Evaluating Seismic Stability of Embankment Dams - Multiscale Geomechanics: From Soil to Engineering Projects - page 360

Figure 10.10. Pore pressure increase within a gravelly foundation
The failure evaluation is based on criteria taking into account the modeling
errors [FRY 03]. The validation of these criteria on real failures, such as the failure
of the San Fernando Dam, allows us to generalize their application to embankment
and rockfill dam projects. The criteria express the consequences of a seismic loading
at the end of the earthquake, considered as non-admissible in terms of strains,
irreversible displacements and liquefaction factor obtained by the numerical
modeling:
− The strains are analyzed by considering the evolution of the second invariant
of the strain tensor. The interpretation is based on the visualization of the kinematics
of failure or of highly sheared zones represented by the locus of the invariant's
biggest values. The threshold for the failure criterion corresponds to a shear strain
amplitude higher than 5%, following Seed's study [SEE 73]. A generalized failure
corresponds to a zone of shear strain amplitude above this threshold, crossing the
whole embankment from upstream to downstream.
− The threshold in displacement corresponds to a vertical settlement greater than
1/3 or 1/5 of the “freeboard” and to a horizontal displacement greater than 1/3 or 1/5
of the filter thickness or more than 1% of the dam height.
− The liquefaction factor is the ratio between the pore pressure increase and the
initial effective stress. Liquefaction is considered to be reached when this factor is
greater than 80%.