Failure process and damage assessment of prefabricated frame tunnel joints under internal explosion load

The vulnerability of tunnel structures to terrorist attacks and accidental explosions is obvious, but the failure process of explosions is complex and unknown. This study takes a practical prefabricated frame tunnel as an example and establishes a numerical model of the dynamic response of prefabricated frame tunnels based on the Conwep explosion load algorithm. Three different joint forms are considered to analyze the dynamic response law of the whole process of prefabricated frame tunnels under different explosive charges and different explosive distances. The results show that, owing to their insufficient stiffness, the central displacement values of the mortise–tenon and sleeve joints increased approximately linearly with time at a stand-off distance of 1 m and a TNT equivalent of 227 kg. The steel box joint exhibits better resistance to explosions. The damage to tunnel structures mainly concentrates on the roof, floor, and middle partition wall, which are easily affected by explosive loads and are prone to forming strong damage areas. Taking the weak part of the tunnel, the middle partition wall, as the research object, the damage level of the middle partition wall structure is accurately predicted based on a machine learning model.