Iron Ore Liquefaction Susceptibility during Shipment

Abstract

The severe consequence of liquefaction after an earthquake event has been studied from many case histories in earthquake engineering, but the same liquefaction mechanism applied to the shipping industry of the shipping cargoes has not been well investigated and understood. The aim of this master thesis is to provide a basic understanding of the iron ores’ dynamic behaviour and a preliminary estimation of liquefaction susceptibility during the shipment. The cargo in the vessel can be arguably levelled into a flat surface to prevent liquefaction induced damage before shipping, but any additional time waiting in the port will cost extra millions of dollars. From the review of existing literature, the possibility of triggering a liquefaction failure is low, since not many liquefaction-induced accidents have been reported. Moreover, not many relevant documents were found to investigate this subject. Based on the methodologies of assessing liquefaction susceptibility of sandy materials in earthquake engineering, the entire research was separated into laboratory testing and liquefaction analysis. Three iron ores with very different index properties were evaluated from both fully saturated and partially saturated levels. Based on the cyclic resistance curves from the laboratory undrained triaxial test, a pseudo static analysis was carried out to evaluate the factor of safety (FoS) with corresponding rolling angle. Subsequently, a critical rolling angle of 5 degrees was defined. From the numerical modelling of the cargo stability, it showed the critical rolling angle was defined reasonably well, since all three ores were all above the benchmark under the specific shipping condition and motion. An additional centrifuge testing was performed, but a confident conclusion based on the limited results cannot be given at this stage. Notwithstanding, within a limited time frame, availability of the facility and equipment, lack of detailed parameters (sea wave, cargo geometry, type of motion, etc), a better simulation could not be achieved at this stage. In fact, ship motion is the most important parameter in this dynamic subject and rocking motion is the best simulation. There is no doubt that further analysis and investigation is essential to continue this subject.