ARTICLE Slope stability evaluation of iron ore fines during marine transport in bulk carriers Michael C. Munro and Abbas Mohajerani Abstract: A commodity, such as iron ore fines, shifting in the hold of a bulk carrier can lead to the vessel listing or capsizing. The objective of this study is to investigate the factors of safety pertaining to slope failure for both untrimmed and trimmed cargoes of iron ore fines during marine transportation. To determine the shear strength parameters needed to perform this analysis, triaxial testing was performed on samples of iron ore fines under varying densities and moisture contents. Using the shear strength parameters of the material, the Morgenstern–Price method of slices and infinite slope analysis, referred to as rotational and translational slope stability analyses, were used to determine the factors of safety against slope failure. The study concludes that, considering a factor of safety of 1.5, an untrimmed cargo of iron ore fines is unstable at angles of heel that bulk carriers are expected to experience during a typical voyage. If the cargo is trimmed it is shown to be significantly more stable. Results support the recommendation that it become mandatory for cargoes of iron ore fines to undergo trimming to reduce the chance of slope failure occurring, which may result in the loss of human life and industry assets. Key words: iron ore fines, cargo shift, factor of safety against slope failure, triaxial testing, marine transportation via bulk carrier. Résumé : Une substance utile, telle que des fines de minerai de fer, qui se déplace dans un vraquier peut s’incliner ou provoquer le chavirement du navire. L’objectif de cette étude est d’étudier les facteurs de sécurité liés a ` l’insuffisance des pentes pour les cargaisons non taillées et taillées de fines de minerai de fer pendant le transport maritime. Afin de déterminer les paramètres de résistance au cisaillement nécessaires pour effectuer cette analyse, des essais triaxiaux ont été effectués sur des échantillons de fines de minerai de fer dans des densités et des teneurs d’humidité variables. En utilisant les paramètres de résistance au cisaillement du matériau, on a utilisé la méthode de Morgenstern–Price de tranches et l’analyse des pentes infinies, appelées analyses de stabilité des pentes de rotation et de translation, pour déterminer les facteurs de sécurité contre l’échec de la pente. L’étude conclut que, compte tenu d’un facteur de sécurité de 1,5, une cargaison non taillée de fines de minerai de fer est instable aux angles de talon que les vraquiers sont censés connaître lors d’un voyage typique. Si la cargaison est taillée, il est démontré qu’elle est sensiblement plus stable. Les résultats étayent la recommandation selon laquelle il devient obligatoire pour les cargaisons de minerais de fer de subir une coupe afin de réduire les risques de défaillance de la pente, ce qui peut entraîner la perte de la vie humaine et d’actif de l’industrie. [Traduit par la Rédaction] Mots-clés : fines de minerai de fer, inclinaison de fret, facteur de sécurité contre l’insuffisance de pente, essais triaxiaux, transport maritime par vraquier. Introduction A solid bulk cargo, such as iron ore fines, shifting in the hold of a bulk carrier can lead to transport vessel listing and possibly capsizing. Most incidents where cargoes shift during transporta- tion can be attributed to the occurrence of one of four distinct failure modes. Three of these failure modes, referred to as slope failures, can be seen in Fig. 1. All four failure modes relate to the reduction in shear strength between the particles of a solid bulk cargo. The first failure mode, liquefaction, is significantly more likely to occur in a cargo that contains sufficient amounts of fine parti- cles and moisture (International Maritime Organization 2013). Liq- uefaction occurs when there is a reduction in the shear strength and, therefore, the effective stress within a cargo. This can occur in the cargo either partially or as a whole, propagating rapidly from a single point of origin. Described in further detail in related publications (Munro and Mohajerani 2014, 2015, 2016a, 2016b, 2016c, 2016d, 2017; Munro and Mohajerani 1 ), liquefaction is more accurately described as “a phenomenon wherein a mass of soil loses a large percentage of its shear resistance, when subjected to monotonic, cyclic or shock loading, and flows in a manner resem- bling a liquid until the shear stresses acting on the mass are as low as the reduced shear resistance” (Sladen et al. 1985). The second failure mode, sliding en masse, occurs when the shear strength and friction along the stratum between the cargo and the hold is overcome by external forces and the entire cargo mass shifts as a single entity in the hold; thus, en masse. The third and fourth failure modes, herein referred to as rotational and translational slope failures, respectively, can occur when a slip plane develops due to the internal resisting shear strength of the cargo being exceeded by the resultant stresses being applied (i.e., equilibrium being overcome) (Budhu 2011; Das 2013). The consequence of all failure modes, if the transporting vessel acquires an asymmetric resulting moment, is one of buoyancy, Received 27 August 2016. Accepted 6 June 2017. M.C. Munro and A. Mohajerani. School of Engineering, Civil Engineering, RMIT University, Melbourne, Australia. Corresponding author: Abbas Mohajerani (email: dr.abbas@rmit.edu.au). 1 Munro, M.C., and Mohajerani, A. What is causing bulk carriers transporting iron ore fines to founder; liquefaction or shear failure? (Unpublished manuscript.) Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from RightsLink. Pagination not final (cite DOI) / Pagination provisoire (citer le DOI) 1 Can. Geotech. J. 00: 1–21 (0000) dx.doi.org/10.1139/cgj-2016-0468 Published at www.nrcresearchpress.com/cgj on 11 July 2017. Can. Geotech. J. Downloaded from www.nrcresearchpress.com by 115.70.206.243 on 01/04/18 For personal use only.