Design of Pile Foundations for Liquefaction-Induced Lateral Spread Displacements

A two-story building was proposed within the Port of Los Angeles' (POLA) Pier 400 site, which was created by hydraulically placing dredged materials contained by perimeter dikes. The close proximity of the building to the dike could result in significant vertical and lateral movements of the ground surface during a design earthquake due to lateral spreading of the dike. A dynamic, two-dimensional, finite-element analysis performed near the site indicated that the lateral spread at the ground surface could be large near the edge of the building footprint during the design seismic event. The use of shallow foundations on improved ground was not permitted as the reviewing agency for the building design, the City of Los Angeles Department of Building and Safety (LADBS), would not allow large movements of the shallow foundations or a floating mat foundation. The design team selected pile foundations and lateral pile analyses were performed to determine the bending moments and shear forces within the piles due to varying lateral spread of the liquefied hydraulic fill surrounding them. The lateral spread estimates were made using simplified Newmark analysis, and an iterative scheme developed whereby shear forces developed in the pile were used to estimate the "pinning" effects of the piles, which were in turn added to the residual shear strength of the hydraulic fill. The total number of piles needed to reduce the lateral spread was determined so that the maximum moment within a pile would remain within its elastic limit, as required by the LADBS. The design procedure took advantage of pile pinning effects through the use of a simple analytical approach to achieve the project goals and gain acceptance by the LADBS.