Study on the Stress Response and Deformation Mechanism of Pipe Jacking Segments Under the Coupling Effect of Defects and Deflection

Defects in pipes adversely affect both the jacking construction process and long-term operational safety, yet their specific impacts on mechanical properties remain unclear. This study investigates pipe jacking segments under deflection, using the Changsha Meixi Lake project as a case study. Similar model tests combined with digital image correlation were employed to examine the evolution of stress and deformation under various deflection angles and defect conditions. The reliability of the indoor test results is demonstrated using normalized parameters. The results indicate that stress distribution characteristics are jointly determined by the deflection mode and load. Co-directional deflection exhibits a more significant stress concentration effect; under identical load and angle conditions, it results in higher stress levels due to a superposi-tion effect, whereas diagonal deflection shows a weakening effect. Joint deformation progresses through three distinct stages: an initial linear strain-load relationship under stable deflection (load < 2 kN), followed by nonlinear strain growth with a slowing de-formation rate (2–4 kN), and finally a slow linear strain increment (load > 4 kN). In-creasing load and deflection angle significantly amplify axial deformation, particu-larly revealing a "thick-in-the-middle, thin-at-the-sides" compression characteristic in the 45° vault zones. Furthermore, segment defects markedly exacerbate stress non-uniformity. Defect angles ≥60° substantially increase the frequency and amplitude of compressive stress in the vault, accelerate the decay of tensile stress at the bottom, and critically reduce structural stability. These findings provide significant insights for deflection control and structural safety assessment in pipe jacking engineering.