Case Studies of Pile Foundations Undergoing Lateral Spreading in Liquefied Deposits

M. Cubrinovski

Kiso-Jiban Consultants, Tokyo 102-8220, Japan

K. Ishihara

Chuo University, Tokyo 112-8551, Japan

Proceedings: 5^th lnternational Conference on Case Histories in Geotechnical Engineering, New York, NY, April 13-17, 2004.

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.

Liquefaction of surrounding soils during earthquakes may affect the performance of pile foundations leading to damage and even collapse of piles. In fact, there are cases of liquefaction related damage to piles caused by an excessive lateral movement of the liquefied soils. Generally speaking, two different phases in the pile response have to be recognized: one is the response of piles in the course of cyclic ground movement, and the second is the pile response during the subsequent lateral spreading of the liquefied soils. This paper highlights the performance of pile foundations in liquefied deposits based on a well-documented case history from the 1995 Kobe earthquake.

The investigated oil-storage tank is supported on piles and has a 4 m wide belt of improved soil around the perimeter of its foundation. During the Kobe earthquake, the fill deposit surrounding the foundation of the tank developed liquefaction. The quay wall, located about 20 m west of the tank, moved seawards and consequent lateral spreading of the backfill soils affected seriously the piles supporting the tank. Observations from detailed field survey of the ground and inspection of the damage to the piles are first presented in this paper, followed by results of analyses for the pile undergoing lateral spreading of the liquefied soils.

References

Japan Road Association, 1980: Specification for road bridges, Vol. IV (in Japanese).

Ishihara, K., Yoshida, K. and Kato, M. [1997]. “Characteristics of lateral spreading in liquefied deposits during the 1995 Hanshin-Awaji Earthquake,” Journal of Earthquake Engineering, 1(1): 23-55.

Cubrinovski, M. and Ishihara, K. [2003]. “Simplified method for analysis of piles undergoing lateral spreading in liquefied soils,” submitted to Soils and Foundations.

Cubrinovski, M. and Ishihara, K. [2002]. “Pile response to lateral spreading of liquefied soils: Demand-Capacity Method” Proc. U.S.-Japan Seminar Seismic Mitigation in Urban Area by Geotechnical Engineering, Anchorage, Alaska, CD-ROM.