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8
In an earth fill, this zone of poor compaction would not be expected to be a problem since
the earth above might be expected to move downwards to fill the voids and consolidate
the ground. However, under the influence of rainwater and vibration, any spaces in the
soil immediately around, and especially under, the cell may grow, causing the cell to
become completely decoupled from the soil around it. In such situations, the internal soil
stresses go around the cell instead of through it. The cell will then register only a very
low pressure, which does not change much as the loads increase. This situation occurs
frequently.
2.2.1.1 Weak Grout Method
One way to avoid the problem is to cast the cell inside a weak grout. A method used
successfully in South Africa, by Oosthuizen et al, essentially uses the techniques similar
to the one described in Section 2.2.5. Installation of the cells begins when the fill has
reached a height of one meter above the instrument level. The Instrument location and the
cable trenches are excavated one meter deep, the instrument pocket, with 45° sloping
sides (Figure 10).
Figure 10 - Model 4800 Earth Pressure Cell Installation
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