A calculation method for vertical deformation of existing subway tunnels induced by short-distance dual-line rectangular pipe jacking over-crossing

Rectangular pipe jacking in utility tunnel construction inevitably intersects existing subway tunnels at close distances, inducing secondary disturbances that cause vertical deformation and operational risks. Therefore, this study establishes a deformation calculation model for dual-line rectangular pipe jacking, incorporating soil excavation unloading, pipe self-weight, drag-reducing slurry effects, and frictional resistance. At the same time, the equivalent friction coefficient and grouting rate were introduced, the additional stress coefficient of excavation unloading was defined, and the calculation formula of additional stress and vertical deformation of existing subway tunnels during the construction of dual-line rectangular pipe jacking was derived. A comparative analysis of engineering examples showed that the vertical deformation distribution characteristics of existing subway tunnels obtained by the calculation method proposed are similar to those by monitoring data. Comparative analysis revealed a 6% deviation between the calculated (5.3 mm) and monitored (4.9 mm) maximum vertical deformations, confirming the model’s reliability. Parametric analysis reveals that variations in twin pipe jacking spacing and average Poisson's ratio exert limited influence on deformation and additional stresses in existing metro tunnels. In contrast, pipe jacking excavation width and foundation elastic modulus trigger nonlinear responses in tunnel deformation and additional stresses. This confirms that excavation width and soil elastic modulus constitute the dominant governing factors for tunnel deformation. Disturbance magnitude decreases with larger dual-line spacing, while disturbance range expands. Increasing clearances, axis angles, and dual-line distances effectively mitigate vertical deformation. These findings provide actionable guidelines for minimizing risks in urban underground infrastructure projects.