Subgrade vibrations and long-term stability of an embankment-bridge transition zone in non-ballasted high-speed railway

The current major issue of the large-scale high-speed railway networks worldwide is to maintain their long-term safe and stable operations. The sudden changes in track supporting condition in transition zones inevitably lead to deterioration under long-term high-speed train loads. Aiming at studying the long-term performance of subgrade vibrations and dynamic stability, two vibration response tests were conducted in an embankment-bridge transition of a non-ballasted high-speed railway in China, with a time interval of 32 months. The frequency spectrum characteristics and vibration amplitudes of the two tests were comparatively analyzed. Additionally, field test results were used to determine the dynamic shear strains of the subgrade for the evaluation of long-term dynamic stability. The findings indicate that the influence of the abutment weakens as the distance from the abutment increases, thus subgrade vibration amplitudes show an increasing trend and the dominant frequencies shift towards the lower frequency range. The influence range of the abutment is at least 25.54 m. After 32 months of commercial operation, there has been slight changes in the variations of subgrade vibration amplitudes and vibration spectrum along the longitudinal direction. The dominant frequencies in the vicinity of the abutment have shifted towards the lower frequency range, and the longitudinal variation of vibration amplitudes has become gentler. Further based on the obtained maximum dynamic shear strain of the subgrade, which remains below the threshold limits, it can be comprehensively concluded that the long-term dynamic stability of the test site meets the requirement for high-speed train operation.