Dynamic Deformation Analysis and Three-Dimensional Post-Earthquake Stability Analysis for Casitas Dam, California: Fid-Bau Portal

Dynamic Deformation Analysis and Three-Dimensional Post-Earthquake Stability Analysis for Casitas Dam, California

France, John W. / Adams, Tiffany / Wilson, John / Gillette, Dave

Casitas Dam is a 335-foot high, zoned earthfill embankment located in a highly seismic area, near Ventura, California. The U.S. Bureau of Reclamation (Reclamation) concluded that the foundations of the dam were susceptible to liquefaction in the event of an earthquake, and that liquefaction of the foundations could lead to failure of the embankment and uncontrolled release of the reservoir. Reclamation developed designs for dam safety modifications to increase the seismic stability of the downstream section of the dam, but the planned modifications do not include treatment of the upstream foundations. Two-dimensional dynamic deformation analyses and three-dimensional post-earthquake stability analyses were performed to evaluate the expected performance of the untreated upstream slope during and after significant earthquake shaking. The deformation analyses indicated that significant deformations would be expected in the upstream section of the embankment dam, but that freeboard would be maintained at the downstream edge of the crest of the modified dam. The three dimensional stability analyses indicated that three-dimensional factors of safety for the upstream slope that were between 10% and 35% higher than the corresponding two dimensional factors of safety. Based on these results, the two-dimensional stability analyses may be over-estimating the deformations in the upstream section of the dam. This paper includes a discussion of the methods used in the analyses, the results obtained, and limitations and other issues that had to be addressed to complete the analyses.