Investigation of loading intensity effect (LIE) on the failure mechanism of shield tunnel subjected to fire

The overload damage seriously threatens the service life of the tunnel structure, and the elevated temperatures under the extreme load of fire pose a more serious threat to the structure. In this study, a thermal-mechanical methodology is proposed to analyze the combined effects of loading intensity and fire on tunnel structures. The methodology is also validated by experimental studies. Impacts of loading intensity effect (LIE) on temperature distribution, deformation development and inner force distribution are discussed respectively. Results indicate that LIE aggravates heat flow invasion, making uneven temperature distribution of the segmental ring. On the other hand, LIE has a direct influence on the development of mid-span deformation of lining segments, and induces the failure of lining segments due to excessive deformation at the initial stage of heating. higher loading intensity induces a higher initial axial stress level of the tunnel structure. It is also found that the failure of the segmental ring can be attributed to the development of plastic hinges originated from the coupled thermo-mechanical effect. The findings not only reveal the combined effects of overload damage and fire on tunnel structures, but also provide valuable insights on fire prevention in case of tunnel fire.