Seismic Stability Analysis of Seepage Control Measures for Levees in Central Valley, California-Paper

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The paper presents a screening procedure for evaluating earthquake-related instability in infrequently loaded flood-control levees in California’s Central Valley. Although earthquakes are unlikely to coincide with flood conditions, liquefaction and ground deformation can damage levees and seepage-control features, including soil-bentonite cutoff walls, reducing protection before the next flood season.<br /><br />The procedure assesses liquefaction susceptibility and triggering, maps the longitudinal extent of potentially liquefiable soils, and estimates post-earthquake soil strengths. Engineers then conduct post-earthquake static and pseudo-static slope-stability analyses. Results are used to identify flow-failure risk, calculate yield acceleration where needed, estimate seismic deformation, and classify levees as having low, medium, or high vulnerability. Medium- and high-vulnerability levees may require repairs to both the embankment and its seepage-control measures.<br /><br />A Walthall Slough example illustrates the method. The analyzed levee section contained a roughly five-foot-thick likely liquefiable layer with low residual shear strength. Its post-earthquake factor of safety on the waterside slope was below 1.0, indicating potential flow failure and leading to a high-vulnerability classification. The predicted failure surface crossed the upper portion of the cutoff wall, creating a risk of seepage failure as well as major slope deformation.<br /><br />The paper concludes that this stepwise approach is suitable for screening levee seismic performance, while emphasizing the importance of estimating seismic soil properties accurately. Seismic damage assessments should account not only for levee-slope stability but also for the continued function of seepage-control systems.

Keywords

earthquake-related instability

flood-control levees

liquefaction susceptibility

ground deformation

seepage-control features

soil-bentonite cutoff walls

slope stability analysis

yield acceleration

seismic deformation

vulnerability classification