Case studies of pile foundations undergoing lateral spreading in liquefied deposits

Abstract

A well-documented case study from the 1995 Kobe earthquake highlighting the performance of pile foundations in liquefied deposits undergoing lateral spreading is presented. The subject of this study is an oil-storage tank supported on 69 precast concrete piles, 23 m long and 45 cm in diameter. The tank is located in the west part of Mikagehama Island, about 20 m inland from the revetment line. During the Kobe earthquake, the fill deposit surrounding the foundation of the tank developed liquefaction. The quay wall moved seawards and consequent lateral spreading of the backfill soils affected seriously the piles supporting the tank. This paper presents results of detailed ground surveying depicting the ground distortion in the backfill soils and observations from field inspection of damage to the piles including bore-hole camera recordings and inclinometer measurements along the length of the pile. The piles were found to have suffered largest damage at depths corresponding to the interface between the liquefied fill deposit and the underlying non-liquefied soil layer. A simplified numerical analysis methodology was developed and used to perform the back-analysis for the piles damaged by the lateral spreading. The location and extent of the damage to the piles computed in the numerical analysis were shown to be in good correspondence with the actual damage observed in the field inspection of two piles of the tank foundation.