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Imported chalk materials used as backfill must comply with the following requirements:
  1. The saturation moisture content must be determined before use.
  2. The chalk must be laid and compacted to an approved compaction procedure developed in accordance with NG1.6 (4) and A9. The compaction procedure must be proven with chalk materials of similar saturation moisture content.
Excavated chalk to be re-used as backfill must comply with the following requirements:
  1. Excavated chalk must be stockpiled for re-use and must not be subjected to multiple handling.
  2. During wet weather, excavated chalk must be protected against water ingress at all times.
Chalk materials must be assessed by breaking up excavated fragments by hand or by driving a steel pin into unexcavated deposits, and classified in accordance with Table S5.1. If the classification falls between two densities, then the chalk must be assumed to be at the lower of the two densities.
Table S5.1 Suitability of chalk materials for use as backfill

Chalk density

Physical assessment

Backfill suitability


Very difficult/impossible to break up by hand
Difficult to hammer in steel pin.

Carriageways, footways and verges.


Some difficulty in breaking up by hand.
Some effort needed to hammer in steel pin.

Footways and verges only.

Easy to break up or crush by hand.
Steel pin can be pushed in by hand.

Unsuitable for use in any reinstatement.
Chalk often contains flint inclusions and care should be taken to ensure that:
  1. the steel pin does not strike a flint
  2. the hand crushing sample does not contain any flints.
Chalk materials must be compacted in accordance with A8.2.