Response and seismic resilience of metro tunnels under normal fault dislocation evaluated based on the quantitative method of concrete damage state

The damage to tunnels crossing active fault zones caused by earthquakes can be of a severe and irreversible nature. The paper defines the quantification of the concrete damage state based on the uniaxial compression equation and the tensile-compression curve equation. Furthermore, the paper refines the concrete damage level in conjunction with the damage factor and crack width formulas, which is one of the most significant factors affecting the durability of concrete. A three-dimensional refinement model, constructed using ABAQUS software, was employed to analyse the mechanical response and seismic resilience of the tunnel structure under normal fault displacement with variable section mitigation measures. The model incorporated a number of key parameters, including fortification length, joint location and thickness. The following conclusions were obtained: the tunnel structure is susceptible to tensile damage and the damage is widely distributed under normal fault d; the use of variable section measures can help improve and reduce the overall damage of the cross-fault metro tunnel structure; the use of tensile damage state classification to assess the damage of the tunnel structure can determine the location and extent of the damage; an appropriate protection length is required, too long/short does not maximise the mitigation effect of setting variable section measures; an appropriate lining length is required; and the lining structure is not suitable for the tunnel structure. An appropriate location and thickness of the lining structure will help to reduce the overall damage to the structure. The application of localised reinforcement to the structure, in conjunction with variable section, serves to minimise the probability of collapse of the tunnel as a whole and to enhance the seismic resilience of the underground structure across the active fault zone.