Rail conquers the Alps

Railway Gazette International | January 2015 41
Low-vibration TRACK
The LVT support
blocks on one track
in the Heitersberg
tunnel (right) were
renewed in 2014
using a series of
short possessions.
Switzerland’s north-south transit corridors.
Following on from the SBB developments,
BLS also decided to specify
LVT for the 53 km of track, which like
the Gotthard Base Tunnel has been designed
for a line speed of 250 km/h.
In this case, the LVT trackform was
equipped with rubber boots that allow
improved vertical deflection of the individual
blocks, as well as under-block
pads made of polyurethane. Together,
these changes contributed to an improvement
in the dynamic behaviour of
the system.
when the twin-block sleepers on one
of the two tracks were replaced in a series
of overnight possessions. Working
in 100 m sections, the old twin-block
sleepers, including the elastic components,
were replaced by new B12 blocks
with the W14 rail fastenings specially
developed for the relaying project. At
the same time, the SBB IV rail profile
was replaced by SBB VI (UIC60) 7 .
After the sleeper blocks had been
changed on each track length, the line
was put back into operation at the normal
operating speed of 140 km/h. No
subsequent track geometry corrections
or concreting work had to be carried
out.
The so-called ‘Bötzberg system’ has
been gradually refined over time. The
first step was the removal of the crossties
from the twin-block sleepers in the
track at Zürich airport, with the objective
of improving the protection against
vibrations; this modified version was
also adopted for the Zürich S-Bahn
projects 4 .
In the meantime, Sonneville International
had been further developing the
low-vibration track system with individual
blocks. This had been adopted for
the Channel Tunnel project, and trials
at the beginning of the 1990s proved
that a substantial improvement could
be achieved in terms of gauge widening
and lateral track geometry stability
by embedding the single support
points up to 50% deeper in the track
slab. In addition, the electrical resistance
was improved by removal of the
metal cross-ties, with major advantages
for the signalling. In platform areas, slab
track without cross-ties was much easier
to clean, and it allowed good access for
inspection by maintenance staff.
Having installed Sonneville LVT on
an 800 m section of the Grauholz Tunnel,
which was commissioned in 1995 5 ,
SBB subsequently decided to use it
throughout the 5 km Zimmerberg tunnel.
Forming part of the NEAT trans-
Alpine corridor, this tunnel was designed
for a line speed of 200 km/h. The
track design is noteworthy, because both
the infill concrete in which the blocks
are embedded and the tunnel invert itself
have no structural reinforcement 6 .
Four years after the Zimmerberg
tunnel opened in 2003, BLS inaugurated
the 35 km Lötschberg Base Tunnel,
which is another integral part of
Right: Fig 1.
Determination of
system rigidity
moduli on a test
specimen inclined
at 22°.
Far right: Fig 2.
Instrumented
track cross-section,
showing the
amplifier, data
recorder and remote
transmitter in the
background.
Below: Fig 3.
Sequence of rail
deflections recorded
at 220 km/h during
tests in the Gotthard
Base Tunnel.
Rail deflection mm
1∙4
1∙2
1∙0
0∙8
0∙6
0∙4
0∙2
0∙0
Track 2-1 2-2
Track 2-3 2-4
Durability testing
Before selecting the final trackform
for the Gotthard Base Tunnel, SBB required
extensive testing of the various
components, to ensure that they could
withstand the predicted stresses in the
tunnel environment, with temperatures
of around 40°C and 70% humidity. The
2 x Re 460 locomotives 3 x EW passenger coaches Driving coach
10∙0 10∙5 11∙0 11∙5 12∙0 12∙5
Time sec