Development Analysis of I-Longitudinal Crack in the Vault of Underwater Tunnel Secondary Lining

Abstract

In this paper secondary lining of an underwater tunnel which had appeared I-longitudinal crack was taken as study object according to theory of fracture mechanics. Finite Element analysis was carried out to calculate the stress intensity factor at the tip of I-longitudinal crack which located in vault, then to analyze the extended state of crack based on double-K fracture criteria. The computation results indicate that the stress intensity factor at the tip of I-longitudinal cracks which appear within 20 degrees of the vault do not exceed unstable fracture toughness, lining is in stable growth stage and do not occur instable failure. The stress intensity factor at the tip of I-longitudinal cracks appeared in vault is maximum and appeared in both side of vault is minor, the further away from vault the less of stress intensity factor. When water level below the top of tunnel, with the rise of water level the stress intensity factor at the tip of I-longitudinal decrease and the external water pressure has restrain effect to the crack extension. When water level exceed the top of tunnel, with the rise of water level the stress intensity factor at the tip of large depth of crack decrease rapidly until arrive negative value, then increase backward until greater than unstable fracture toughness and cause lining structural local instable failure.