Comparative study on dynamic response of shield tunnel with crown and invert cracks under cyclic train loads

Cracks in shield tunnel linings have become a typical defect affecting structural safety. Existing research predominantly focuses on undamaged structures or single cracks, lacking a comparative analysis of the dynamic effects of crown versus invert cracks, and suffers from insufficient collaborative “experimental-numerical” validation, making it difficult to support precise crack management and control. This study employs numerical simulation to investigate the mechanism of crack influence, setting three working conditions: no crack, crown crack, and invert crack. The dynamic response is analyzed by combining time-domain analysis and one-third octave spectrum analysis. The results indicate that lining cracks significantly increase the structural dynamic response. Within the time domain, the acceleration amplitude at the crack location increases markedly, while in the frequency domain, vibration energy concentrates within the key frequency band of 0–50 Hz. The presence of lining cracks alters the local stiffness, mass, and damping characteristics of the tunnel structure, thereby affecting its dynamic properties. This leads to the concentration of vibration energy within specific frequency bands and the amplification of the dynamic response. This paper reveals the influence mechanism of lining crack location on the dynamic response of tunnels under cyclic train loads, providing a theoretical basis for risk assessment and repair of cracks in subway tunnels.