Liquefaction Behaviour of Shipped Metallic Ores from a Soil Mechanics Perspective

Abstract

The transport of iron ore fines and other metallic ores by sea has been of increasing concern in recent years as several ships, their cargo and crew have been lost as a result of liquefaction of the on-board cargo. The mechanics behind the liquefaction of the cargo is not well understood and one of the main areas of uncertainty that is currently being studied is in understanding the soil mechanics behind the behaviour of the unsaturated ores when subjected to severe cyclic loading conditions that can develop during transportation. Shipping standards have also developed various procedures to prevent these hazardous cargoes from liquefying by defining the Transportable Moisture Limit (TML). This is the maximum allowable moisture content at which a material is designated as being at risk of liquefaction when loaded into bulk carriers. However, the rationale behind simply using a TML to prevent liquefaction of the material during transportation, has been questioned. This thesis uses a Critical State Soil Mechanics perspective to more rigorously understand the mechanics behind the liquefaction of materials similar in grading to the metallic ores that have been known to liquefy during shipping transportation. In particular, the influence of grading, fines content, density and degree of saturation on the cyclic liquefaction behaviour of these materials were experimentally investigated through performing saturated and unsaturated, monotonic and cyclic triaxial tests and small centrifuge tests. A fully coupled hydro-mechanical model was also calibrated and used to gain a better understanding of the effects of fines content and degree of saturation on the hydraulic behaviour of the materials. The findings and implications of the results on the liquefaction behaviour of ship cargoes, that have been obtained from this research project, will be presented and discussed in this thesis.