Analysis of the slides in the San Fernando Dams during the earthquake of Feb. 9, 1971

Report to the State of California Department of Water Resources, the Los Angeles Department of Water and Power, and the National Science Foundation.

Two major but old hydraulic fill dams were badly damaged during the 1971 San Fernando earthquake, but both dams retained their reservoir water. The Upper Dam suffered 6 ft of downstream sliding. With minor repairs it has continued to be in service. The Lower Dam suffered a major slide on the upstream zones seriously affecting the stability such that the reservoir water had to be drained and major repairs made. The results of a full scale major investigation are reported herein. Extensive field drilling, sampling, trenching and surveying were done. Laboratory static and cyclic loading tests were performed. Analytical studies were made using nonlinear response analyses based on the lab and field data. The results of these studies demonstrate why the particular modes of failure developed, and illustrate the ability of these analysis techniques to correctly predict the behavior of earth dams under earthquake loading conditions.