The tunnel will be driven downwards from the Reppisch
Valley excavation site under the Uetliberg through to the Zurich-South
interchange in the Brunau area (SG-DIE, MO-UET).
Gjuch, Diebis and Juchegg soft ground sections
All the soft ground sections are being driven using the core construction method. The excavation support in the soft ground sections consist of steel arches (HEM 180 girders spaced 1 m apart) and 25 cm thick steel fiber reinforced shotcrete.
Some large-scale support measures will be necessary to cut through these ground conditions which, in geotechnical terms, are extremely difficult (injection, water table lowering, preliminary drainage bores etc.).
Dividing of soft ground cross-sections
The molasse sections
The Eichholz molasse section will be excavated in the extension of the Gjuch soft ground section. The crown of the tunnel will be driven by drill and blast, core, left and right side walls and base are excavated by ripping. The standard rock support is generally mesh-reinforced shotcrete and rock bolts.
In critical areas, particularly in the section driven under the SBB-Landikon tunnel, steel supports have been specified.
In the Uetliberg molasse section, the tunnel
is being excavated using a tunnel boring machine (5.0 m diameter) followed
by a tunnel bore extender (TBE) which applies undercutting techniques.
|The sealing, the base, the service duct (prefabricated elements) and back fill on the sides will be installed from the back-up equipment.|
|The lining and the intermediate ceiling will be installed in stages in the rear.|