An earthworks progress claim lands on your desk with a cut figure, a fill figure and a total. Your own number, or the one in the tender, doesn’t match. That doesn’t automatically mean someone has made a mistake.
Over 16-plus years in civil works across Dublin, London and Australia, I’ve found the two numbers have usually been measured against different surfaces, inside different limits, on different assumptions. And nobody wrote those down.
Measurement matters most where quantity drives payment: schedule of rates items, provisional quantities, remeasure items and variations. Under a lump sum the subcontractor generally carries the quantity risk, but variations still get measured. Here’s how I’d approach checking the number before you sign it off.
Why two parties get different numbers for the same work
A cut and fill volume is the difference between two surfaces inside a boundary, sometimes with a factor applied. Change any one of those and the number changes. These are the usual causes.
Different surfaces
- The base surface. Was it the natural surface from the tender survey, the stripped surface after topsoil came off, or a later re-survey? Some state road specifications, for example, measure general excavation from the stripped surface and pay topsoil stripping as its own item. Measure from natural surface and claim stripping as well, and the topsoil gets paid twice.
- The design surface. Comparing to finished surface level instead of subgrade or bulk earthworks level shifts every level by the pavement and topsoil depth. Cut comes out low and fill comes out high.
- What the progress survey picked up. Stockpiles, haul roads, parked plant and vegetation all end up in the surface if they’re surveyed.
Volume basis and factors
Bank, loose and compacted volumes are different numbers for the same material. One state road specification pays general earthworks on bank volume, imported fill on compacted volume measured in place, and topsoil kept on site on stockpile volume. In the volume tools I use, cut and fill factors default to 1 unless someone changes them, so ask what was applied. Any bulking or compaction factor should come from the subcontract, geotechnical advice or agreed testing, not a rule of thumb.
Limits, stages and exclusions
- Boundaries. Where do the limits sit? At the batter points? Are drains and rounding in? Where does one stage end and the next begin?
- Tolerances. Many specifications let tops of cut and toes of fill sit within a set tolerance outside the calculated batter lines. Some road specifications also leave level and batter tolerances out of the payment volume. Under those, digging below the design isn’t extra cut.
- Unsuitable material. Some specifications measure it separately, from surveys before and after removal, and only where removal was approved. Folded into general cut, it can be counted wrongly or twice. Whether material was unsuitable, and how much came out, is for the responsible engineer or Superintendent to decide under the contract, not the quantity check.
- Trenches and drainage. This excavation is often measured with the pipe and pit items, not bulk earthworks.
Survey quality and datum
- A surface built from sparse points, or without breaklines along kerbs, crests and batter tops and toes, lets triangles bridge across those features and misstates the shape.
- Public elevation data can’t stand in for the agreed existing surface. The national 5 m elevation model, for example, was built from surveys flown between 2001 and 2015 and broadly specified to around 0.3 m vertical accuracy at 95% confidence.
- Surfaces on different datums won’t line up. GDA94 and GDA2020 coordinates differ by over a metre. Check both sets of heights are on the same datum, normally AHD, not ellipsoidal heights or an unrecorded local datum.
- Net change adds up across successive progress surveys. Gross cut and gross fill don’t, wherever ground went up and then came down between surveys: stockpiles, haul roads, overfill that was trimmed.
Small level differences add up quickly. As an illustrative example with made-up figures, a uniform 20 mm difference between two surfaces over 10,000 m² is 200 m³.
What an independent check needs
- The design surface at the level the work is measured to, usually subgrade or bulk earthworks level, not finished surface.
- The existing surface used at tender, plus the stripped surface survey if there is one.
- The progress or as constructed survey, as a model file or as points and breaklines.
- The agreed limits and stage boundaries as closed polygons.
- The measurement clause and schedule items from the subcontract.
- Any agreed bulking or compaction factors.
- Approved unsuitable material records and the before and after surveys.
- The datum and coordinate system for every file.
Under the engineering manual used on many Victorian growth-area subdivisions, the construction plans show the extent and depth of fill, and the as constructed plans record fill areas, fill depths and finished levels. Those are useful cross-checks. Final lot levels are certified by a licensed surveyor, which is a separate job from a quantity check. AS 3798 deals with earthworks quality, inspection and testing, not with measuring quantities for payment.
How the comparison should be reported
A single total doesn’t help anyone. I’d report:
- Cut, fill and net for each stage or area, with the claimed figure and the check figure side by side.
- The volume basis (bank, loose or compacted) and any factors applied.
- Which surfaces were compared, and their survey dates.
- What was excluded: topsoil, unsuitable material, tolerances, trenches.
- The sign convention for net, so nobody reads a net import as a net export.
- A cut/fill depth plan, so you can see where the differences sit instead of arguing over a total.
Where the claim used a different basis, I’d run it both ways. That separates a disagreement about measurement from a disagreement about arithmetic. I set out how I prepare this kind of work on the earthworks takeoffs and cut and fill reports page.
Using the check with the subcontractor
Agree the surfaces and the basis first, then talk numbers. Once both sides accept which existing surface, which design level, which limits and which factors, whatever gap is left is much easier to discuss.
Raise datum or existing surface problems before the ground changes. One state road specification, for example, makes the Principal’s existing surface survey the basis for all quantities once the contractor accepts it, and a contractor who disagrees has to say so before the natural surface is disturbed. That’s sensible practice even where your subcontract is silent.
Watch the payment timeframe. Under Victoria’s Security of Payment Act, for example, a payment schedule is due within 10 business days of the payment claim, or sooner if the contract says so, and it has to give the reasons for paying less. So the check needs to be finished, and its reasons written into the schedule, inside that window. Other states have their own Acts. Check your contract and get advice.
Progress payments are commonly made on account, so an agreed correction can often carry into the next claim, depending on the contract. That can take some heat out of the conversation.
Keep the check in its place. It’s a basis for discussion, not a certified quantity. It doesn’t replace the surveyor, the Superintendent or the responsible engineer, and on its own it doesn’t settle a dispute.
What to send
- Design surface at subgrade or bulk earthworks level
- Tender or existing surface survey, and the stripped surface if there is one
- The subcontractor’s progress or as constructed survey
- Stage and area boundaries as closed polygons
- The claim and its calculation, if you have it
- Subcontract measurement clause, schedule items and any agreed factors
- Unsuitable material approvals and before and after surveys
- Datum and coordinate system details
If a claim on your desk doesn’t sit right, send the surfaces through and I can run an independent check against them.