Settlement limit values for box subgrade of high-speed railway

To reduce the high cost of low-pier bridges, the huge demand for fillers, and the large occupancy area of traditional subgrade, a new type of concrete box subgrade structure has been developed in China. However, in high-speed railway operating conditions, the uneven settlement of the ground is inevitable, which affects the service performance of the concrete box subgrade and the running safety of the train. To obtain the settlement limits of the new type of concrete box subgrade structure, the influences of ground settlement on track deformation, force and vehicle dynamic responses were investigated in this paper. Taking both ballasted track and ballastless track into consideration, four types of settlement analysis were considered according to the structural characteristics, including box faulting, trapezoid settlement, V-shape settlement and box rolling. Based on the nonlinear finite element model of track-concrete box subgrade, the vertical fastener force and 10 m chord versine of vertical irregularity with different settlement types and values were investigated. Based on the train-track-concrete box subgrade dynamic model, the train dynamic responses with different settlement types, different settlement values and different running speeds were studied by adopting a real-time co-simulation method. On this basis, the settlement thresholds of concrete box subgrade were determined according to China’s codes. The results show that for the ballasted track-concrete box subgrade structure, except that the settlement threshold with box faulting at the speed of 350 km/h is determined by wheel unloading rate, the settlement thresholds of all the other settlement conditions are controlled by 10 m chord versine of vertical irregularity. For the ballastless track-concrete box subgrade structure, the settlement thresholds are not controlled by the dynamic indicators. The settlement thresholds with box faulting and box rolling are controlled by the vertical force of fasteners, and the settlement thresholds with trapezoid settlement and V-shape settlement are controlled by the 10 m chord versine of vertical irregularity. The settlement thresholds of ballasted track-concrete box subgrade with box faulting, trapezoid settlement, V-shape settlement and box rolling are suggested as 4.02 mm, 17.63 mm, 9.17 mm, and 5.53 mm, respectively. The settlement thresholds of ballastless track-concrete box subgrade are suggested as 2.48 mm, 17.43 mm, 8.79mm, and 2.55 mm, respectively. © 2023, Central South University Press. All rights reserved.