Experimental investigation on fire damage to staggered segmental lining of shield tunnel

Fire is a significant hazard to the safe operation of tunnels, causing extensive damage and deterioration to the lining. This research proposed a prototype test of a shield tunnel staggered segmental lining under stratum loads subjected to fire. The fire followed the ISO834 standard curve; the maximum temperature reached 1144.9 degrees C and lasted 195 min. The temperature evolution law of the lining is positively correlated with the distance from the fire source and negatively correlated with the depth of the lining. The fire surface of the lining undergoes severe cracking and peeling, accompanied by water seepage and water vapour escaping during the fire. The concrete spalled severely on the fire surface of the lining, the maximum depth and area reached 65 mm and 3.05 m2, respectively, and the reinforcement near the fire source was exposed after the fire. The mechanical behaviour of the entire lining was damaged by fire, and that in the fire area was more significant than that in the non-fire area, and the damage degree of the joint was more significant than the segment. Every mechanical parameter of the lining changes significantly during the firing process and only partially recovers during the cooling, with significant residual values. The ultimate bearing capacity of the lining after being damaged by fire was about two times the preset stratum load. And the failure characteristic of the lining damaged by fire was the plastic failure of the joints in the fire area. Specifically, in the fire area, there were numerous wide cracks, some joints were crushed, and some inner reinforcement yielded, while in the non-fire area, there were only a few micro-cracks on the segment and a few cracks on the joints. The research conclusions can also provide a reference for the post disaster assessment of tunnel fire.