Analysis of Laterally-Loaded Piles in MSE Embankments

Bridge abutments supported on cast-in-drilled-hole (CIDH) piles embedded in mechanically stabilized earth (MSE) retaining walls are becoming increasingly common in California. Pile behavior under lateral (e.g., earthquake) loading for this relatively new abutment system is currently not well established. To that end, three-dimensional finite element modeling is undertaken for a representative pile-supported MSE abutment with wrap-around MSE walls retaining the approach embankment on the two longitudinal sides and beneath the bridge deck. In this configuration, seven 0.9-m (3-foot) diameter CIDH piles in a single row extend 7.6 m (25 feet) above native subgrade inside the MSE wall, and connect to the abutment footing. The piles are located close to the wall face, at a longitudinal clearance of 0.46 m (18 inches). Lateral pile top loading is applied to the finite element models in the longitudinal and transverse directions separately, in two sets of analyses. Under longitudinal pile top loading, the response of the single row of piles is found to be dictated primarily by the properties of the MSE reinforcement material. In contrast, the response under transverse loading is found to be governed significantly by the soil resistance in between the seven piles. For use in repetitive design iterations, simplified beam-spring analysis procedures are developed, similar to those used for ordinary level-ground lateral pile analysis. Design recommendations based on the simplified models are found to compare well with results from the finite element analyses.