Slab Track Hits The Right Note In Basle

Gerb 31/10/06 09:19 Page 97
Track Technology
Slab Track Hits The
Right Note In Basle
The Swiss city of Basle is using
floating slab track technology
provided by Gerb, Germany, to
protect its favourite concert hall
from vibrations and noise
caused by passing LRVs.
Anitra Green
Regional Editor
THE Steinenberg in Basle is one of
the most heavily-used sections of
the city’s light rail network, with
LRVs passing at intervals of one to two
minutes. Because of the wear and tear on
the rails and the consequent risk of broken
rails, the city council has been aware
for some time that the track on the
Steinenberg and on Theaterstrasse would
have to be totally replaced. At the same
time it decided to install a floating slab
track system at the T-shaped junction of
the two streets to cut noise and vibration,
which has been a problem for the adjacent
concert hall, the Stadtcasino,
for many years.
The acoustics of this protected
building are reputed to
be among the finest in the
world, but enjoyment of concerts
is spoilt and recordings
are impossible because of the
frequent rumblings from passing
LRVs. The problem has become
even more acute in recent
years due to the use of longer
and heavier LRVs with multiple
axles.
Preliminary work started in
January to build a new underground
service tunnel and reroute
utilities to make room for
the new floating slab track and
adjust the alignment of the
tracks at the junction to provide
a wider curve radius. The underground
structure of this area
is complex since there are sections
of the old city wall that
have to be preserved, and part
of the roof of the Birsig tunnel,
which carries a small tributary
of the Rhine, had to be reconstructed.
Work on the main part of job, to remove
the old rails and install the floating slab
track, started on July 4 and took just six
weeks. This was achieved by closing the
entire city centre to light rail traffic and
working seven days a week, with three
shifts round the clock for the first three
weeks, then two shifts. Trams were rerouted
round the city centre and shuttle
buses laid on to provide a replacement
service. The work coincided with the
local school holidays to keep disruption to
the transport system to a minimum.
Soaring Temperatures
Unfortunately it proved to be one of the
hottest summers on record, and the heat
caused several problems, particularly for
the workers and the rails. The new rails
had to be kept cool by spraying them with
water during the day to try to prevent
them expanding too much, and they could
only be laid at night.
Gerb’s basic floating slab track is like a
bridge supported by springs embedded in
a firm base that isolates the rails from the
substructure. The system can be adapted
according to local needs. Rails are fixed to
a concrete slab or ballasted trough which
is isolated from the substructure by individual
elements containing highly elastic
helical steel springs. The springs form an
elastic interface with the slab, effectively
isolating the dynamic forces. The entire
system is 1.64m deep and is built up in
several stages.
In Basle, a total of 750 steel cylinders
were installed to house the steel springs
on the concrete slab that forms the foundation.
Concrete was then poured in four
stages, with the foundations for the rails
being separated from the rest by a layer of
special matting, so that any future work
on the rails can be carried out without affecting
the rest of the structure. After the
necessary adjustments to the system and
test running, normal light rail services
were expected to resume punctually
ready for the new school term beginning
on August 14.
The springs are designed to last 25
years, which is about the same time as the
new rails. Unfortunately, because of space
limitations, visual examination of the
spring elements is not possible, so it is
Installation of the floating slab track underway in the Steinenberg looking towards the junction with
Theaterstrasse which branches off to the right.
Reprinted from the September 2006 issue of International Railway Journal

Gerb 31/10/06 09:19 Page 98
Flat elastomer
sealing strip
Surfacing
Hot mixed
aggregates
Track Technology
Filler stabilised
with concrete
Wall element
prefabricated
Poured on site
(connecting
reinforcement out
of base plates)
proposed to dismantle some of them from
time to time to monitor their efficiency.
With these measures, the noise in the
concert hall should be reduced by 20-
25dB, which will bring it down to a level
experts say is acceptable. The previous
level was around 46dB. The authorities in
Basle selected this option as being the
Spring elements
cross-section
Asphalt
GERB spring elements
GSI -R2
GERB’S FLOATING SLAB TRACK
Air shaft
Foil as separating layer
best system available today. The alternative
would have been a simpler system
only 900mm deep, which although
cheaper would only have reduced noise
levels by 10 to 15dB.
Basle city council approved expenditure
of SFr 11.8 million ($US 9.7 million)
for the project. Of this, SFr 4.7 million was
Rail chairs and recesses
cross-section
for preliminary work on the Steinenberg,
and SFr 7.1 million for the installation of
the floating slab track. Another SFr 8 million
is being spent on related works. SFr 3
million is being contributed by a speciallyformed
private foundation. The entire
project is scheduled for completion by
February 2007. IRJ
Reprinted from the September 2006 issue of International Railway Journal
Air shaft