Corps drills into Cougar Dam for geotechnical investigation

The U.S. Army Corps of Engineers’ Dam Safety team is conducting a geotechnical investigation at Cougar Dam beginning today, Friday, Sept. 20.

Geotechnical investigations sample the constructed material of the dam. The investigation involves boring into the dam material to test soil grain size and related strength properties. The goals of this drilling investigation are to better understand the dam’s material properties and to provide long-term monitoring of the dam.

The work includes drilling 11 holes along the dam crest. Crews will add two new piezometers to monitor the internal pressures over time and at various reservoir levels. This work is part of a larger risk assessment in which data from the borings will inform future analysis of how the dam will perform under various conditions, such as flooding or earthquakes. 

“This assessment involves drilling completed by a roto-sonic drill rig and a crew out of Savannah, Georgia,” said Adam Jones, Portland District geologist. “This is a specialized machine that is able to drill through rock and gravel safely and efficiently.”

The Corps' dam safety program works to minimize risks to the public for the dams it owns and operates. The issue evaluation study and the drilling investigation are part of the Corps’ dam safety program which includes training, routine inspections, monitoring, Emergency Action Plan exercises, and risk assessments.

The drilling will occur through Oct.1. During this time, one lane will be closed on National Forest Road 1993. This road runs along the face of the dam to the east side of the reservoir.

Cougar Dam is located on the South Fork McKenzie River of the Willamette River east of Eugene, Ore.