Official launch of the first of Herrenknecht’s two TBMs on the Finnetunnel twin rail link project in Germany was marked at the close of last month – slightly ahead of programme.

The start-up of the 10.82m diameter convertible, mixed mode machine by the Wayss & Freytag-led JV will be followed shortly by its sister TBM. The first shield was initially due to commence excavation in July, the second TBM in December.

The machines will bore 4,600m lengths of tunnel with the rest of the 6.8km long drives constructed using the NATM technique.

Geology along the alignment comprises high groundwater head (up to 6 bar) where borehole drawdown will be used to enable the TBMs, in the latter part of the drives, to bore those sections in open mode. But, due to weathered sandstone with clay/silt, the groundwater cannot be lowered in the early stretch and the TBMs will operate in slurry mode.

Tunnel lining consists of 9.6m i.d. segmental rings (6+1), the rings being 2m long. Cross passages with airlocks are to be built every 100m.

The JV was awarded a US$381M contract, with other consortium members including Max Bogl and two units of Porr.

Finnetunnel is being built as a key section of the 10.5km long Erfurt to Leipzig/Halle twin track rail line.

The client, DB Netz, awarded the contract in late 2006 and the link is due for completion in 2011 (T&TI, September 2007, p10).

Official launch of the first of two TBMs for the Finnetunnel