Effects of soil density and earthquake intensity on flow deformation of the upper San Fernando dam

The seismic performance of the upper San Fernando dam is systematically studied by using a fully coupled finite-element procedure in conjunction with a unified state-dependent dilatancy sand model. With detailed information produced by this procedure, the effects of soil density and earthquake intensity on flow deformation of the embankment are examined. This paper provides convincing numerical evidence to prove that even though stronger earthquakes always produce larger deformation in the Upper San Fernando dam, an earthquake serves mainly as a trigger to initiate flow liquefaction. Once flow liquefaction is triggered by a sufficiently strong earthquake, the earthquake-induced flow deformation is controlled dominantly by the difference between the shear stress required for equilibrium and the shear strength of the liquefied soil, which is determined by its density under undrained earthquake loading conditions. The influence of the intensity of the earthquake itself on flow deformation of the embankment becomes secondary.