Skanska's record raise bore

Skanska Raise Boring is claiming a Scandinavian record for its 5m diameter raisebore carried out for a penstock shaft at the Follafoss hydropower plant near Trondheim in Norway.

The US$274,382 bore was fulfilled as a subcontract to Skanska Norway who is working on a US$17.3M expansion to the installation at Follafoss in partnership with Statkraft. US$7.8M of the project cost is attributed to tunnel work.

The 83m vertical shaft was drilled through granite using a TRB Rhino 2008H raisebore rig and then reamed using a Sandvik reamer head with 26 cutters.

Project manager for Skanska Raise Bore, Magnus Lingh, told T&TI it was a standard raise boring job apart for the diameter. He said the main distinction was that at 32t, the reamer head was too heavy to be lifted out at the top of the shaft and instead had to be lowered back down and removed at the bottom.

Skanska was awarded the shaft in September last year and had mobilised to site by late October. At a rate of 0.5m per hour, reaming was finished by mid-November.