Keywords: microtremor, railway traffic effects on structures, prediction, dynamic half space models, structure response models, in situ experimental tests, ground vibration, structure response spectra, spectral analysis.

A numerical-experimental model for the calculation of ground-borne vibrations arising from railway traffic is introduced. The calculation procedures for the free-field dynamic response at a distant point (from the railway track) using spectral analysis with experimental input data are described. In the numerical model the soils are modelled as a viscoelastic half-space [1,2].

In the numerical-experimental model (NEM) experimentally measured soil vibration data near the railway track is used as an input data into viscoelastic halfspace. The free-field vibration at the distance prediction is calculated using a spectral analysis procedure. In this model procedure, it is suggested that a soil medium transfer function, elastic and attenuation soil parameters from the experimental in situ test (impact-seismic method - ISM) are applied. Then the half-space output data (output PSD) at a distance are calculated using the standard spectral analysis procedure [3]. The use of the random process theory to predict the level of ground vibration in the vicinity of railways using the calculation of the spectrum of vibration at a half-space point are possible by using two principal ways: (i) using a computer implementation of the theoretical expression for the rail roughness spectrum, the vehicle mass distribution spectrum and a model of vehicle dynamics and track-soil interaction and the frequency response function (FRF) of the ground by a method involving integral transform, (ii) using an average response force spectrum derived from experimental data for the authorized railway category with a corresponding track profile and the frequency response function of the ground and to calculate the response spectrum vibration at a point in the same way as mentioned in (i). The random process theory in the investigation of the dynamic ground properties can be utilized as well. Using the input signal (due to traffic) the measurement in the ground and the output signal measurement passing through the ground, frequency response function, elastic and attenuation characteristics of the ground can be obtained [1]. To provide a case study of the ground vibration and the transmission from a railway the experimental tests were carried out adjacent to the ZSR railway Bratislava - Vienna track No. 1. The ground vibration frequencies were obtained using spectral analysis of the recorded soil response dynamic components, which are considered ergodic and stationary. Spectral analysis was performed using the software package NI LabVIEW.

1

J. Bencat, et al., "Microtremor due to Traffic", Research report A-4-92/b, UTC Zilina, SK, 1992. (in Slovak)

2

P. Broeck, G. Roeck, "The vertical receptance of track including soil-structure interaction", in "Eurodyn 99", Prague, CR, A.A. Balkema, 849-853, 1999.

3

J.S. Bendat, A.G. Piersol, "Engineering Applications of Correlation and Spectral Analysis", Wiley & Sons, New York, 1993.

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