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The Portland "Big Pipe" Tunnel and Pipeline Projects: Using Geology and History to Reduce Construction Risk
Thursday, December 4, 2008 - 7:30pm

Sigma Xi Columbia-Willamette Chapter presents

The Portland "Big Pipe" Tunnel and Pipeline Projects: Using Geology and History to Reduce Construction Risk


Sue Bednarz
Engineering Geologist, Jacobs Associates

Thursday, December 4, 7:30 pm
Smith Memorial Union 296-298

Portland State University
Free admission
The public is invited

The Big Pipe projects are the largest and most important components of the Willamette River CSO Program in Portland. The two Big Pipe tunnels, which parallel the east and west shoreline of the Willamette River, collect and transport combined storm water and sanitary sewer overflow (CSO) to prevent discharge into the river during storm events. The 14-foot diameter West Side Big Pipe was completed in 2006 and the 22-foot diameter East Side Big Pipe is currently under construction. In addition to the two larger tunnels, connecting CSO pipelines have also been constructed or are currently under construction. These pipelines collect and transmit CSO flows.

To support the design and construction of the tunnels and connecting pipelines through an urban area, geologic modeling of subsurface conditions was performed using borehole data and historical research. In the end, buried obstructions that were identified through historical research and bridge and building foundation evaluations were critical in determining both the location and depth of the tunnels and pipelines. These obstructions, if encountered during tunneling, would result in project delay and increased cost.

This talk describes the techniques that were used to model geologic conditions and identify buried obstructions for the West Side Big Pipe project. The talk also includes a discussion of how buried obstructions shaped both Big Pipe tunnel alignments and the alignments of the connecting pipelines. Construction photographs showcasing the construction of both the tunnel and pipeline projects are included in the presentation.

Sue Bednarz, a native Oregonian, is a Certified Engineering Geologist with Jacobs Associates who has been responsible for geologic modeling and subsurface investigations for the Big Pipe projects in Portland, Oregon. Sue has a B.S. degree in Geology from Oregon State University and an M.S. degree in Engineering Geology from Portland State University. She has over 12 years experience with geologic and geotechnical characterization of tunnels, shafts, pipelines, bridges, buildings, highways, and landslides.