SAGE was hired to design rockfall protection structures for New Exchequer Dam. The rock slopes that form the downstream abutments of the dam are approximately 450 feet tall and are comprised of very steep to vertical rock outcrop bands and prominent rock pinnacles, with areas of less steep talus and colluvium slopes between them.
The protection structures would consist of rock anchors, tie-backs, drapery systems, and flexible rockfall catchment barriers to reduce rockfall risk to personnel and equipment at the hydroelectric power plant and access road at the base of the dam.
Given the complexity and variety of terrain exposed on the abutments, SAGE coordinated with a 3-D imaging sub-consultant to perform a ground-based LIDAR (Light Detection and Ranging) survey of the site. The detailed topography generated by the LIDAR survey was used as a base map for the geologic reconnaissance, rockfall modeling of the slope, and the layout and analysis of slope support.
SAGE geologists performed a field reconnaissance with mapping efforts focused on areas with oversteepened or overhanging rock faces, joint/fracture dilation, recent block failures, and other areas where the aspect, inclination, and structural features that formed potentially unstable conditions prone to future failures. Orientations of structural discontinuities collected during our field reconnaissance were analyzed using stereonet and slope stability analysis software to evaluate the potential failure modes that might occur.
Detailed rockfall simulations were run to estimate rockfall energies and bounce heights for a design of rockfall catchment barriers and a roof structure for the penstock access pit at the base of the dam.
The results of our evaluations were used in preparing Plans, Specifications, and Estimate (PS&E) documents and accompanying Design Basis Letter. Plan submittals included 50%, 90%, and 100% design drawings reviewed by MID and FERC.