This paper describes a centrifuge study undertaken to investigate how sand gradation affects the system-level performance of embankments subjected to strong shaking. Current analysis and design practices are primarily based on knowledge from case history records of liquefaction, with the majority of those from sites consisting of clean, poorly graded sands. The narrow range of gradation characteristics represented in the case history database poses a challenge during the analysis of embankment structures traditionally constructed with, or founded on, more broadly graded soils. The tests herein were designed to elucidate how embankments uniformly constructed with a well graded and poorly graded sand perform differently during earthquake shaking. A centrifuge experiment test program was developed and conducted using the 9-m-radius centrifuge at the UC Davis Center for Geotechnical Modeling. The experiment design consisted of two submerged 10-degree embankments positioned side-by-side in the same rigid model container, with one embankment constructed with poorly graded sand and the other with well graded sand. The embankments were dry pluviated to the same relative density, but the absolute densities of the sands were different. The embankments were identically instrumented with dense arrays of in-situ sensors beneath the level ground above the slope and in the mid-slope to measure the dynamic response during liquefaction. Results showed that embankments constructed at equal relative densities would both liquefy (i.e., ru reach 1.0), but deformations were less severe for the embankments constructed with the well graded sand. Greater resistance to the generation and faster dissipation of excess porewater pressures, coupled with stronger dilatancy of the well graded sand increased embankment stability, curtailing liquefaction-induced deformations.

PREdiction of NOn-LINear soil behavior (PRENOLIN) is an international benchmark aiming to test multiple numerical simulation codes that are capable of predicting nonlinear seismic site response with various constitutive models. One of the objectives of this project is the assessment of the uncertainties associated with nonlinear simulation of 1D site effects. A first verification phase (i.e., comparison between numerical codes on simple idealistic cases) will be followed by a validation phase, comparing the predictions of such numerical estimations with actual strongmotion recordings obtained at well-known sites. The benchmark presently involves 21 teams and 23 different computational codes. We present here the main results of the verification phase dealing with simple cases. Three different idealized soil profiles were tested over a wide range of shear strains with different input motions and different boundary conditions at the sediment/bedrock interface. A first iteration focusing on the elastic and viscoelastic cases was proved to be useful to ensure a common understanding and to identify numerical issues before pursuing the nonlinear modeling. Besides minor mistakes in the implementation of input parameters and output units, the initial discrepancies between the numerical results can be attributed to (1) different understanding of the expression “input motion” in different communities, and (2) different implementations of material damping and possible numerical energy dissipation. The second round of computations thus allowed a convergence of all teams to the Haskell–Thomson analytical solution in elastic and viscoelastic cases. For nonlinear computations, we investigate the epistemic uncertainties related only to wave propagation modeling using different nonlinear constitutive models. Such epistemic uncertainties are shown to increase with the strain level and to reach values around 0.2 (log10 scale) for a peak ground acceleration of 5 m=s2 at the base of the soil column, which may be reduced by almost 50% when the various constitutive models used the same shear strength and damping implementation.