Long-term deformation mechanisms of double-track heavy-haul railway embankment under bidirectional shear loadings

During heavy-haul train crossings, embankments develop complex stress paths characterized by bidirectional principal stress rotation (PSR) spanning centerline, unloaded-track, and loaded-track zones. Assessing the long-term embankment deformation under cyclic traffic loading without considering the bidirection PSR effect may result in underestimation of the soil deformation. This study investigates the deformation mechanisms of double-track heavy-haul railway embankments subjected to cyclic traffic loading. Utilizing finite element simulated critical stress paths extracted from embankment cross sections, the uni- and bidirectional PSR scenarios are compared explicitly using variable-direction dynamic cyclic simple shear (VDDCSS) experiments. Results indicate that bidirectional PSR generate stress path across 3D space, contrasting with the single-plane confinement of unidirectional PSR. For equivalent depths underneath the tracks, vertical displacements under bidirectional PSR surpass unidirectional PSR values at both the embankment center and loaded line areas. Findings from this study demonstrate that bidirectional PSR modeling is crucial for accurately predicting the long-term settlement of heavy-haul railway embankments under cyclic traffic loads.