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Field identification test No 4 – Granular grading

All unbound granular materials must be reasonably well graded i.e. they must contain a range of particle sizes from fine to coarse, with an adequate proportion of particles of intermediate sizes. A well-graded material can be compacted to give a dense and stable structure of interlocking particles with a low proportion of air voids within the structure.


Depending on the size of the stockpile, dig out representative samples from beneath the outer surface at several positions around the outside.

Test – Granular grading

Spread out each sample and examine under good light.


Class A graded granular materials – should not contain any particles greater than 75 mm nominal size and, in general, should be 50 mm or less. Smaller particles down to less than 5 mm nominal size should be present in gradually increasing numbers as the size decreases. Finer particles from sand size down to dust should be present and will usually be adhering to the larger particles. Fine particles should be visible adhering to around 30% or more of the surfaces of most of the larger particles.

Class B granular materials – should show the same general features as described above but will usually be less well graded overall compared with Class A Graded Granular Materials.

Class C Cohesive/granular materials – will usually contain a much larger proportion of fine material. The granular content should still be less than 75 mm nominal size, down to less than 5 mm nominal size and should not be single sized.