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Excavated soil is shipped by barge to Ross Island for use in wetlands restoration. |
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PB explored Portland's underlying geologic formations. (Photo by S. Bednarz) |
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Building a Big Pipe
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Since June 2000, PB has provided the City of Portland's Bureau of Environmental Services with final design and design services during construction for the West Side CSO tunnel, shafts, pump station and pipelines. In addition to total project oversight, the firm has provided phased onshore urban and offshore geotechnical investigations for all elements of the project.
In-depth research on the history of infrastructure development along the Willamette waterfront enabled PB to develop a plan and profile that avoided the buried, manmade structures along the river's shoreline. The team evaluated sediment loading, deposition, re-suspension and transport to ensure the tunnel design would properly manage sediment. Other tunnel design attributes that were evaluated and determined using the hydraulic model included diameter, gradient, transients, hydraulic relief, air relief/foul air control and drop-shaft compatibility.
The West Side CSO project features the first use of a large-diameter slurry mix-shield tunnel boring machine (TBM) in the United States—two of them, in fact, named Lewis (northbound) and Clark (southbound). As work continued, excavated soil from the face of the TBM was pumped back through the tunnel to the primary access shaft and then shipped by barge to Ross Island for use in wetlands restoration.
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