A consequence of high speed rail transportation is the generation of
elevated ground borne vibrations. This thesis presents several original
contributions towards the prediction of these vibrations.
Firstly, a new three dimensional finite element model capable of
vibration prediction was developed. Its main feature was its ability to model
complex track geometries while doing so through a fully coupled vehicle-tracksoil
system. Model output was compared to experimental results obtained
during this thesis and also to independent data sets. It was shown to predict
velocity time histories, vibration frequency spectrums and international
vibration descriptors with high accuracy.
An appraisal of the suitability of a finite difference time domain
modelling approach for railway vibration prediction was also undertaken. This
resulted in the development of a new ‘higher order’ perfectly matched layers
absorbing boundary condition. This condition was found to offer higher
performance in comparison to current alternative absorbing boundary
conditions.
Field work was then undertaken on high speed lines with varying
embankment conditions in Belgium and England. Vibration data was recorded
up to 100m from each track and geophysical investigations were performed to
determine the underlying soil properties. The results were used for numerical
model validation and also to provide new insights into the effect of various
embankment conditions on vibration propagation. It was found that
embankments generate higher frequency excitation in comparison to nonembankment
cases and that cuttings generate higher vibration levels than noncuttings.
Once validated the finite element model was used to provide new
insights into the effect of train speed, embankment constituent materials and
railway track type on vibration levels. It was found that the shape and
magnitude of ground vibration increased rapidly as the train’s speed
approached the Rayleigh wave speed of the underlying soil. It was also found
that ballast, slab and metal tracks produced similar levels of vibration and that
stiffer embankments reduced vibration levels at distances near and far from the
track.
Two vibration mitigation techniques were also explored through
numerical simulation. Firstly, an analysis was undertaken to determine the
ability of a new modified ballast material to actively isolate vibration within the
track structure. Secondly, wave barrier geometries were investigated to
optimise their performance whilst minimising cost. It was found that barrier
depth was the most influential parameter, whereas width had little effect.
Additionally, geometry optimisation was found to result in a 95% cost saving in
comparison to a base case.
Using a vast array of results generated using the previously developed
finite element model, a new empirical prediction model was also developed,
capable of quickly assessing vibration levels across large sections of track.
Unlike currently available empirical models, it was able to account for soil
properties in its calculation and could predict a variety of international
vibration metrics. It was shown to offer increased prediction performance in
comparison to an alternative empirical model