Special features in tendering, award and contract - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 348

tunnel. The maximum overburden is 200 m. The tunnel also passes below the active two-track
Brandleite rail tunnel. Safety requirements demand the provision of stopping bays every 700 m
and the two bores are also connected every 350 m by escape tunnels.
The tender design intended the use of shotcrete tunnelling. Only shortly before the com-
pletion of the tender documents were a few conditions included for an alternative proposal
using a shield machine.
Quote from the tender documents: “Under the given geotechnical conditions, the use of
a shielded tunnel boring machine (TBM-S) is fundamentally possible. The construction
process can be tendered as an alternative as long as bulk material handling is considered.”
The tender documents contain brief details applicable to alternative proposals concerning
construction process concept, machine concept, segment lining, material handling and
transport concept.
The Rennsteig Tunnel was awarded as a shotcrete tunnel, since this turned out to be cheap-
er than mechanised tunnelling, which led to tenders about 10 % more expensive.
Meanwhile the first experience of constructing this tunnel is available. The geological
conditions would have been suitable for a machine along about half of the tunnel length.
The rock mass classes are often more advantageous than forecast and the water ingress
is much less. According to experience in Switzerland, a TBM could have achieved much
faster advance rates.
Lainzer Tunnel. The Lainzer Tunnel connects the Westbahn, Südbahn and Donauländer-
bahn lines in the city area of Vienna with a total length of about 5.5 km. The project is
divided into the Hetzendorf Tunnel with a length of about 2 km and the Lainz Tunnel
about 3.5 km long, of which 0.3 km is supported with shotcrete (Fig. 9-7). The diameter
of the two-track tunnel is 13.8 m.
Figure 9-7 Geological profile of the Hetzendorf and Lainzer Tunnels.