Fuzzy decision-driven multi-dimensional seismic fragility analysis of shield tunnels in liquefiable strata

Accurate seismic fragility analysis is essential for ensuring the post-earthquake safety of shield tunnels in liquefiable strata. Current fragility methodologies predominantly adopt empirically selected ground motion intensity measures (IMs) and single damage measures (DMs), while overlooking uncertainties stemming from sampling insufficiency and inhomogeneity. This study presents an advanced fragility analysis framework to systematically address these limitations. Initially, a computational model of a shield tunnel in liquefiable strata is developed and validated through experimental and theoretical simulations. Subsequently, fuzzy probabilistic seismic demand models are established considering uncertainties in model parameters based on nonlinear dynamic analysis results. Progressing to the fuzzy decision-making phase, an approach integrating fuzzy analytic hierarchy process and fuzzy technique for order preference by similarity to ideal solution is implemented to quantitatively determine the optimal IM. Finally, multi-dimensional fragility analysis is conducted, using the DMs reflecting tunnel deformation and uplift. The results reveal that sustained maximum velocity, as the optimal IM, produces more conservative estimates of tunnel damage probability than the conventional IM, peak ground acceleration. Moreover, the implementation of multi-dimensional fragility analysis incorporating dual DMs yields significantly improved reliability in seismic risk assessment.