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Analyses are presented of the anticipated earthquake performance of three generally similar earth dams, situated in a seismically active area of northern California. The series of analyses illustrates a cost-effective approach which involved full-scale finite element analyses of one dam, and the use of limited dynamic analysis techniques and correlations to evaluate the other two. The simplified techniques were applied only after testing them against the finite element analyses, information is also presented on how the results of simplified and full-scale dynamic analysis procedures correlate.

Stevens Creek Darn is a rolled earthfill structure with a height of about 120 feet. A seismic safety evaluation in 1978 concluded that the darn would probably be severely damaged if subjected to a maximum credible earthquake originating on the nearby San Andreas fault. Normal reservoir operation was immediately restricted, pending decisions as to the fate of the project. Conceptual design studies were completed in 1982 to identify the most promising alternative remedial concepts. The most promising concepts were chosen and final design of modifications to the dam and its appurtenant hydraulic structures were completed in 1984. Modification of the darn was completed in 1986, involving the placement of massive buttresses on both the upstream and downstream slopes and installation of internal drains to control the phreatic line. This required extension of the existing outlet conduit and construction of new inlet and outlet control structures.