Netherlands: high-tech fastening for high-speed track ... - Hilti

Magazine Fall/Winter 2005
Engineering
Page 15
Don’t forget, you’re
below sea level
here,” says engineer Harry Kolk
as his eyes follow the light-colored
band of concrete that vanishes into
the horizon. We’re at the site of the
dual-line, high-speed railway being
built between Amsterdam and
the Belgian border, part of it on reclaimed
land now protected by
dikes. Harry Kolk’s gaze returns to
the spot on which he’s standing.
Thick steel dowels project at his
feet: high-tech fastenings for highspeed
track on which trains will
run at up to 330 kilometers per
hour. In a few minutes, the dowels
will disappear under the layer of
concrete poured around the sleepers
on the slab track.
The same day, at a different location
on this band of concrete,
Danny Mangal opens his ears: “I
listen for the signal of course, but
that’s about all there is to it,” he
says. The signal, indicating the position
of a rebar in the concrete, is
emitted by the Hilti Ferroscan detector.
“Meet a good friend of
mine,” says Danny, pointing to the
Hilti Ferroscan unit. His workmates,
using a template, have
marked out the projected positions
of the steel dowels on the strip of
non-woven fabric, a so-called geotextile,
covering the concrete substructure.
Danny Mangal runs the
Hilti Ferroscan detector along the
geotextile to ensure that the positions
of the holes for the dowels
don’t coincide with the steel reinforcing
bars in the concrete below.
Also on the same day, Peter
Schaap, the man responsible for all
of the work being carried out,
strides into his temporary site office.
His tousled hair gives him the
look of someone who has just
Peter Schaap: “Each construction
team must complete
300 meters every day.”
leaned out the window of a fastmoving
train. “We’re setting about
750 dowels a day, and each construction
team has to complete a
stretch of 300 meters every day.”
The south stretch of the track between
Rotterdam and the Belgian
border has to be completed by
April 2006 and the north stretch
from Amsterdam to Rotterdam six
months later. After testing, the
trains will go into scheduled service
on the total of 90 kilometers of
track a year after the completion
date.
Flashback to the Hilti
Research Center in
Liechtenstein, Christmas
2003: down in the cellar, powerful
hydraulic units are running day and
night, generating a hydraulic pressure
of up to 280 bar that applies a
shear force of 33 kilonewtons and
simulated tensile stress ten million
times to each of the dowels on the
test rigs in 4 tests running simultaneously.
You can read more about
the tests on page 20.
The solution with the dowels was
developed toward the end of the
summer of 2003 by a team of Hilti
consultants and research engineers
who specialize in shear connection
and the construction of slab track
rail systems. The system calls for
nine round stainless steel dowels to
be set in the center section of each
of the 6.4-meter concrete slabs that
form the superstructure of the
track. These dowels will take up
the high dynamic forces generated
by the high-speed trains in transverse
and longitudinal directions,
without displacement, and transfer
them to the solid substructure. The
type of steel chosen by the Hilti
specialists remains their secret but
it has been made clear that the tensile
yield strength of A4 stainless
steel would not have been adequate
for the purpose. With a view to preventing
direct contact between the
superstructure and substructure,
already separated by the geotextile,
the Hilti engineers wrapped
the upper sections of the round
bars in a thin plastic foil.
As temperature fluctuations cause
expansion and contraction of the
concrete slabs of the superstructure,
provision was made for an expansion
joint with a width of 10
centimeters between each of the
slabs. The dowels at both ends of
the concrete slab have also been
designed to allow longitudinal expansion.
At the same time, these
dowels are also required to take up
high dynamic loads, although only
in a transverse direction. The Hilti
engineers proposed use of a round
bar, the upper part of which has
two flat surfaces, like a bar that has
been squashed from both sides.
The lateral forces act on these flat
areas. To ensure correct behavior
of the dowels under the influence
Switch to dowels
Civil engineering works such as
bridges or viaducts have their
own set of rules when it comes to
behavior under dynamic loading.
Slab track railway substructures
were originally cast in concrete in
the form of a trough. The trough’s
side walls took up transverse
forces. Later, a ridge-like hump in
the center part of the substructure,
known as a corbel, took over
from the trough design.
As a result of being built on piles,
the characteristics of this highspeed
rail track substructure in
the Netherlands can be compared
to those of a bridge. Accordingly,
the engineers were required
to even further optimize
the dynamic behavior of the superstructure
relative to the statically
fixed load-bearing substructure
layer, the settlementfree
plates. “We therefore had to
adapt the Rheda 2000 system by
making use of segmented short
slabs individually designed for
each settlement-free plate,” explained
Detlef Obieray, Deputy
Project Manager with Rheda
2000 vof, the Infraspeed subcontractor
responsible for constructing
the track. A corbel was
out of the question as the substructure
with a thickness of 70
centimeters had already been
completed. As the thickness of
the superstructure could not exceed
24 centimeters, the depth
of coverage over the corbel
would not have been adequate in
any case. Hilti devised the solution
with the Hilti HCD-C and
HCD-O concrete dowels specially
for this project.