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West Side CSO Tunnel Project, OR

The city of Portland needed to improve the quality of the Willamette River, a major tributary of the Columbia River. The West Side Tunnel aims to collect and store combined sewer overflows (CSOs) before they reach the river, and instead transports the overflow to a pump station, where it is treated before returning to the river.

120,000,000
Gallons Per Day Capacity
94%
Reduction in combined sewer overflows discharging untreated water to the Willamette River
2
Awards for Excellence and Safety

Overview

The project involved the construction of a new main sewer collection, storage, and conveyance system. The system included a deep storage and conveyance tunnel, a belowground pumping station, five shafts approximately 130 feet deep, and a network of micro-tunneled and open cut pipelines and diversion structures to connect existing sewers to the tunnel.

As part of a series of other CSOs projects, the combined projects reduced the city’s sewer overflows in the Willamette River by 94%.

Technical Highlights

Tunnel

  • Installation of an 18,180-foot tunnel, with an excavated diameter of 16.5 feet, and a pre-cast concrete bolted, gasketed segmental lining
  • Two 16.5-foot diameter, full face slurry mixshield tunnel boring machines (TBM) were used for excavation, marking the first use of this technology in the tunneling industry
  • No pre-excavation grouting from within the tunnel during mining with either TBM

Pumping Station

  • A 160-foot-deep and 137-foot-diameter pumping shaft
  • 120 million gallons per-day capacity
  • Excavation support consisted of a four-foot thick slurry wall extending to a depth of 200 feet
  • Internal wall consisted of cast-in-place concrete tied to the external slurry wall to form a final composite wall
  • Some of the deepest jet grouting columns in the world, at six feet in diameter each, extended 320 feet deep to tie into the top of a mudstone formation to form a groundwater cut-off wall

Pipelines

  • A micro-tunnel TBM with multiple shields and diameter varying from 84 inches to 108 inches was used for excavation and to install concrete PCP pipe lining
  • Overall pipeline length of approximately 15,000 feet

RECOGNITION

  • Accepted into the Voluntary Protection Program (VPP) from OR-OSHA for an exemplary safety record
  • 2006 Contractor of the Year from the Oregon Association of Minority Entrepreneurs