UC Davis

The Canterbury Earthquake Sequence produced a spatial pattern of liquefaction-induced surface ejecta at an open field along Palinurus Road in Christchurch, New Zealand, that would not be expected based on simplified liquefaction evaluation procedures. Half the site discharged sand boils and the other half did not. Two-dimensional fully-coupled nonlinear dynamic analyses (NDAs) were performed to examine why simplified one-dimensional liquefaction vulnerability indices (LVIs) overestimated liquefaction manifestations at this site for the 2010 Darfield and 2011 Christchurch earthquakes and did not distinguish between areas with and without surface ejecta. The NDAs use the PM4Sand and PM4Silt constitutive models for sand-like and clay-like portions of the subsurface, respectively, within the Fast Lagrangian Analysis of Continua (FLAC) finite-difference program. Material parameters are obtained from in situ geophysical and cone penetration test (CPT) data. A sensitivity study is performed to assess the influence of (1) representative soil property selections and the use of a CPT inverse filtering procedure to correct for thin-layer and transition zone effects, (2) ground motions developed by two distinct methods (i.e., recordings and physics-based simulations), and (3) model assumptions affecting diffusion during reconsolidation. Ground deformations and flow patterns during and after ground shaking are examined. The results provide insights on how stratigraphic details and other factors can affect the system response and dictate the degree and extent of liquefaction surface manifestations.