Liquefaction of Bulk Cargo and its Prevention

为了船舶运输的安全，散货必须防止移位和液化。液化发生时，货物的水分含量大于一个特定的值，称为流动水分点（FMP）。虽然已经提出了几种测定方法，但对于矿物精矿、类似材料和煤，没有一种方法是万能的。在本项目中，对液化现象进行了理论和实验研究，并提出了一种名为“渗透法（PM）”的新方法，并将其提交给国际海事组织，以纳入《BC规则》。对于散装货物，检测残余抗剪强度是判断液化是否发生的最方便的方法。PM的操作步骤如下：(1)将已测定水分含量的样品放入圆柱形容器中；(2)在试样表面设置穿透钻头；(3)垂直振动容器，加速度大于3G；(4) 6分钟后测量穿透深度；(5)当渗透深度小于某一特定值时，试样含水率大于FMP。该程序用几种精矿和煤进行了检验，得出的结论是，PM不依赖于操作人员的技能，结果的可重复性是足够的。需要强调的是，这种方法可以适用于高粘性材料。通过三轴循环压缩试验，测定了煤在饱和和非饱和条件下的液化强度。结果表明，煤饱和时的应力比为0.15，煤不饱和时的应力比为0.15的2倍。在货舱内，与滚动运动周期相对应的外力频率较慢，使得超孔隙压力有可能向表面消散，货物的液化强度无形中增大。在其他情况下，孔隙空气压力可能会降低液化强度，这取决于渗透性。在该程序中，还对矿物精矿和煤的渗透性进行了实验研究。少

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