Rail conquers the Alps

42 January 2015 | Railway Gazette International
TRACK Low-vibration
main requirements were durability and
a long service life, given the anticipated
loading of 0·5 million tonnes per day
with a maximum axleload of 25 tonnes.
The sleeper blocks for the GBT project
were manufactured by European LVT
licensee Vigier Rail Ltd using a new production
process based on the use of selfcompacting
concrete. An increased level
of automation offered a consistently high
quality, along with guaranteed traceability
of all the components and materials
used. It was also possible to increase the
geometric accuracy, thanks to the use of
high-precision moulds. As each support
can be ‘cloned’, a one-for-one replacement
becomes more feasible, which may
prove necessary to rectify any damage
from a derailment or objects falling onto
the track, for example.
An essential part of the test programme
was the cyclic load tests, which
were carried out at the Institute of
Road, Railway & Airfield Construction
in München. Sample track components
were subjected to more than
10 million load cycles, under conditions
which simulated the ambient tunnel
temperature.
The static and dynamic (1 to 15 Hz)
system modulus of rigidity was first
determined, using ‘new’ specimens installed
at inclinations of 0° and 22°. The
dynamic fatigue test was then carried
out to 10 million cycles, with a load application
angle of 22° and a temperature
of 40°C to simulate the worst-case conditions.
The system rigidity moduli were
determined again, so that the ‘before’
and ‘after’ values could be compared.
The test specimens exhibited support
point spring rates between 28·4 kN/mm
(vertical load, static) and 50·0 kN/mm
(-22° load, dynamic). As regards the dynamic
demands, both specimens demonstrated
a stiffening of approximately
30%, which did not increase much further
at a loading frequency greater than
5 Hz. This met the requirements of
The LVT HA
trackform was
used for the Zürich
Durchmesserlinie
to minimise ground
vibration in an urban
area.
Fig 4. Average value
of maximum rail
deflection under
locomotive axles at
different speeds.
project promoter Alptransit Gotthard,
which specified a static rigidity of greater
than 25·0 kN/mm with a horizontal
inclination and a dynamic rigidity of
less than 55·0 kN/mm with an inclined
installation.
During the dynamic fatigue test, both
specimens were tested simultaneously.
Once the required temperature of 40°C
between the block pad and the bottom
of the concrete block had been reached,
10 million load cycles were applied
with a vertical load component impact
of 60 kN per support. One criterion in
the tender specifications was that the
amplitude or the change in displacement
amplitude should be less than
20% between 100 and 10 million load
cycles. The other was that the support
points should not wear through, and the
boot must not show wear of more than
50% of the wall thickness at any point.
Examination of the specimens showed
that both criteria had been met. A visual
examination of the track system components
after 10 million load cycles revealed
only slight signs of wear, which it
was concluded were due to the effect of
initial adjustments or possible restraints.
With construction well advanced, the
contractors also undertook practical dynamic
deflection measurements in February
and March 2014, using the 13 km
long Faido – Bodio test section in the
western bore of the tunnel. On February
20-21, the deflection was measured
under a Class Re420 electric locomotive
running at speeds of 10, 80 and
120 km/h. On March 11-13 tests were
undertaken using a pair of Class Re460
locomotives and four coaches, running
at 160, 180, 200 and 220 km/h. These
last runs were also being used to test the
traction current supply at the same time.
The measurements were taken close
to cross-passage 150, which lies about
half-way along the test section. The
same instrumentation arrangement was
used as for the laboratory tests, with
Maximum rail deflection mm
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inductive displacement transducers on
the left and right rails at three crosssections
(Fig 2). Measurements were
taken automatically during both sets of
trials and also monitored and recorded
at a base in the village of Biasca via a
network link.
Fig 3 shows the measured rail deflections
from a test at 220 km/h at measurement
cross-section 2. A 100 Hz
low-pass filter was used to analyse the
signals. Fig 4 shows the average value of
the maximum rail deflection under the
locomotive axles for the trial runs at the
various speed levels.
In summary, the rail deflection at
the measured support points remained
virtually the same, at approximately
1·3 mm for both quasi-static and dynamic
loading. The deeper deflections
measured at speeds of 80 km/h and
120 km/h can be attributed to the dynamic
influences of the loading vehicle,
which have a greater effect on the
deflection curve than the stiffening of
the elastic material. A stiffening of 1·3
which was determined during the laboratory
trials in 2010 was not significantly
exceeded during the practical testing.
Given that in the LVT track structure
it is mainly the deformation of the
elastic block pad that contributes to
rail deflection and support rigidity, the
dynamic behaviour of the system as a
whole corresponds to the behaviour of
the block pads 8 .
Installation methodology
The tracklaying process for the
Gotthard Base Tunnel was described
in detail in RG 7.11 p44. Awarded
the tracklaying contract in 2008, the
ARGE Fahrbahn Transtec Gotthard
consortium of Balfour Beatty Rail and
Renaissance Construction brought
together a team of trackwork specialists
with international experience. The
consortium developed an installation
methodology that guaranteed very high
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Speed km/h