This can result from location on an uneven surface, such as near and over a reef structure, or near a growth fault, or from different susceptibility to compaction.

Through a series of testing data, the relationship of CBR with moisture content and compaction work is offered for the over-wet soil.

The formation of arch effects will bring the sand filling over the region of deep concavity hindered and the degree of compaction of molding sand at the deep concavity reduced.