Performance-based seismic assessment of shield tunnels by incorporating a nonlinear pseudostatic analysis approach for the soil-tunnel interaction

The purpose of this study is to present an efficient and reasonable methodology to evaluate the seismic fragility of shield tunnels based on investigating the seismic performance of segments and joints in detail. The finite element model of segments and joints is established using appropriate constitutive models and elements. A pseudostatic soil-tunnel interaction analysis approach based on the multimodal adaptive pushover of the 1D freefield model is introduced to improve the computational efficiency. The seismic performances of a shield tunnel, including the plastic strain of the segments, joint deformation and bolt yielding, are investigated by pseudostatic analysis, and the entire failure process is summarized. Therefore, a framework for seismic fragility assessment of shield tunnels is proposed. The scaling approach substituting the pseudostatic soil-tunnel analysis for traditional incremental dynamic analysis is adopted to consider the uncertainty of input motion. A Monte Carlo simulation is carried out to consider the uncertainties of soil and tunnel properties. The damage state levels are divided based on the crucial events during the failure process. Finally, the seismic fragility curves are fitted with normal and log-normal cumulative distribution functions. And the effect of the sampling size is discussed. Moreover, the seismic fragility curves taking PGA as IM are also obtained and compared with the existing seismic fragility curves in previous studies.