Liquefaction Analysis of the 1971 Ground Failure at the San Fernando Valley Juvenile Hall, California

A lateral spread seriously damaged the San Fernando Valley Juvenile Hall during the 1971 San Fernando earthquake. A subsurface investigation in 1981 was conducted using cone penetration and standard penetration tests to define the stratigraphy and to obtain samples and penetration data for a liquefaction analysis. The investigation showed that a loose layer of sandy silt and silty sand at a depth of approximately 4.5–5.5 m (14.8–18.0 ft) liquefied during the earthquake. The liquefaction zone is located in a layer of sediment estimated to be younger than 10,000 yrs. Sediment underlying the failure zone, which is estimated to be older than 35,000 yrs, is marginally to highly resistant to liquefaction-induced ground failure.