A number of earth and rockfill dams, instrumented with strong ground motion recorders, experienced the Whittier Narrows earthquake of October 1, 1987. The closest was the Whittier Narrows Dam, at 4 kilometers distance from the earthquake's epicenter. The maximum horizontal acceleration was 0.32g recorded at the crest of the dam, while the upstream recorder indicated a peak vertical acceleration of 0.46g. The response of other dams at greater distances was also obtained. Few strong motion records are available for such structures. This project addresses the analysis of these records from nine earth dams in order to understand the behavior of earth dams, and the utility of different analytical models for the analysis of dam response. The shaking during the main shock, as well as the after shocks, triggered all accelerographs on the nine dams, providing the most extensive array of earthquake response measurements of earth dams yet obtained in the U.S. and abroad. It is a cooperative project between the California Institute of Technology and the University of Southern California. Three major tasks are being addressed: (1) data processing, analysis, and comparison of accelerograms; (2) evaluation of internal permanent deformation and cracking in the dams; and (3) summarizing the observations, results, and conclusions in a general recommendation for the strengthening of earth dams for earthquake resistance. The California Institute of Technology is concentrating on performing centrifuge tests on physical models of one or two of these dams, while the University of Southern California is concentrating on both simplified and complex numerical models of nine dams. A comparison is being made of the results of the centrifuge tests, the observed response of the dams during the Whittier Narrows earthquakes, and the results of the computer analysis using the numerical models.
