Xin Li

Bio: Xin Li is an academic researcher from Chalmers University of Technology. The author has contributed to research in topics: Track (rail transport) & Ballast. The author has an hindex of 5, co-authored 8 publications receiving 123 citations.

Simulation of track settlement in railway turnouts

Abstract: A methodology for the simulation of track settlement in railway turnouts (switches and crossings, S&C) is presented. The methodology predicts accumulated settlement for a given set of traffic loads using an iterative and cross-disciplinary procedure. The different modules of the procedure include (I) simulation of dynamic vehicle-track interaction in a turnout applying a validated software for multibody vehicle dynamics considering space-dependent track properties, (II) calculation of load distribution and sleeper-ballast contact pressure using a detailed finite element model of a turnout that includes all of the rails (stock rails, switch rails, closure rails, crossing nose, wing rails and check rails), rail pads, baseplates and sleepers on ballast, (III) prediction of track settlement for a given number of load cycles and (IV) calculation of accumulated track settlement at each sleeper and the resulting vertical track irregularity along the turnout which is used as input in the next step of the iteration. The iteration scheme is demonstrated by calculating the track settlement at the crossing when the studied turnout is exposed to freight traffic in the facing move of the through route.

Three-dimensional modelling of differential railway track settlement using a cycle domain constitutive model

Abstract: A method for simulation of differential (spatially varying) track settlement in a ballasted railway track is presented. It employs a cycle domain constitutive model to determine accumulated plastic (permanent) deformation of the granular layers supporting the track. The constitutive model is adopted for both the ballast and the sub-ballast but with different parameter sets. The proposed framework can be used to predict differential track settlement accounting for heterogeneous (space-variant) track characteristics and loading conditions. Here, it is demonstrated for three-dimensional continuum modelling of a railway crossing panel subjected to a large number of axle passages. Because of the design of the crossing panel and the transient character of the impact loads on the crossing, the load transferred into the track bed is not uniform along the track, and the resulting differential settlement leads to vertical irregularities in track geometry. The spatial variation of track settlement is calculated both along the sleepers and along the rails. The influences of the number of adjacent sleepers accounted for in the model and the stiffness of the subgrade on the predicted settlement at the crossing are studied.

Geometry mapping and additional stresses of ballastless track structure caused by subgrade differential settlement under self-weight loads in high-speed railways

Abstract: Rail irregularities caused by subgrade differential settlement will accelerate track degradation and lower ride comfort and safety. Since the track substructure is normally inaccessible, these problems are hard to be detected early. To study the mapping characteristics of deflection profiles in the ballastless track-subgrade system, a 3D FEM model considering the contacts between different layers was established to simulate different settlement scenarios. The numerical results were first validated by the comparisons of rail deflections with a full-scale physical model testing. Then the influences of subgrade differential settlement on the CRTS II type ballastless track were analyzed, including the deflection profiles, additional tensile stresses and contact stresses. The settlement transfer characteristics from the subgrade surface to the rail were revealed, which were largely dependent on the track equivalent flexibility. A unified formula in terms of the settlement amplitude and track equivalent flexibility was proposed to describe the geometry mapping relationship. The scenario of hanging track structure occurred at the subgrade differential settlement with wavelengths shorter than 15 m, or wave-length between 15 m and 20 m and amplitude larger than 15 mm. The thresholds of unacceptable settlement wavelengths for the additional stresses were 10–20 m for the concrete base and 10–15 m for the subgrade with the settlement amplitudes smaller than 15 mm. Differential settlement with shorter wavelengths was more vulnerable, and the critical scenarios of soil yielding at subgrade surface happened earlier than the concrete cracking in the track structure. Subgrade maintenance works, such as settlement restoration and soil improvement, were suggested to be implemented before the wavelength reached 10 m to avoid further development of settlement and potential threats to the track structure.