ESTIMATION OF EARTHQUAKE-INDUCED PERMANENT DISPLACEMENTS IN EMBANKMENT DAMS

The research study presented herein gives a detailed evaluation of earthquake-induced permanent displacements in embankment dams using Makdisi-Seed simplified procedure as well as by full-scale dynamic response analyses employing finite element technique.; Four homogeneous and seven zoned earthfill dams under the jurisdiction of the State of California, Department of Water Resources, were selected for the study. The main factors considered in the selection were embankment type and configuration; foundation type; and availability of pertinent data including shear strength and dynamic properties of the materials, post-construction field and laboratory test results, vicinity from major active faults, and seismicity of the area. The dams consist predominantly of well-compacted clayey soils and dense granular materials placed on sound alluvium clay or bedrock foundation. These design and construction features strongly favored use of the deformation criterion for seismic evaluation.; Both the Makdisi-Seed simplified procedure and the step-by-step finite element method used in this study require the determination of the yield acceleration k{dollar}sb{lcub}rm y{rcub}{dollar} of the critical potential sliding mass of specified depth and yield strength, and the maximum average acceleration k{dollar}sb{lcub}rm max{rcub}{dollar} of the sliding soil mass due to a certain earthquake. In both cases, values of k{dollar}sb{lcub}rm y{rcub}{dollar} were determined using computer program BISHOP. In the simplified procedure, both k{dollar}sb{lcub}rm max{rcub}{dollar} and permanent displacements were estimated using the design charts developed by its authors (Makdisi and Seed, 1977). Values of k{dollar}sb{lcub}rm max{rcub}{dollar} used in displacement evaluations employing finite element technique were calculated from average acceleration time-histories established using the 2-D finite element computer program QUAD-4.; The study concludes that the Makdisi-Seed simplified procedure for estimating earthquake-induced permanent displacements may be employed, with reasonable accuracy, to both homogeneous and zoned embankment dams, particularly, during planning and design phases when earthquake resistance of various cross-sections and material types for the proposed facility need be evaluated. It should, however, be emphasized that whichever method is adopted for preliminary and/or final seismic evaluations, the nature of approximations involved will necessitate great caution and good engineering judgment in the interpretation and application of the results. (Abstract shortened with permission of author.)...