Secondary consolidant examples

Bjerrum (1972) presented Figure 8.19 in which he proposed that the secondary consolidation over a protracted period of time results in an apparent overconsolidation. In the example that he showed, the apparent overconsolidation would therefore be the difference between and as shown in the following equation ... 

If the organic content of a soil exceeds 20% by weight, consolidation becomes increasingly dominated by the behaviour of the organic material (Berry and Poskitt, 1972). For example, on loading, peat undergoes a decrease in permeability of several orders of magnitude. Moreover, residual pore water pressure affects primary consolidation, and considerable secondary consolidation further complicates settlement prediction. 

This potential for consolidation in the area of documentation systems was used as an example to sell the overall integration concept. Documentation was an area of constant complaint and senior management could easily visualize opportunities for improvement in basic resource requirements, as well as secondary effects on resources for training, auditing and other activities. Exhibit 10-1 was a key part of the presentation that the VP, ESH made to senior management. 

A typical plot illustrating the slow decrease in flux that can result from consolidation of the secondary layer is shown in Figure 31. The pure water flux of these membranes is approximately 200 L/min, but on contact with an electrocoat paint solution containing 10-20% latex, the flux immediately falls to about 40-50 L/min. This first drop in flux is due to the formation of the gel layer of latex particles on the membrane surface, as shown in Figure 30. Thereafter, the flux declines steadily over a 2-week period. This second drop in flux is caused by slow densification of the gel layer under the pressure of the system. In this particular example the densified gel layer could be removed by periodic cleaning of the membrane. When the cleaned membrane is exposed to the latex solution again, the flux is restored to that of a fresh membrane. 

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