Analysis of settlement thresholds for a new ballastless track-concrete box subgrade structure

In this paper, the effects of settlement on force, track deformation, and train dynamics to determine the settlement thresholds of ballastless track-concrete box subgrade (BTCBS) are studied. Firstly, this study introduces four settlement types, namely V-shape, box rolling, box faulting, and trapezoid settlement. The nonlinear finite element model (FEM) of BTCBS and the train-ballastless track-concrete box subgrade (TBTCBS) model considering nonlinear contact between track slabs and base slabs are established. Then, the effects of settlement on fastener force, track deformation, and vehicle dynamics are studied. According to the calculated results and China's codes, the settlement limit values of BTCBS can be obtained. The results indicate that the settlement thresholds with box rolling and faulting are controlled by vertical force of fasteners, and the settlement limit values with V-shape and trapezoid settlement are controlled by 10 m chord versine of vertical irregularity (CVVI). The suggested settlement limit values of BTCBS for box faulting, box rolling, trapezoid, and V-shape settlement are respectively 2.48 mm, 2.55 mm, 17.43 mm, and 8.79 mm.