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HAUC

Structural layer thickness tolerances (A2.7)

A2.7.1
Several individual layers of material, commonly termed lifts, may be required to reinstate a structural layer.
A2.7.2
The thickness of each complete structural layer is specified as a nominal value.
A2.7.3
The lower tolerance for the thickness of a structural layer must be as follows:
  1. -5 mm for the surface course
  2. -10 mm for any other structural layer comprising bound material
  3. -20 mm for any other structural layer comprising unbound material
A2.7.4
There is no upper tolerance for structural layer thickness. However, where large thicknesses of surface course are used:
  1. the requirements for compacted lift thicknesses under A2.8 must be met as must the in-situ air-voids through the full depth of the as-laid surface course layer, as set out in S10.2.8.
  2. the required combined binder and base course material thickness is still required unless the binder course mixture is replaced with surface course mixture, as permitted by A2.0.4 and A2.0.5.
  3. the surface profile performance requirements set out in S2.2 must not be exceeded.
A2.7.5
Any combination of permitted tolerances for the thickness of each structural layer of bituminous or cement bound mixtures must not result in either of the following:
  1. An overall reduction in thickness of the bound pavement, excluding the sub-base, of more than 15 mm from the specified nominal thickness in a road, subject to an absolute minimum of 100 mm of bound materials. See S6.8.9(2) for an exception to this requirement where only the surface is trimmed.
  2. An overall reduction in the thickness of the bound pavement, excluding the sub-base, of more than 10 mm from the specified nominal thickness in a footway, subject to an absolute minimum of 60 mm of bound materials. See S8.6.3 for an exception to this requirement where only the surface is trimmed.
A2.7.6
If the combined thickness of the relevant layers equals or exceeds that of the Code requirements, then this will not be considered as a non-compliance with the Code provided that each individual lift meets the thickness requirements of Tables A2.5 and A2.6 and the bituminous mixtures meet the void requirements of S10.2.8.