Research on zoning of soft rock large deformation considering state of ballastless track and train comprehensively based on FEM-MBD

Severe foundation heave arises during tunnel excavation and operation, especially in the soft rock sections, detrimentally impacting track service performance and train operational safety. To elucidate the mechanisms by which foundation heave affects track structures and vehicle dynamics, and enable refined management of ballastless tracks in heave-affected sections, this study proposes a foundation deformation zoning method based on FEM-MBD (Finite Element Method-Multi-Body Dynamics). A refined failure analysis model for ballastless tracks and a rigid-flexible coupled dynamic model of the vehicle-track-foundation heave system are constructed to investigate "foundation deformation – ballastless track state – train operational performance" chain transmission law including deformation transfer mechanisms, structural damage evolution, interlayer contact damage progression, and vehicle dynamic responses under foundation heave conditions. Foundation heave zoning is further implemented by synthesising multiple control indicators, informed by the established static-dynamic mapping relationship. Results demonstrate that foundation heave propagates to all track structural layers, with structural damage, interlayer contact damage, and vehicle dynamic response indicators deteriorating under "short-wavelength + large-amplitude" foundation heave. Four distinct foundation heave zones are defined, and targeted management recommendations are proposed for each zone. This research provides scientific support for safe of ballastless track under foundation heave.