A joint venture was awarded a contract to construct a 35 km section of a new 89 km railway line between Nuremberg and Ingolstadt in Germany. The project includes six major railway bridges totaling 932 m in length, 26 minor railway bridges, 11 road bridges, and two tunnels. One of the tunnels is the 1,340m long Offenbau Tunnel, which is being constructed using a sophisticated "lid-cover" method under compressed air due to the presence of underground water that prevented traditional cut-and-cover excavation. 70,000m of bored piles were installed to form the tunnel walls, which support a 1.3m thick concrete roof. Excavation beneath the roof is performed under

1. A joint venture under the techni-
cal management of Bilfinger
Berger AG was awarded the
contract for the construction of a
35 km long section of the 89 km
long new railway line between
Nuremberg and Ingolstadt. The
works include six major railway
bridges with a total length of 932
m, 26 minor railway bridges, 11
road bridges and two tunnels.
One of the tunnels is the 1,340
m long Offenbau Tunnel with a
cross-section of 12.3 m x 7.5 m.
It is situated 45 km south of
Nuremberg and has to be built
to protect the nearby village of
Offenbau against noise from the
new high-speed railway line.
Originally, the tunnel was to be
built using the cut-and-cover
method, but it turned out that
artesian water in the ground did
not permit the required excava-
tion down to nearly 20 m. In-
stead, the more sophisticated
lid-cover method under com-
pressed air is now being applied
for the construction of the tunnel.
The two tunnel walls consist of
overlapping bored piles. They
carry a 1.3 m thick concrete
cover which is to form the tunnel
roof. The soil which was previ-
ously excavated to enable the
construction of the concrete
cover, was backfilled on top of
the concrete cover, forming a 2-
6 m thick layer. The pile walls
consist of piles with a diameter
of 1.2 m installed at distances of
1.04 m. 70,000 m of borings
were made using 12 drilling rigs.
Soil excavation beneath the
tunnel roof is performed under
excess pressure of 1.0 bar.
Three separate locks were in-
stalled at the southern portal for
persons, material and large
equipment. Excavation is made
using electrically-powered
equipment and the material is
transported by means of electri-
cally driven trains.
The bottom of the excavation is
secured by a 0.3 m thick shot-
crete layer, vaulted downwards
and anchored to the bored pile
wall. After completion of the
works under compressed air
and prior to the installation of the
bottom slab, it will protect the
bottom of the excavation against
uplift. The bottom slab and the
inner lining of the tunnel will be
concreted under atmospheric
pressure.
Offenbau Tunnel
High-Speed Railway
Line Nuremberg-
Ingolstadt,
Germany
Contract Value:
USD (m) 160.9
Construction Period:
04/2002 – 09/2006
Client:
Deutsche Bahn AG
Services:
Construction of a 1,340 m
long tunnel under
compressed air
Reg.41-bb-000-28.1.712-00