Modal energy-based nondestructive identification of longitudinal cracks in circular tunnel linings through experimental and numerical analysis

This study presents a modal energy-based method for identifying longitudinal cracks in circular tunnel linings. The framework addresses limitations in physical interpretability and regional damage localisation under sparse sensor conditions found in existing vibration-based techniques. It integrates operational modal analysis with bandwidth-aware decomposition to extract mode-specific responses under train-induced excitation. A set of physically grounded indicators is defined to quantify intra-modal disturbance and cross-modal energy redistribution. A two-stage strategy is proposed, comprising a disturbance screening phase for anomaly detection and a template-matching scheme for region-level crack localisation. The method is validated through scaled physical experiments and finite element simulations. Blind tests across various crack scenarios confirm its reliability. The proposed approach contributes by introducing an interpretable energy-based indicator system, establishing a structured identification framework suited to sparse layouts, and validating spatial energy disturbance mechanisms through combined simulation and physical testing. The method emphasises robustness, physical clarity, and applicability to practical tunnel monitoring environments.