Define relative compaction

Relative compaction (RC) is the ratio of the dry unit weight (density) achieved in the field to the maximum dry unit weight obtained in the laboratory compaction test (Proctor test), expressed as a percentage:

$$RC = \frac{\gamma_{d,field}}{\gamma_{d,max,lab}} \times 100$$

It is used as the field control of compaction. Specifications normally require RC of 95% (standard Proctor) for embankments and 98 - 100% for pavement layers or the top of fills. Not to be confused with relative density $D_r$, which is for cohesionless soils.