West side cso tunnel project, shafts, pumping stations and channels (Portland, Oregon - Usa) - contract no. 34448

Name of Project:

West side cso tunnel project, shafts, pumping stations and channels (Portland, Oregon - Usa) - contract no. 34448


City of Portland - BES - Bureau of Environmental Services

Construction period:
September 2002 - September 2006

The project was set up to improve the sewage system of the city of Portland (Oregon), by eliminating the Combined Sewer Overflows (CSO) that discharge into the Willamette River. It involved construction of a new main sewer collection and storage system for the west city area, including a 5.5 km tunnel, a pumping station, five service shafts approximately 40m deep, and a network of micro-tunnels to connect existing sewers to the tunnel. The work was conducted in saturated soils, variable from sand up to cobbles and boulders, below the water table. It took place in an urban area.

Main project features
CSO Tunnel – length 5,533 m , internal diameter 4.26 m, with pre-cast concrete bolted, gasketed segmental lining. Excavation work was carried out by two full-face slurry-shield Herrenknecht TBMs, 5.02 m in diameter.

Shafts - The Nicolai shaft is the main work shaft and is 36.48 m deep with a 16.11 m internal diameter. Four other shafts have internal diameters ranging between 11.9 m and 14.6 m and depths between 34 m and 43m.

Pumping Station - The pumping station shaft is 38.30 m in internal diameter and 45.60m deep.

Pipelines - The project included a micro-tunnel network to connect the existing sewage network to the newly constructed shafts. A Herrenknecht micro-tunnel TBM with diameter varying from 2.25 m to 2.75 m was used to excavate the secondary tunnels and lay the concrete pipelines. The overall length of the pipelines was more than 3,420 m.

Underground excavation (main tunnel and micro-tunnels): 132,200 m3
Pre-cast segments for tunnel lining: 20,700 m3
Shaft excavation: 95,000 m3
Jet grouting: 17,600 m3
Slurry walls: 18,600 m2
Pump station concrete: 25,000 m3



Last update: 18/09/2013