Maximum dry bulk density decreased with increasing clay, expanding minerals and organic matter content, whilst corresponding critical moisture contents (CMC) increased (Table 2). The percentage increase in bulk density when compared to in-situ values, varied from 11.6% in River Estate to 166% for the peaty clay. The greater compactability of peat [27] allowed for a significantly greater amount of material to be used during compaction. In this study a compactive effort of 549 kJ·m−3, equivalent to 25 compaction blows with the standard Proctor hammer [28] resulted in true changes in bulk density at moisture contents well below the plastic limit. The data indicates that all soils are prone to compactive levels