Digital Issue 2010 trial preview 150 dpi

Contrary to expectation, an immersed tube across the 20km Fehmarnbelt between
Denmark and Germany has come in a whisker less than a cable-stayed bridge.
Technical risks, long term environmental impacts, navigational safety and developments
toward more carbon efficient transportation played a large part in reducing the
estimated cost of the undersea alternative and elevated it to the preferred solution.
The numbers are in and the tunnel
has it by a nose! As large as the
numbers are for the scope of the
project, a cable-stayed bridge across
the Fehmarnbelt for a fixed connection
between Denmark and Germany comes
in at DKK 38.5 billion (about US$7 billion
or E5 billion) while the estimate for an
immersed tube across the 20km strait is
just slightly less at DKK 37.9 billion.
After agreeing the fixed link concept
in September 2008, two teams in the
Danish owner organisation, Femern A/S,
developed conceptual designs and cost
estimates for a four-lane highway and twotrack
railway connection across the sea on
a cable-stayed bridge and in an immersed
tube tunnel. Of these, the bridge had
been considered the less expensive option
through the process and therefore the
favoured plan. Announcement of the cost
estimates in November 2010 produced
a surprise result with the immersed tube
revealing a lower estimate than the bridge.
The result illustrates the tremendous
work achieved by the tunnel team in
exploring new concepts to reduce the
Tunnel beats bridge for
Fehmarnbelt Fixed Link
cost of building, operating and maintaining
an undersea link. Changing attitudes and
new techniques for reducing polluting
substances into the atmosphere also
played a role in the outcome.
One of the most significant cost savings
was elimination of an intermediate manmade
island designed to accommodate a
ventilation shaft and equipment installation.
Projections of low traffic volumes in the
initial years, together with significant and
rapid technical advances in reducing toxic
emissions by road vehicles, have allowed
the adoption of longitudinal ventilation in
the long four-lane traffic tunnel. Instead
of large ventilation buildings and the
intermediate vent station island, fans will
be installed in ceiling recesses at 400m
intervals along the 20km link. This also
optimizes the design of the tunnel’s cross
section eliminating the need for separate
transverse or semi-transverse ventilation
ducts. “The change reduces the volume of
concrete in the immersed tube elements by
some 10%, which is a significant saving on
a project of this scale,” said Steen Lykke,
Project Director Tunnel for Femern A/S.
TunnelTalk reporting
Since release of the cost comparisons
in November 2010, Danish politicians
have adopted the immersed tunnel
as the preferred option. “The decision
means that Femern A/S has reached an
important milestone,” said Leo Larsen,
CEO, Femern A/S. “As our conceptual
design projects are based on a thorough
technical foundation, we can now focus on
ensuring that the authorities approve the
project, including from an environmental
perspective.”
Making the case
Fewer risks, all told, in both the
construction and operational phases than
a cable-stayed bridge is how leaders of the
project say they arrived at recommending
the immersed tunnel.
A cable-stayed bridge across the
Fehmarnbelt, with two free spans of 724m
each, would be the largest spans ever
constructed for either road or rail traffic.
Compounded by the high shipping traffic
in the area, this would pose significant risks
in the construction phase in terms of cost
overruns, delays and industrial accidents.
PREVIEW
Immersed tube tunnel (left) comes in slightly less costly and considered less risky over all than the cable-stayed bridge alternative (right)
MEGA PROJECTS
www.TunnelTalk.com TunnelTalk ANNUAL REVIEW 2010
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