To investigate the differences in the deterioration behaviors of subway shield tunnels under various loading conditions,the full-scale test was conducted to comparatively analyze the evolution patterns of segment deteriora-tion under different load scenarios,summarizing the characteristics of shield tunnel structural deterioration.The re-sults indicate that the primary impact of loading and unloading states on shield tunnel segments is the disruption of force equilibrium and alteration of constraint conditions,thereby changing the evolution process of deterioration.The convergence deformation and stress variations of segments exhibit entirely opposite trends under symmetric loading and unloading.In the final stage of asymmetric unloading,the maximum positive and negative convergences of segments occur at 90°and 180°,respectively,with bolt stress undergoing multiple polarizations.Concrete cracks concentrate near the bottom of the arch crown,distributed at a 45°angle.In the final stage of asymmetric surcharge loading,the maximum positive and negative convergences are located at 90°and 30°,respectively.Bolt stress follows a linear pattern,and concrete cracks first appear at the arch haunch corners and are distributed at a 180°angle.
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