Upper San Fernando Dam Construction Methods and Implications on the Modeling of Its Seismic Performance

The 1971 San Fernando and 1994 Northridge earthquakes significantly shook the Upper San Fernando Dam (USFD) and substantially deformed its hydraulic fill embankment. Extensively analyzed, this dam has become a landmark case study for validating numerical models, despite its poorly documented construction methods. Following the 1971 earthquake, most analysts assumed a semi-hydraulic fill method of construction as well as a firm foundation. They also thought that the outlet line, damaged in 1971, was within the hydraulic fill materials and deformed with them. These assumptions have influenced the interpretation of the USFD performance and every numerical simulation of its seismic behavior. Based on a thorough review of archives, we confirm that the dam was constructed using the full hydraulic fill method and that the outlet line was within alluvium soils and suffered damage in 1971 when those deformed. We propose cross-sections to refine numerical models and describe what aspects are needed to validate the dam's seismic performance accurately.