Portland's West Side Big Pipe North Drive is CompletedA Herrenknecht Mixshield TBM named Lewis (machine S-232) has broken through on 31st August into Confluent shaft on Swan Island after a 4-month subterranean crossing of the Willamette River in Portland, Oregon. The arrival at the base of the open-air shaft completed the north drive to Swan Island, one of the riskier parts of the West Side CSO tunnel or West Side Big Pipe project. The machine's 5.14 m-diameter cutter head displays the rock-cutting disks and other gear that helped it grind 1,350 m of tunnel through watery subterranean sand, gravel and boulders. The machine has dug while simultaneously laying segments of a precast concrete pipeline with an inside diameter of 4.27 m. Lewis is one of two Herrenknecht TBMs - the other is named Clark - on Portland's federally and state-mandated effort to stop most storm water and sewage overflows into the Willamette River. Clark (machine S-231) is a 5.05 m-diameter TBM which started excavating the 4,350 m south drive from Nicolai shaft in January 2004. At 14th August, 2004 progress had reached 930 m. The contractors are Impregilo and its US subsidiary S.A. Healy.Lewis began its main drive on 15th April, starting from Nicolai shaft near its assembly point at Nicolai Street in Northwest Portland's industrial district. The machine's arrival at Swan Island's Confluent shaft marks a milestone in the continuing tunnelling project. Tunnelling crews have crossed the river without any problems. The Confluent shaft is where the East Side and West Side Big Pipe tunnels eventually will meet. A smaller tunnel, one that a microtunnelling machine will bore, later will link the Confluent shaft with Swan Island Pump Station, the city's sewage treatment plant on North Columbia Boulevard. A month-long layover in the Confluent shaft will prepare Lewis for its final dig, tunnelling about 46 m to the base of another shaft that eventually will hold a pump station. The West Side CSO tunnel, nearly 5.65 km long, is set for completion in 2006. Construction of a planned East Side CSO tunnel, about 9.6 km long, runs from 2007 through 2011. Read E-News Weekly 25/2003, 38/2002 & 29/2002. Visit www.cleanriverworks.com or www.portlandonline.com/cso and www.herrenknecht.com 37/04. Photo courtesy of Sue Bednarz of Jacobs Associates for the City of PortlandClick on map to enlarge