Vinci Construction Grands Projets has been awarded a contract to construct two tunnels totalling 9.7km for the central section of the Brightwater wastewater collection system north of Seattle, US.
Vinci was awarded the work as leader (60%), in consortium with two American companies, Parsons RCI Inc (20%), a subsidiary of Parsons Corp, and Frontier-Kemper Constructors Inc (20%). Client, King County in Washington state, signed a US$211M contract with the consortium for the two tunnels that will be built as part of a 22km long system that will convey wastewater to a new treatment plant at Brightwater, from which it will be discharged into the sea after treatment.
The central section scope covers two tunnels of 6.1km and 3.6km long respectively. Vinci told T&TI that 5.3m diameter EPB machines rated at up to 7 bar would be used to bore through the ground.
The consortium will also excavate two access shafts, one 28m deep and the other 63m. A 1km long stretch of pipeline will be built to tie-in the new and old networks, of this, 500m will be built by microtunnelling. Works got underway in late August and are due to last for 51 months.
Also for the Brightwater scheme, Lovat announced that the JV of Kenny / Shea / Traylor has purchased a 5.8m diameter Lovat EPB machine for use on the 4.2km long tunnel to be built by the JV as part of its scope for the east contract section.
The mixed face TBM, due to be delivered in June next year, will be dressed with 32 no. ripper teeth that are interchangeable with 12” twin tip disc cutters. Operating at up to 3 bar, the TBM is expected to encounter sedimentary deposits comprised of fine to medium sands with organic silts, coarse sands and gravel with some clays and scattered boulders. The east tunnel alignment varies in depth from 12m to 82m and the water table is expected to range from 9m to 32m above the tunnel invert.
Contractors were invited to tender for the US$105.4M west tunnel of the Brightwater system by 21 September just before T&TI went to press. The scope includes 6.4km of 3.96m minimum diameter segmentally lined tunnel.
