Bank yards vs compacted yards: why the numbers never match on your pay app

Every super who has reconciled a haul ticket against an engineer's cut quantity has hit this wall. The cut says one number. The truck count says another. Neither is wrong. They're measuring the dirt in different states, and if you don't account for that, your pay app math will never close.

Bank yards: the dirt where it sits

A bank cubic yard (BCY) is soil measured in its natural, undisturbed state, still in the ground before anyone touches it. When your geotech report or your cut/fill takeoff gives you a cubic yardage for excavation, that number is almost always bank yards. It's the volume of the hole itself, measured before excavation starts.

The problem is that nobody hauls bank yards. The second an excavator breaks that ground, the soil structure opens up, air gets into it, and it takes up more space than it did in place. That's swell, and it's the first place your numbers start to drift from the bank quantity on the drawings.

Loose yards and the swell factor

Loose cubic yards (LCY) are what's actually sitting in the bed of a truck or in a stockpile. Swell factor is the percentage increase from bank to loose, and it moves with soil type. A clean sand might swell 10-15%. A heavy clay can swell 30% or more. Rock swells the most of all, sometimes 50-60%, which is exactly why rock excavation gets priced and hauled differently than common fill.

This is where load-count disputes start. If a sub is counting truck loads and converting back to bank yards using a swell factor that's a little generous, every load makes the cut volume look bigger than it is. Nobody's necessarily cooking the books. It's just an assumption baked into a conversion factor, and small assumptions compound fast over a few thousand loads.

Compacted yards and the shrinkage factor

Compacted cubic yards (CCY) are the dirt after it's been placed and rolled on the fill side, back to a density at or above what it had in the bank, sometimes higher if your spec calls for 95% or 100% standard Proctor. Shrinkage factor describes the relationship between bank yards and compacted yards: because compaction packs particles tighter than the soil's natural state, you generally need more bank yards of material than the finished compacted volume shows.

So on one job you're dealing with three different units for what sounds like "the same dirt": bank yards in the cut, loose yards on the haul, compacted yards in the fill. A rough rule some estimators use is cut yards times a shrink/swell factor roughly in the 0.85-0.95 range gets you to fill yards, but that range depends entirely on soil classification, moisture content, and compaction spec, and it's worth confirming against your geotech data rather than a generic chart.

Where this actually bites a pay app

None of this is academic once an owner's rep is sitting across from you asking why the haul tickets don't match the design cut. If your contract pays on in-place bank yards (common for unclassified excavation) but your field crew is tracking loose yards off truck counts, you need a defensible conversion, and you need it documented the same way every time, not adjusted mid-job when the numbers look tight.

That's really the argument for pulling your cut/fill volume straight off a surface-to-surface volume comparison rather than backing into it from a swell factor and a truck count. A quantity built from a surface comparison calculated off a weekly drone scan of the actual ground gives you a bank-yard number tied to the surface itself, independent of how much a particular soil fluffs up in the bed of a dump truck.

If your last few draws got argued over because the sub's load count and the engineer's cut quantity told two different stories, it's worth putting a surface-derived volume in front of the numbers instead.