Engineers Australia

A soil mechanics study into the liquefaction of shipped metallic ores

Katherine A. Kwa

Abstract

The transport of iron ore and other metallic ores by sea has been of increasing concern in recent years as several ships, their valuable cargo and around 200 lives have been lost because of liquefaction of the cargo. This has led to extensive soil mechanics based testing and analyses into the behaviour of iron ore fines during shipping transportation. In particular, the use of the Transportable Moisture Limit (TML), the maximum allowable moisture content based on a modified Proctor Fagerberg Test (PFT) at which a material is designated as being at risk of liquefaction when loaded into bulk carriers, has attracted considerable interest. The International Maritime Solid Bulk Cargoes (IMSBC) Code has categorised iron ore fines as a problematic cargo, prone to liquefaction because of the presence of moisture as well as fines in the material. The IMSBC code uses the TML to prevent liquefaction of the cargo, however, the rationale behind using the TML has been questioned.

This study investigates the influence of fines on the mechanics behind the liquefaction of well graded materials with similar gradings to iron ore fines that could be expected to liquefy during shipping transportation. The results so far show that as the fines content is increased, the density achieved during the loading of the material onto the ship decreases. However, results from cyclic triaxial tests suggest that density alone is not a good indicator of how resistant a material is to cyclic liquefaction. Using the state parameter gives a better understanding of the overall behavioural trend of the materials when subjected to cyclic loading conditions. The influence that these findings and results from preliminary unsaturated cyclic triaxial testing has on understanding the liquefaction behaviour of ship cargoes, will also be discussed.