Analysis of Metro Track Irregularity Performance under Different track bed Conditions

［Objective］ With the increase in metro operating speeds and density, the deterioration rate of metro track regularity accelerates due to dynamic disturbance in train vehicles. It is therefore necessary to analyze and understand the actual service performance of track irregularities under different track bed conditions to support maintenance operations for metro track systems. ［Method］ To compare the differences in track irregularity performance under various track bed types, evaluation is carried out using time-domain methods (amplitude, mean value, peak value, and TQI-track quality index), frequency-domain track irregularity spectra, and fractal dimension. These methods are applied to assess the advantages and disadvantages of track bed types including ballast, monolithic slab, and supported-block rail-bearing type track bed systems. ［Result & Conclusion］ In the time domain, based on a comprehensive comparison of amplitude, mean value, and peak value calculation results, the mondithic slad type demonstrates the best vertical track regularity before and after the rail installation, followed by the bearing slab type, with ballast type performing the worst. In terms of track alignment irregularity, the three ballast structures show no significant differences. However, TQI results reveals that monolithic slab type exhibits significantly superior whole track regularity quality over the other two. In the frequency domain, when compared to international track spectra, all track bed types in China display similar distribution patterns in the medium-wavelength range but outperforms foreign systems in the long-wavelength range. From a fractal characteristics perspective, the integral poured ballast shows the best overall performance. On the fractal dimension of three wavelengths, the medium and short wavelength components of the track display more significant variations, while the long-wavelength distribution remains relatively stable with minor changes.