$1Kleinfelder, 3077 Fite Circle, Sacramento, California 95827, USA; There are 1,600 miles of Federal project levees maintained by the State of California with additional 1,100 miles of non-project levees. Many of these levees are Legacy levees having been originally built in early the 1900's. These levees protect the water supply to 23 million people, protect a population of about 400,000 from floods and provide crucial support to the state economy. Being located in an area of high seismic activity, levees and floodwalls protecting urban and rural but urbanizing areas in California require seismic analyses to assess the potential instability due to liquefaction, lateral spreading and associated vertical and lateral deformations. However, the risk of seismic hazard needs to be balanced against the need to address more immediate and potentially higher risk static hazards. These analyses help the State of California and local agencies to make decisions regarding mitigation strategies for Legacy levees subject to potential overtopping, seepage and stability failures. Recently, the California Department of Water Resources (DWR) published interim guidelines outlining seismic screening methodologies for levees and floodwalls (DWR, 2010). Depending on the nature of the levees and results of analyses, implications of seismic issues could be quite significant on the stability of the levees, protection of the surrounding urban areas and subsequent mitigation and contingency strategies. This paper provides a detailed step by step procedure developed by Kleinfelder for conducting a screening level analysis including estimating ground motions, performing liquefaction analyses, and assessing seismic stability of levees under design level earthquakes. Design level earthquakes are based upon an equal hazard probability similar to the design flood. Impacts of static shear stresses within and beneath the levees and the presence of non-plastic clays and silts on the liquefaction analysis will be presented. Example problems will be presented to further explain the seismic analysis methodology.
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