Liquefaction of Bulk Cargo and its Prevention

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Bulk cargoes should be prevented from shifting and liquefaction for the safety of transport by ships. Liquefaction occurs when the moisture content of the cargo is larger than a specific value which is called as the Flow Moisture Point (FMP). Though several methods have been proposed for its determination, no one is omnipotent for mineral concentrates, similar materials, and coals. In this program, the phenomenon of liquefaction is investigated theoretically and experimentally and a new method called the "Penetration Method (PM)" was proposed and submitted to the International Maritime Organization for inclusion in the BC Code. To judge the occurrence of liquefaction, measurement of residual shearing strength is the most convenient way for bulk cargoes. The procedure of the PM is as follows : (1)Put a sample, of which moisture content has been determined, in a cylindrial container ; (2) Set a penetration bit on the surface of the sample ; (3) Vibrate vertically the container with more … More than 3G acceleration ; (4) Measure the depth of penetration after 6 minutes ; (5) When the depth of penetration is less than a specific value, the moisture content of the sample is more than the FMP. This procedure was examined with several concentrates and coals, and it was concluded that the PM does not depend on the skill of the operator and repeatability of the result is sufficient. It should be emphasized that this method can be applicable to high cohesive materials.The liquefaction strength of coal was measured through the triaxial cyclic compression test in cases of saturated and non-saturated conditions. It is concluded that the stress ratio when the coal is saturated is 0.15 though it is twice larger when the coal is not saturated.In the cargo hold, frequency of external force, which corresponds to the cycle of rolling motion, is so slow that the excess pore pressure may dissipate to the surface and the liquefaction strength of cargo virtually increases. In other case, the pore air pressure may decrease the liquefaction strength depending of the permeability. In this program, permeability of mineral concentrates and coals are also investigated experimentally. Less