A Study of Pile Fatigue Failures in the Arabian Gulf

Abstract

In the summer of 1974, construction commenced for an oil tanker terminal in the Arabian Gulf. The following winter, a particularly strong tropical storm hit after the piles were driven, prior to installation of the superstructure. Without the superstructure, the piles were lacking in lateral support and, as a result, two of the piles failed at the mudline due to fatigue. After further investigation, two other piles were determined to have suffered through-thickness fatigue cracks. These events triggered studies to ensure that further fatigue issues would not follow in the replacement piles, as well as to explain the fatigue failure mechanism. The studies outlined the following two topics. First, the motion response of cantilever piles in the ocean. As the piles were not yet supported by the superstructure, they were subjected to additional forces and the freedom to bend in ways that may have caused overstressing at the mudline. The next area of study was the fatigue damage due to cyclic stress associated with motion response. Essentially, the repetitive motions of the waves may produce a cyclic motion in the piles, causing repetitive stress at the same point, namely the mudline in this case. This report will utilize this situation as a case study to discuss the failure that occurred in the piles and why. An introduction to pile design and the various construction methods will be outlined, as well as an overview of the studies performed and their results.