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3) Settling and consolidation columns
To mimic (partly) mimic the conditions at sea, the tailings are placed in 1m high columns. For every sample an expected minimum and maximum concentration is used. The material is mixed and for 3 weeks the experiment was recorded by an automated camera (Figure 4).
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After settling the material will start to consolidate and the strength of the bed will increase. The strength of the bed determines the sensitivity to erosionre-suspension and possible dispersion of the tailings . At three moments in time the strength of the bed is measured by Vane testsvane tests. A vane is a rotating rod with 4 blades at the end. The soil resistance to rotation is a measure for the strength. Figure 5 shows an illustration of the device and an results of sample 47.
Figure 5: Left: Vane test, Right: Result of measures peak shear strength
The strength of the bed was measured after 20 hrs, 1 week and 3 weeks of settlement. The results are shown in Figure 7. As can be seen, there is an rapid increase in strength in the first week. After this week the rate of increase decreases. This is according to theory. Thereafter there are some samples with a lower strength in week 3 compared to week 1. Probably this is due to artifacts.
