How are irregularities in an unbound sub-base levelled?

Minor irregularities in an unbound sub-base are levelled with a compactable mineral aggregate. The aggregate consists of crushed rock and contains fines. Its grading is selected to suit the required correction depth.

High areas are cut back before the aggregate is spread in the lower areas, screeded to the required height and gradient, and compacted. After compaction, flatness and falls are checked and corrected where necessary.

Sand and chippings without fines are unsuitable because they cannot be compacted sufficiently and may migrate over time. Suitable gradings for the correction depth may include 0/8 or 0/16.