The short version
- Soil has three volumes: bank in the ground, loose in the truck, compacted in the fill. Confusing them is the standard earthwork error.
- Swell governs haulage and truck counts. Shrinkage governs whether you import or export.
- A drawing that balances in bank volume will usually still need imported fill, because compacted material takes up less room than the ground it came from.
- Topsoil strip, unsuitable material and over-excavation are separate volumes and belong on separate lines.
Three volumes, one pile of dirt
Bank volume is the material as it sits undisturbed. Loose volume is the same material after excavation, when it has bulked up because digging introduces voids. Compacted volume is that material placed and rolled, which takes up less space than it did in the ground because compaction removes more voids than were there originally.
Every earthwork quantity is one of these three and it is meaningless without saying which. Excavation is priced in bank. Haulage is priced in loose, because that is what fills the truck. Fill placement is priced in compacted, because that is what the specification measures.
| Material | Swell, bank to loose | Shrinkage, bank to compacted |
|---|---|---|
| Topsoil | 25% to 35% | 10% to 20% |
| Sand, dry | 10% to 15% | 5% to 12% |
| Sand and gravel mix | 12% to 18% | 8% to 15% |
| Common earth or loam | 20% to 30% | 10% to 20% |
| Clay, dry | 25% to 35% | 15% to 25% |
| Clay, wet | 30% to 40% | 20% to 30% |
| Weathered or soft rock | 30% to 45% | Not typically used as engineered fill |
| Blasted rock | 50% to 70% | Placed as rock fill, factors differ by specification |
Why a balanced site still imports
Take a site with 10,000 cubic metres of cut and 10,000 of fill, both measured in bank volume from the sections. It looks balanced. It is not.
- You excavate 10,000 bank cubic metres.
- That material shrinks by, say, 15% when compacted, so it will place as 8,500 compacted cubic metres.
- The fill requirement is 10,000 compacted cubic metres.
- You are 1,500 compacted cubic metres short and you are importing, on a job the drawing said was balanced.
Meanwhile the haulage for that 10,000 bank cubic metres of cut is not 10,000 truck volumes. At 25% swell it is 12,500 loose cubic metres, which on a 15 cubic metre truck is 834 loads rather than 667. That is 167 loads nobody priced.
The volumes that are not cut or fill
A site earthwork estimate with only cut and fill lines is incomplete. These are separate operations with separate rates, and they need separate lines.
- Topsoil strip and stockpile, usually 150mm to 300mm across the whole site footprint, sometimes double handled
- Unsuitable material, which is a rate and an assumed quantity until somebody digs a trial pit
- Over-excavation below formation where the ground fails to compact
- Trench excavation, which is separate from bulk excavation and priced very differently
- Working space around foundations, which the drawing does not show and the method statement requires
- Backfill to trenches and around structures, often imported granular rather than site-won
- Disposal, which is a tipping cost plus a haul cost and moves with the waste classification
Disposal is the one that moves most. If any of the excavated material is contaminated, the tipping rate can be several times the clean rate, and the classification is not known until it is tested. That belongs in the estimate as a stated assumption with a rate against it, not as a silent inclusion in the excavation rate.
How we set it out
Every earthwork line carries the volume basis in its own column, bank, loose or compacted, and the swell or shrinkage factor applied to get there. The haulage calculation shows the loose volume, the truck capacity and the resulting load count, so the number of movements is visible rather than embedded in a rate per cubic metre.
It makes the sheet longer. It also means that when the geotechnical report arrives and the clay turns out wetter than assumed, changing one factor updates the haulage, the import and the disposal together.
Written by the estimating team at QuantX Estimation. Since 2016 we have measured and priced construction work for contractors in the United States and United Kingdom, at a fixed fee agreed before we start.
