Effects of fines on the cyclic liquefaction behaviour in unsaturated, well-graded materials

The liquefaction of cargoes of metallic ores during maritime transportation is believed to have caused a number of ships to capsize during the past 30 years. To minimise the risk of liquefaction, shipping standards specify a transportable moisture limit (TML), which is the maximum moisture content for ore cargoes to be loaded onto a ship. However, the mechanics leading to the liquefaction of these cargoes is not well understood. This study uses an unsaturated soil mechanics perspective to understand the cyclic liquefaction behaviour of partially saturated materials, similar in grading to iron ore fines, a metallic ore that is known to liquefy during shipping transportation. Iron ore fines are transported at relatively low densities and have variable gradings containing a wide range of particle sizes and fines contents. Therefore, the effects of the degree of saturation and the fines content on the cyclic liquefaction behaviour of well-graded materials have been investigated by performing unsaturated, compression-only cyclic triaxial tests on samples prepared with four different gradings containing particle sizes from 9.5 mm to 2 μm with fines (<75 μm) contents of 18%, 28%, 40% and 60%. The trends in the data are discussed and used to develop a simple method that can conservatively estimate the number of cycles that samples with different degrees of saturation and fines contents are able to resist. The use of this method to describe the liquefaction behaviour of cargoes containing iron ore fines, in practice, is discussed.