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

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 wavelength 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.