Groundworks are where estimates most often slip, because so much of the cost sits below the surface and outside the drawings. Accurate groundworks estimating starts with the site: existing and finished levels, soil type and the water table. From there you price the topsoil strip, then work out your cut-and-fill balance — the material you dig out that can be re-used as fill, which reduces both disposal and import.
The items that catch people out are the ones a drawing rarely shows: dewatering where groundwater is high, trench support and working space, compaction in layers, and disposal. Muck-away should be priced by the tonne and by the lorry load, and you must check soil classification and contamination testing before assuming clean disposal, because contaminated spoil costs far more to remove. Where cut and fill do not balance, imported fill such as 6F2 or Type 1 is priced delivered and compacted.
ConstructQS has a dedicated cut-and-fill calculator and an earthworks category built into the estimator, so bulking and compaction factors, disposal and import quantities are quantified rather than buried in a lump sum — and the AI QS assistant flags a missing muck-away or compaction allowance before you tender.