Figure 3.8 Illustration of soil horizons. In this frame, the soil horizons are very distinct and show the
geological history of the soil.
3.4.4 Back Filling the Hole after the Probes are Installed.
After soil is removed from the ground and piled up next to the hole, the horizons and soil
become physically homogenized. The bulk density decreases considerably because the soil
structure has been disturbed. After the probes are securely installed into the wall of the pit, the
pit needs to be backfilled with the soil that came out it. It is impossible to put the horizons back
the way they have formed naturally, but the original bulk density can be approximated by
compacting the soil. For every 24 cm (1 foot) of soil put back into the pit, the soil should be
compacted. Compaction can be done by trampling the soil with feet and body weight.
Mechanical compactors can also be used, though typically they are not required. Extra care must
be taken not to disturb the probes that have exposed heads, cables and conduits when compacting
the soil. If the probes were installed in a post hole, a piece of wood, such as a post, can be used to
pack the soil.
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