Professor Raymond B. Seed, PhD, Professor Emeritus, U.C. Berkeley & Dr. Khaled Chowdhury, U.S. Army Corps of Engineers
Talk Title: Lessons Learned from Back-Analyses of the Upper and Lower San Fernando Dams Using Nonlinear Seismic Deformation Analyses
Abstract: The seismic performances of the Upper San Fernando Dam and the Lower San Fernando dam during the 1971 San Fernando earthquake were foundational to the inception of the U.S. national seismic dam safety programs still ongoing today. The Lower San Fernando Dam experienced a liquefaction-induced upstream flow failure, reducing remaining freeboard to a perilously low margin until the reservoir was safely drawn down, and the Upper San Fernando Dam experienced more limited deformations including approximately 3 feet of crest loss and 7 to 9 feet of lateral translation of the downstream face due to cyclic pore pressure generation and strong seismic inertial lurching forces. Together, these two case histories are an excellent test for liquefaction-related analytical methods because they represent two different, and important, types and ranges of performance: (1) potentially catastrophic flow failure, and (2) small to moderate deformations and displacements, for two co-located dams with outwardly similar design and construction histories and methods of construction. This presentation will present the results of recent studies in which fully nonlinear seismic deformation back-analyses were performed for both dams using combinations of (1) four different analytical or constitutive models, (2) three different liquefaction triggering relationships, and (3) three different post-liquefaction residual strength (Sr) relationships. These studies found that these types of analytical methods and relationships can be powerful and useful engineering tools, providing very good “predictions” of the observed field performance behaviors. Not all analyses were successful, however, and these studies also show that producing useful and accurate engineering results appears to require suitably addressing a number of key issues and details; and these are enumerated. Lessons learned extend well beyond dams, and apply to liquefaction-related engineering analyses and evaluations of many additional types and classes of projects.
Professor Raymond B. Seed earned his BS, MS, and PhD from the University of California at Berkeley. He taught at Standford University for four years, and then moved to UC Berkeley where he had a teaching and research career for 30 years. Professor Seed’s research has had a significant impact on geotechnical practice in a number of areas including: analysis of compaction-induced stresses and deformations, seismic stability analysis of dams and embankments, analysis of soil liquefaction potential and post-liquefaction behaviors, analysis of reinforced soil systems and deep braced excavations, effects of site conditions on seismic site response, finite element analysis of static and seismic soil-structure interaction, stability and performance evaluation for hazardous waste fills, geotechnical evaluations and mitigation of dams and levees, and others.
Dr. Khaled Chowdhury has over 18 years of experience in evaluations, design, and construction of infrastructure projects. Dr. Chowdhury worked for AECOM (formerly URS) and Kleinfelder for 16 years prior to joining USACE’s South Pacific Division Dam Safety Production Center in Sacramento. He was a co-author or reviewer for several dams and levee Guidance Documents or Engineering Manuals for the CA DWR and USACE. He has several technical papers on topics such as seismic evaluations of dams and levees, seepage, stability, seepage cutoff walls, site characterizations. His PhD at the University of California at Berkeley focused on the evaluation of the State of Practice regarding analysis of seismic performance of potentially liquefiable dams based on case histories. Dr. Chowdhury is a Professional Engineer and Geotechnical Engineer in California.