Use of Centrifuge and Numerical Modeling in Design of Pier 400 at the Port of Los Angeles

Port of Los Angeles (POLA) is involved in the creation of 235 ha (580 acres) of new land called Pier 400 by dredging and landfilling behind rock dikes. Because of the complicated nature of the project, POLA chose a fully coupled, elastoplastic, dynamic finite-element code called DYSAC2 as part of the seismic design of Pier 400. The predictions made by DYSAC2 were first validated using dynamic centrifuge model tests. Centrifuge model tests consisting of gravel dikes retaining sand backfills overlying stratified foundation soils also provided insight into the expected deformation mechanisms of Pier 400 cross sections. Centrifuge models indicated that the dikes will move more or less as a rigid block with most of the lateral deformations being concentrated in the foundation soils. These observations were confirmed by analyses of centrifuge models and Pier 400 cross sections using DYSAC2. Because of the rigid body movement of the dikes, a hybrid analysis procedure, between simplified Newmark’s method and the DYSAC2 analysis procedure in sophistication, was developed for the lateral deformation calculations of the Pier 400 cross sections. The hybrid method is similar to Newmark’s method, but yield acceleration values are calculated using average excess pore pressures predicted by DYSAC2 in the foundation soils and the landfill. In essence, the Pier 400 design team and POLA used results from sophisticated fully coupled procedures and centrifuge model tests together with traditional embankment analysis techniques and engineering judgment to produce a viable and safe seismic design of Pier 400 dikes and landfill.