RCC For Seismic Design

by Noel C. Wong, Group Director; Geoengineering, Woodward-Clyde Consultants, Oakland, Calif.,
Michael P. Forrest, Sr., Project Engineer; Woodward-Clyde Consultants, Oakland, CA,
Sze-Hang Lo, Project Manager; Woodward-Clyde Consultants, Oakland, CA,


Serial Information: Civil Engineering—ASCE, 1994, Vol. 64, Issue 9, Pg. 60-62


Document Type: Feature article

Abstract:

Throughout its 70-year existence, the Littlerock Dam in Southern California's National Forest has been the subject of concern. Located only 1.5 mi south of the San Andreas fault, could this historic 28-arch dam withstand any major movement from that fault line, much less the big one? The state's Division of Safety of Dams asked Woodward-Clyde Consultants, Oakland, Calif. to perform stability and stress analyses to find the answer. Our research showed that, as feared, the dam failed to meet required seismic safety criteria, principally due to its lack of lateral stability, a deficiency inherent in multiple-arch dams. To provide seismic stability, the engineers developed a rehabilitation design centered around the use of roller compacted concrete (RCC) to construct a gravity section between and around the downstream portions of the existing buttresses. We also proposed that the arches be resurfaced and stiffened with steel fiber-reinforced shotcrete with silica fume. The alternative design would have required filling the arch bays between the buttresses with mass concrete at a cost of $22.5 million. The RCC buttress repair construction will cost about $12.5 million.

Subject Headings: Seismic design | Dam failures | Seismic tests | Arches | Stress analysis | Roller-compacted concrete | Mass concrete

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