Three-dimensional dynamic response analyses of Cogswell Dam

Abstract

The recorded strong motions at Cogswell Dam during the 1987 Whittier Narrows and 1991 Sierra Madre earthquakes provide a valuable opportunity to evaluate the applicability of established engineering procedures for evaluating the dynamic response of dams with highly three-dimensional geometries. In addition, these records provide an opportunity to back-calculate the dynamic properties of rockfill materials, which cannot be easily measured in the laboratory or in situ. Peak transverse crest accelerations of 0.15 g and 0.42 g were recorded during the Whittier Narrows and Sierra Madre earthquakes, respectively. Combined with analyses of the trailing portions of these strong motion records, the field data cover a wide range of induced shear strains. Two-dimensional and three-dimensional dynamic response analyses were performed using established engineering procedures, and their results are compared with the recorded responses. Dam–canyon interaction and topographic effects appear to have influenced the seismic response of the dam significantly. Estimates of the in situ dynamic rockfill properties, including the modulus degradation relationship, are presented. Key words : rockfill, dynamic properties, embankment dams, earthquake response.