Willamette

Willamette Falls Dam is a turn-of-the century concrete dam along the lip of Willamette Falls in Oregon City, Oregon. Cornforth Consultants performed geotechnical services in connection with Federal Energy Regulatory Commission (FERC) dam safety inspections for the owner and operator Portland General Electric.

In an early study, Cornforth Consultants drilled through the dam to collect core samples of the concrete-bedrock interface and install piezometers to obtain information on the interface shear strength and uplift forces. Five borings were drilled using a barge on the forebay side of the dam, and one was drilled through the wall of a paper mill.

In a subsequent study, Cornforth Consultants performed stability analyses for critical dam sections according to FERC guidelines for usual, flood and extreme (seismic) loading conditions. Ground motion studies were also performed to develop peak ground acceleration for the pseudo-dynamic analysis. In a more recent study, sliding analyses of a structurally complex section of the dam was performed using an innovative analysis technique developed by a Cornforth Consultants engineer, which was reviewed and approved by FERC.