Effects of settlement in the subgrade-bridge transition section on slab track deformation and damage

Slab track is highly sensitive to subgrade deformation, particularly at subgrade-bridge transition section, where abrupt stiffness changes govern structural response and durability. In this study, a three-dimensional slab track model on the subgrade-bridge transition (ST-SBT model) is developed to simulate the coupled response of a slab track, subgrade and bridge. The plastic damage of the track concrete is represented by a concrete damaged plasticity model. This model is used to study the vertical deformation, interlayer separation, and damage evolution under the combined effects of semi-cosine and folded-angle non-uniform settlement, overall abutment settlement, and the combined action of abutment settlement and train loads. The results indicate that a short transition section significantly amplifies structural responses. For a transition length of 5 m and a folded-angle settlement of 20 mm, the track slabs and base slabs will suffer severe tensile damage. However, when the transition length exceeds approximately 10-15 m, both deformation and damage will significantly decrease. Overall abutment settlement leads to a high concentration of deformation and damage at the beam ends and the abutment-subgrade joints. As the settlement continues to increase, strip-like cracks will appear in this section of slab track. Coupled train loads will further increase vertical displacement, uplift force, and interlayer separation, and may even induce tensile damage at relatively small levels of settlement. These findings from the ST-SBT model provide a quantitative basis for the rational design of transition section lengths, control of abutment settlement limits, and monitoring and maintenance of slab track in subgrade-bridge transitions. • 5 m transition length with 20 mm folded settlement causes severe tensile damage to track slab and base slab. • Transition length over 15 m significantly reduces deformation and damage of the slab track structure. • Abutment settlement leads to deformation concentration and strip cracks at beam ends and joints. • After coupling the train load, both displacement and interlayer separation are increased to varying degrees, and when the settlement is small, it can cause tensile damage. • ST-SBT model provides quantitative basis for transition section design, settlement control and maintenance.