Swell & Shrink Factor Chart
The volume-change factors behind every earthwork estimate, in honest ranges: published swell/shrink factors carry an average ±33% variation (church 1981) — these are ranges, and the geotech report governs. Definitions are bank-basis (swell % = (loose ÷ bank − 1) × 100); the load-factor column converts truck yards back to pay yards.
Swell and shrink by material (bank basis)
| Material | Swell % (bank→loose) | Load factor | Shrink % (bank→compacted) |
|---|---|---|---|
| Sand, dry | 5–15 (typ. 12) | 0.89 | 10–12 |
| Sand, wet | 5–12 (typ. 5) | 0.95 | ~11 |
| Gravel, dry | 5–20 (typ. 13) | 0.89 | 2–8 |
| Sand & gravel mix | 12–14 (typ. 12) | 0.89 | ~12 (thin data) |
| Common earth / loam | 20–50 (typ. 25) | 0.80 | 10–20 |
| Topsoil | 43–56 (typ. 50) | 0.70 | 25–26 |
| Clay, dry | 20–50 (typ. 35) | 0.78 | ~10 |
| Clay, wet | 25–67 (typ. 40) | 0.71 | ~10 |
| Silt / silty clay | 30–36 (typ. 35) | 0.74 | 9–20 |
| Rock, well blasted | 50–80 (typ. 62) | 0.60 | −25 to −43 (net swell) |
| Limestone | 59–75 (typ. 65) | 0.59 | −31 to −36 (net swell) |
| Sandstone | 54–67 (typ. 61) | 0.60 | −29 to −34 (net swell) |
| Shale, weathered (soil-like) | 33–40 (typ. 35) | 0.74 | ~17 |
| Shale, blasted (rock-like) | 50–65 (typ. 55) | 0.65 | −25 to −33 (net swell) |
| Caliche | 16–82 — widest disagreement in print | 0.55 | ~25 (verify locally) |
| Asphalt pavement, broken | 49–50 (typ. 50) | 0.67 | ~0 (recompacts to bank) |
| Concrete pavement, broken | 50–72 (typ. 67) | 0.60 | −33 to −43 (never returns) |
Where each factor bites
Swell costs trucking: a 10,000 BCY cut at 25% swell is 12,500 truck yards — see the truck chart. Shrink costs borrow: 10,000 CCY of embankment at 12% shrink consumes ~11,364 bank yards. The full chain with worked math lives on the conversions chart, and the site-level consequences on the cut & fill reference. Weights ride along — the weight chart is this table's twin.
Common questions
What is a soil swell factor?
Swell % = (loose ÷ bank − 1) × 100 — how much a bank yard grows when excavated. Common earth at 25% swell turns one bank yard into 1.25 loose yards in the truck; the load factor (load factor = bank ÷ loose = 1 ÷ (1 + swell)) converts back. Trucks, buckets, and stockpiles all live in loose yards; the ground and most pay items live in bank yards.
What is the difference between swell and shrinkage?
Direction — and both measure from bank. Swell is bank-to-loose (excavation expands everything); shrinkage is bank-to-compacted (a roller packs most soil denser than nature did). Common earth swells ~25% loose and shrinks ~10–15% compacted. One warning: a competing convention measures the other way ("expand the fill"), and its numbers are not interchangeable with these — check any table's basis before mixing.
Does rock shrink when compacted?
Never. blasted rock and broken concrete placed as fill never compact below bank volume — plan on 25–43% more space than the cut — you cannot vibrate blasted rock back into the mountain. The chart shows those entries as negative shrink, and it is why balanced rock grading exports material while balanced earth grading imports it.
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