concrete cracking can still cause disaster or reduce the durability of immersed tunnels. In the fire resistance design of immersed tunnels, measures should be taken to restrain the concrete cracking and improve the flexural bearing capacity of the mid wall under fire.