Faraday Dam Improvements and Powerhouse Reconstruction, Estacada, Oregon
Portland General Electric (PGE) operates the Faraday Dam and Powerhouse on the Clackamas River near Estacada, Oregon. Faraday reservoir is retained by earth embankments, RCC walls, and a concrete gravity intake structure. To improve power generation, PGE recently replaced the original 1907 Faraday Powerhouse to enable installation of modern turbines. The improvements required replacing four existing penstocks, removing the existing powerhouse, and constructing a new, state-of-the-art structure designed for seismic resiliency and efficiency. Completing this work required substantial cuts and fills, with excavations up to 35 feet below average tail water, new foundations and structures, and a temporary cofferdam in the Clackamas River.

CCI-LT was retained by PGE as the geotechnical engineering consultant responsible for conducting subsurface investigations and site characterization, assessing the foundation conditions and stability of the concrete intake structure, developing geotechnical design recommendations for the new structures, performing design review of a temporary cofferdam, and providing engineering during construction and technical support.​
Picture
Targeted borings and downhole imagery were completed to characterize the concrete/rock interface for the Intake Structure.
Picture
Crews installing the turbines for Powerhouse 6 in 1956.
Project Highlights
​Subsurface investigations were conducted to fill data gaps that could not be gleaned from the original construction drawings. From the investigation results, our team developed foundation designs for the penstocks, floodwall, downslope thrust block, and the reverse bifurcation upper thrust block. HQ3 coring and downhole imagery were used at the intake structure to characterize the concrete/rock interface shear strength used in updated stability analyses. Statistical estimates of concrete strength were developed from laboratory test results following ACI Guidance. Recommendations for the new permanent structures also incorporated slake protection for the mudflow breccia that dominated foundation conditions at the site. Site-specific seismic studies were conducted to develop response spectra and design ground motions. Key design considerations for the project included stability of temporary excavations, blasting, temporary access, and surface runoff control.
​
CCI-LT provided on-site construction engineering and inspection once PGE broke ground, reviewing drawings, plans, and contractor submittals. Our personnel observed installation of soldier piles, micropiles, mid-slope anchors, rock bolts, and weep drains, and compiled installation data for submittal to the FERC. We worked closely with PGE and the contractor to determine solutions to construction issues that allowed work to resume safely with minimum amount of time lost.
Picture
Four of the existing penstocks were replaced at Faraday Dam as part of upgrades to modern turbines in the new powerhouse.
Picture
Historic Photo of the installation of the penstock for powerhouse 6 (circa 1955)
Owner: Portland General Electric
More Information: PGE - Modernizing our hydropower plants