PROJECT: WILLAMETTE FALLS DAM STABILITY ANALYSIS, Oregon City, Oregon


Willamette Falls Dam Subsurface Investigations

Willamette Falls Dam is a 100-year-old concrete dam located near Willamette Falls in Oregon City. Cornforth Consultants (CCI) 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 phase, CCI 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 from a barge on the forebay side of the dam, and one was drilled through the wall of an adjacent paper mill.

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