Laboratory scale reproduction and analysis of the behaviour of iron ore fines under cyclic loading to investigate liquefaction during marine transportation

Abstract

Specific hazards come with the transportation of solid bulk cargoes on bulk carriers. One unexpected hazard is the liquefaction of the cargo. Liquefaction is a phenomenon whereby cyclic or shock loading causes a commonly loose saturated material to flow like a liquid. Over the past 30 years, there have been 23 incidents in which liquefaction of the solid bulk cargo was the suspected cause of a bulk carrier foundering. The result from performing the Modified Proctor/Fagerberg Test (MPFT) on iron ore fines provides what is referred to as the Transportable Moisture Limit (TML). The TML is a safe moisture content under which a cargo is considered unable to liquefy while undergoing marine transportation. The objective of this study is to design and construct a scale model to test the conditions under which iron ore fines may liquefy, and to monitor the changes that occur within the material that may adversely affect the stability of the cargo during marine transportation. The parameters that are believed to influence the liquefaction potential of iron ore fines, including pore air and water pressures, moisture migration, segregation as well as other changes in physical properties, are monitored and compared to the behaviour at the TML determined from the MPFT. This study concludes that moisture migration, caused by an increase in the pore pressure within the material, also causes segregation of the material to occur. This process creates portions of the sample that are much more likely to liquefy than the sample as a whole. The moisture content where this begins takes place is 1.5% less than the resulting MPFT TML. Overall, it is considered that the TML as a parameter to indicate liquefaction is inadequate, as liquefaction is much more complicated and cannot be simplified in this manner.