Analysis of Earth Dam Response to Earthquakes

An investigation has been made of the effect of two earthquakes with Richter local magnitudes ML of 6.3 and 4.7 on a modern rolled-fill earth dam in Southern California. The dam was equipped with motion sensors that yielded data on the structural response as well as the ground input motion at the site. Amplification spectra of the dam were computed for the two earthquakes to indicate the natural frequencies of the dam, to estimate the shear-wave velocity of its materials, and to estimate the relative contribution of different modes of vibrations. A comparison between the aforementioned natural frequencies and those obtained for the dam by existing shear-beam theories was made to obtain representative dam material properties. In addition, field wave-velocity measurements were carried out as a further check as well as to study the variation of shear-wave velocity (or shear modulus) at various depths below the crest of the dam