Train vibrations and site effect estimation Using ambient vibration measurement to estimate amplification of vibrations from trains

Examensarbete för masterexamen

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Type: Examensarbete för masterexamen
Master Thesis
Title: Train vibrations and site effect estimation Using ambient vibration measurement to estimate amplification of vibrations from trains
Authors: Arén Frid, Gustaf
Abstract: Train induced vibrations are known to cause annoyance and sleeping disorders among people living close to rail roads. This and other problems arising around train vibrations are brought up to date as the current government as well as previous ones suggest building of high speed train routes. The methods, commonly used in Sweden, for predicting levels of train induced vibrations are semi-empirical meaning that a formula is used in which site specific constants require measurements at the site to determine their value. This thesis aims to study amplification of vibrations whose source are trainpassages. Specifically the fundamental frequency, having a wavelength corresponding to four times the soil depth is subject for the analysis. A method frequently used by seismologists to estimate amplification of earth quakes at certain sites is used. By measuring ambient vibrations with a three-axial accelerometer or geophone and dividing the mean of the two spectra of the horisontal components by that of the vertical,the fundamental frequency, f0, will be indicated by a peak in the resulting spectrum, called the H/V ratio. The method can also, to some extent, estimate the amplification factor at f0. The effect of f0 on train vibration is studied in three steps. In the first step, measurement results from previous studies are studied with regard to f0, derived from soil depth maps and estimated deformation parameters. For the next step, FEM calculations are carried out studying transfer functions at the surface of a soil deposit with soil depth as parameter. Material parameters are chosen so that the fundamental frequency should appear within the studied frequency range. Also,measurements are performed using the H/V-ratio technique. At a meadow adjacent to a rail road, ambient vibrations are measured as well as vibrations from trains passing by close to and further away from the rail in order to obtain a transfer function. The spectra obtained from the train passages at each point, as well as the transfer functions, are compared with the corresponding H/V-ratio to see if there is amplification at f0. The results from the literature study indicate that f0 does play a role in that sense that wave propagation below that frequency cannot occur,theoretically. The study of previously made measurements confirms this as sites with a high estimated f0 are not subject to high vibration levels. The FEM calculations also show a dependency of transmitted wave energy on soil depth in that sense that there is a frequency below which there is very weak wave propagation. The response spectra at 10 m and 40 m as well as the transfer function from the source to the field point also inherit a peak at this frequency which is one third octave lower than the expected fundamental frequency, concerning the vertical component. As for the measurements, no conclusions can be made as the measurement equipment used was not sensitive enough to capture ambience. Nevertheless, the peaks in the H/V-ratio, although weak, appear at the same frequencies as those at which amplification occur in the measurement of train passages. It cannot be concluded, but also not excluded, that the difference in the measured spectra at the different points depend on f0.
Keywords: Building Futures;Akustik;Building Futures;Acoustics
Issue Date: 2019
Publisher: Chalmers tekniska högskola / Institutionen för arkitektur och samhällsbyggnadsteknik
Chalmers University of Technology / Department of Architecture and Civil Engineering
Collection:Examensarbeten för masterexamen // Master Theses

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