The influence of various excitation mechanisms on ground vibration from trains

Abstract

Ground vibration from trains is an increasingly important environmental problem. This study investigates the various excitation mechanisms of ground vibration. An existing semi-analytical model, TGV, which considers both the quasi-static excitation due to moving axle loads and the dynamic excitation due to vertical rail irregularities, has been validated by an extensive measurement campaign. This involved the determination of soil properties at two sites with soft clay soil. These were found to exhibit an inversion of the wave speed profile. Good agreement was found between measurements and predictions of vibration due to train pass-bys.

The relative importance of the dynamic and quasi-static excitation mechanisms has been investigated for a range of conditions including changes to track and vehicle parameters. The dynamic excitation mechanism is found to dominate the results above about 10 Hz and at all frequencies for distances beyond 10 m from the track. In order to study other excitation mechanisms a new hybrid model has been developed. This combines a wheel/track interaction model working in the time-spatial domain and an axisymmetric layered ground model working in the wave number-frequency domain. In the time domain model a ‘circular’ track is introduced to allow longer responses to be calculated. The model is then validated by comparison with the existing TGV model. A reasonable agreement is found.

The hybrid model has then been used to investigate the relative importance of quasi-static loads, dynamic loads and some other excitation mechanisms for trains running on the ground. The sleeper-passing effect is investigated for both constant and variable sleeper spacing but it is found to give much lower responses than those due to roughness. Variable ballast stiffness is also investigated and found not to be significant. Impact forces caused by the passage of wheels over dipped welds and stepped joints are found to generate ground responses that are considerably larger than roughness excitation in the region close to these track defects. However the response decays more rapidly with distance than that due to roughness.

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Identifiers

ORCID for David J. Thompson: orcid.org/0000-0002-7964-5906

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