Salvation in Seattle BT3C Completes Boring on Brightwater

THE 13-MILE (21km) long Brightwater tunnel is the main component of a $1.8 billion project to increase sewage treatment capacity in the greater Seattle region of King County, Washington. The 13-17ft (4-5m) i.d. tunnel – which was split into four excavation contracts (Figure 1) – has been bored at depths of up to 475ft (144m) using two Lovat EPBMs and two Herrenknecht Mixshields and has involved some of the longest and most challenging soft ground drives in the US to date.

The tunnel will ultimately collect flows from two existing trunk sewers and divert them to the new Brightwater treatment facility. Once treated, effluent will also be conveyed back through the tunnel to a new 1-mile (1.6km) long marine outfall in the Puget Sound. Read more...