Geotechnical Engineering

Relative Compaction

Field dry unit weight as a percentage of the laboratory maximum dry unit weight from a Proctor test.

Earthwork specifications commonly require fill compacted to at least 95% relative compaction. The field dry unit weight comes from a sand cone, nuclear gauge or similar test, converted from the wet unit weight by γ_d = γ/(1 + w); the maximum comes from a standard or modified Proctor test on the same soil.

Both numbers must be dry unit weights. Dividing a field wet unit weight by a laboratory dry maximum overstates the compaction, often to a figure above 100%, which should itself be a warning.

How much of the FE Civil exam is Geotechnical Engineering?