Keywords: high speed railways, train induced vibrations, numerical modelling, finite element method, boundary conditions, parametric study.

One of the environmental issues arising from the installation of high speed railways refers to train induced vibrations, since the waves propagating through the soil mass may interact with the adjacent buildings and construction, hence potentially causing structural damage, malfunctioning of specific sensitive devices or equipment and discomfort to people.

In this context, the development of methodologies for the analysis and prediction of high speed train induced vibrations is particularly interesting, in order to identify, as early as in the design stage, the zones where problems are most likely to occur, and to enable a well-timed study of the most adequate solutions for its mitigation.

Among the several numerical methods available for the study of wave propagation problems, the finite element method (FEM) has proven to be very suitable since, given its great versatility, it enables to analyse complex problems. General aspects of modelling based on the FEM are discussed in this paper, as well as the application of viscous dampers in the simulation of the transparency conditions at the boundaries.

In this study an application of a simplified numerical analysis methodology was made to the study of induced vibrations in the vicinity of a railway track by the passage of the high speed train at different speeds. The methodology is based on a longitudinal two-dimensional model which enables to obtain the vertical displacement at a certain section of the track, which were at a second stage imposed on a perpendicular two-dimensional model, perpendicular to the track at that section. This model includes, besides the track and the soil, two buildings in the vicinity of the track.

The application aims to study the following factors that may influence train induced vibrations: circulation speed, distance to the track, soil properties and bedrock location. To evaluate the influence of the soil properties, three different values of the Young's modulus of the soil were considered. To analyse the influence of the bedrock position, two possibilities for its depth were assumed. This study is based on the evaluation of the vibration velocity for points: i) in the ground at different distances to the track; ii) in the buildings, located at different heights.

The studies performed enabled a general decrease in the rms values of velocity with an increase of the distance to the track to be identified. It was also possible to conclude that rms values in the points at the surface of the ground increase with the decrease of the Young's modulus value, this was more evident for the points near the track. The differences are higher when the value of Young's modulus is reduced from 100 MPa to 50 MPa and they increase with the augment of the speed. The same observations are applicable for the points in the building near the track. It was verified that rms values are slightly higher when the bedrock is located at a smaller depth.

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