Evaluation of liquefaction potential of bulk materials
(Summary of the Result of the Research Project)
1 Introduction
For the purpose of development of the procedure for evaluating liquefaction potential of solid bulk materials, Nippon Kaiji Kentei Kyoukai (NKKK) and Ship Research Institute, Ministry of Transport (SRI) conducted a three year cooperative research project. The research project was coordinated by a committee in NKKK. chaired by Professor T. Ura, Institute of Industrial Science. University of Tokyo.
Through the research, the comprehensive procedure for evaluating liquefaction potential introduced in ANNEX 1 was developed. In this ANNEX the background for the determination of the criteria and the test procedure is presented.
Since it is clear that a material which does not contain fine particles is not liable to liquefy, the comprehensive procedure includes the judgment based on grain size distribution.
2 Liquefaction potential test
The developed procedure of liquefaction potential test and its basic idea are presented in ANNEX 1 . Here, the basis for determining consolidation procedure, period for vacuuming, period for drainage etc. are explained based on the results of the experiments.
The liquefaction potential test was applied to two slags, i.e., nickel slag (N.S.) and copper slag (C.S.) in various grain size distributions. They are residues of the smelting process for obtaining ferro-nickel and copper, respectively. The test was also applied to materials of which the Flow Moisture Points (FMPs) were measured, to confirm the consistency.
The test procedure is not applicable for coals or other materials having low solid density, e.g., less than 2,000 kg/m3, because the applicability of the Proctor/Fagerberg method is limited as pointed out in the BC sub-committee. (BC30/5/2 "Determination of flow moisture point" by Japan).
2. 1 Consolidation procedure
In ordinary Procter C consolidation procedure, the number of droppings of the hammer is 25 and the amount of the material for each layer is about 200 cm3. To apply the same compaction energy per unit volume, the number of droppings of the hammer for each layer in the liquefaction potential test was determined as 50, because the amount of the material for each layer is about 400 cm3 (refer to step B-9).
2.2 Period for vacuuming
Conceming thc step B-1, the material should be dried prior to insertion into the vessel in order to obtain low pressure in a short vacuuming period.
By using the vacuum pump of which the capacity was 100 litters/minute - 300 W, 1 5 minutes was enough for Obtaining a low pressure less than 100 Pa, i.e., one the thousandth of the ordinary air pressure. Figure I shows an example of the relation between vacuuming time and the inner air pressure of the vessel. Then, the period for vacuuming was determined as 15 minutes and the above specification of pump is recommended (refer to step B-10).
2.3 Period for drainage
Two examples of the relation between time for drainage and weight of drained water are shown in Figure 2. It can be said that 30 minutes is enough for the period for drainage for coarse materials through the drain hole of 3 . I mm diameter. Then, the period for drainage of
