Methods for determining multiple hazards and response analysis of metro shield tunnels considering existing structural damage

The article proposes a method for determining multiple hazards during the operational period of metro shield tunnels and preliminarily investigates the multiple hazards response of tunnel structures considering existing structural damage. Specifically, the study first identifies the components of multiple hazards for metro shield tunnels based on historical disaster data. Then, Bayesian theory is used to develop a method for determining the types of multiple hazards relevant to a specific tunnel, considering hazard impact factors and propagation mechanisms. Furthermore, the load probability distribution function for each hazard and hazard chain is given based on a large amount of disaster data. Finally, numerical calculations are used to examine the structural response and damage characteristics under different existing damage conditions (including cracks, material deterioration, segment dislocation, and varying degrees of convergence) and multiple hazards (including train impact, fire, and continuous action of both). The main conclusions are as follows: The proposed method addresses the inadequacy in existing codes that consider fire and earthquake by incorporating various other hazards other than as outlined. The degree of convergence significantly influences the subsequent structural hazard response. Both the percentage of concrete damage and the maximum damage factor for the chain hazard were significantly greater than for the single hazard. The findings enhance the understanding of structural response and damage characterization of shield tunnels in multiple hazards, with consideration of existing structural damage.