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Coring and removal of large diameter cores

Before cutting the main core, a pilot core (not exceeding 100 mm diameter and located in the centre of the main core) must be taken to determine the depth of the bound layers (or the slab in an unreinforced concrete road). If the depth of the bound layers/concrete slab is less than 100 mm, reinstatement by core re-use is not permitted.
Temporary location and alignment marks should be made on the road surface before cutting the main core to ensure that it can be replaced in its original orientation. Care must be taken when cutting surface layers to avoid undue damage to the surrounding surface and binder course.
Large diameter coring must only be undertaken with purpose-designed equipment and in accordance with the manufacturer’s instructions. The cutter must be positioned perpendicular to the surface and extended to a depth that ensures that all the bound layers are removed as a single core.
Care must be taken to minimise dust and debris when core cutting. Water used for cooling the cutter must not contaminate water courses. Where the gradient or camber is significant, this must be considered as part of the overall site-specific risk assessment to ensure the operation can be safely completed.
Once the core has been removed, a further check must be undertaken to ensure that the depth of the bound layers is at least 100 mm around the full circumference of the core. If the depth is found to be less than 100 mm, reinstatement by re-using the core is not permitted.


  1. Excavation must be carried out in accordance with S3, of this Code. Material may be removed by conventional excavation methods or by air lance and/or vacuum excavation. Irrespective of the method of excavation, care must be taken to avoid undermining the adjoining structure.
  2. Where undermining of the adjoining structure does occur, reinstatement by re-using the core is not permitted and reinstatement must be carried out in accordance with S6.2, S6.3 and S6.4 or S6.5, as appropriate. This may require further excavation of the bound layers, in accordance with S3, to enable compaction of the underlying layers.