In previous in-situ measurements of metro trains it has been found that the velocity level on the track or tunnel wall may vary significantly between different train passages, even though the measuring section, the type of trains and the track and tunnel conditions are identical. An investigation is carried out into the sources of this variability, using a 3D train-track numerical model. This is built using the software SIMPACK and ABAQUS, and is connected through one-way coupling to a finite element model of the tunnel and soil. These models are used to study the influence of various train parameters, including the wheel and rail unevenness, train speed and degree of train loading. For comparison, in-situ measurements were made of the dynamic response of the rail and tunnel wall. The rail roughness at the site as well as the wheel unevenness of all 48 wheels for one train were measured. The results from the model indicate that the wheel unevenness affects the rail velocity level in the frequency region between 25 and 250 Hz and tunnel wall vibration above 5 Hz. The rail velocity level can vary by up to 20 dB due to wheel unevenness, with the largest variations occurring in the frequency bands 50–63 Hz. Variations in passenger loading affect the train-induced vibration by up to 4.5 dB, mainly in the low frequency region. When the train speed varies within a range of ±20% relative to the nominal speed 60 km/h, the frequencies of the peaks are shifted and the level in some frequency bands can change by as much as 10 dB. However, the largest influence is that of the wheel unevenness. It is concluded that the variation in these parameters, especially the wheel and rail unevenness, should be considered to achieve reliable predictions of train-induced vibration.
Despite the fact railways are seen as an environmentally friendly and sustainable form of transport, however, the train-induced vibration has been seen as a negative environmental consequence. The ballasted ladder track is one type of ballasted track with longitudinal sleepers. The elastic elements can not only protect the track structure but also control the vibration. To investigate the vibration mitigation effects of ballasted ladder track with elastic elements, a finite element - infinite element (FE-IFE) model was built considering the elastic elements of under-sleeper pads (USPs) and under-ballast mats (UBMs). This model was validated by a laboratory test. Then, the moving train load was obtained based on the multi-body dynamics (MBD)-finite elements method (FEM) analysis. The vibration mitigation effects of the ballasted ladder track with different types of elastic elements were calculated compared with the ballasted tracks without elastic elements. The results indicate that: (1) the ballasted ladder track has the advantage of vibration reduction at low frequencies, with a maximum vibration attenuation of 25.2 dB and an averaged vibration attenuation of 19.0 dB between 5 and 20 Hz through the ballast. (2) The ballasted ladder track with USPs or UBMs can provide better vibration attenuation between 30 and 100 Hz, but it induces a vibration amplification between 5 and 30 Hz. (3) The ballasted ladder track with elastic elements in different cases can provide different vibration mitigation effects. The ballasted ladder track with both USPs and UBMs can provide the best mitigation effect with an average vibration mitigation of approximately 15 dB and a maximum vibration mitigation of 30 dB between 30 and 100 Hz.
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