Wirth is assembling a 7.03m diameter gripper TBM in the Alps for a planned start next month on excavation of an almost 3.9km long inclined shaft for the Limberg II hydro project in Austria.
The construction programme calls for the headrace tunnel to be excavated within 10 months through basalt and gneiss with an average UCS of 100MPa, rising to 150MPa in parts. Rock classes expected to be met are Class II to III, except for near the start of the power tunnel drive. The tunnel bore is to be a straight run at a 45° incline.
Excavation on the project had been due to start early June but weather conditions on the approach to, and at, the construction site, which is higher than 2000m above sea level, hindered the programme.
In February, the machine was ready for transport to enable assembly to be undertaken in April, but that work did not start until mid-May, pushing the programme back a month.
Excavation is still planned to take about nine to 10 months, T&TI was told. Tunnel lining for the bore, which will have a minimum excavated diameter of 7m, calls for shotcrete in parts.
Contractor on the project, and the entire scheme, is a JV led by G Hinteregger and includes Porr Tunnelbau.
The JV placed a US$10M order for the TBM, which is a refurbished and overhauled machine for which Wirth has supplied four new segments to the five-part cutterhead, and the drive module.
The new segments enabled Wirth to increase the diameter of the machine from the 6.7m required for its previous job, also a hydro scheme – the Ermenek project in Turkey.
Prior to that the TBM operated also as a 6.7m diameter machine on the North Side Storage sewer project in Sydney, Australia.
The TBM started out life on a tunnel project in German about 10 years ago.
Limberg II is being developed by Verbund-Austrian Hydro Power as an underground pumped storage plant to more than double the capacity of the Kaprun hydro scheme. The project is to be completed by 2012.
