| Many bridge foundations have suffered damage in liquefied and laterally spreading ground in past earthquakes. The damage could range from negligible, to moderate repairable, to extensive. The soil profile in liquefiable ground often consists of a nonliquefiable crust layer overlying the liquefiable layer. Recent research showed that the load transfer behavior between the laterally spreading nonliquefied crust and bridge foundations may be an order of magnitude softer than that from static load tests. Finite element simulations were utilized to explore the effect of the strength of the underlying weak material and the depth to the underlying weak layer on the softening load transfer relations. The softening effect was most pronounced when the underlying soft layer was weakest and the depth to the underlying weak layer was smallest.;Case histories with poor and good performance of pile-supported bridge foundations were analyzed using probabilistic beam on nonlinear Winkler foundation simulations that quantify the uncertainty in ground motion prediction, liquefaction triggering evaluation, lateral spreading displacements, and structural response. Different previously published approaches predict very different lateral spreading displacements that have significant influence on foundation response, especially for weak flexible foundations.;Site conditions exert significant effects on earthquake ground motions and therefore structural response, especially for liquefiable soils. Numerical site response analyses were performed and demonstrate that large-amplitude accelerations can propagate through liquefiable soils towards the ground surface due to the dilatancy behavior of liquefied sand, thus, the inertia demand should be considered simultaneously with the kinematic demand in foundation design. Monte Carlo simulations of site response were utilized to generate the site amplification factors to estimate the effect of liquefaction on ground surface motions, and therefore on inertia loads acted on structures. Generally, liquefaction attenuated ground surface motions.;The continuous superstructure can transfer lateral loads among bridge components and restrain the longitudinal deformation of bridge foundations. Local static pushover analyses with the boundary conditions generated from global dynamic analyses were performed to propose a method for estimating pier top displacement constraint. Using the estimated boundary condition, static simulations can reasonably well predict structural deformation under lateral demands. Guidelines for deep foundation design subjected to lateral spreading and inertia loading were proposed. |
