Installation of Rock Bolts above the Flume
The J.C. Boyle Dam is part of the Klamath River Hydroelectric Project. The dam diverts water from the Klamath River into a concrete flume that runs parallel to the river for several miles. On the morning of December 2, 2005 a major rockfall impacted the flume and punched an approximate 6 ft. by 8 ft. hole in its wall. The resulting flow through this breach caused considerable erosion to the slope below the flume and created a large scour channel. The source of the rockfall was an approximately 55-foot tall rock cliff located over 200 vertical feet above the flume.
PacifiCorp Energy retained Landslide Technology (LT) on an emergency basis to evaluate the failure and immediately provide remedial measures. A rockfall construction contractor was retained within a few days to proceed with the corrective work. Corrective measures consisted of an embankment using compacted rockfill to re-establish the slope below the flume, removal of rockfall debris, daily rock slope observations and rockfall spotting activities, flume wall repair, and guardrail replacement. No rock slope remediation was done. Work was completed in record time which allowed PacifiCorp Energy to resume hydroelectric production.
On December 22, 2005 another rockfall event occurred that destroyed an approximately 10-foot section of the newly replaced guardrail, resulting in a temporary closure of the upper road. The rockfall consisted of an approximately 6-foot diameter rock block that came from near the top of the vertical rock outcrop. As a result of this separate incident, PacifiCorp authorized LT to develop and design rockfall mitigation measures. The rockfall mitigation measures included hand scaling, cable lashing, draped cable nets, bolting and doweling of key rock blocks, and installation of a rockfall attenuator fence.