Field calculator
Soil swell and shrink calculator (excavation volume)
Dirt changes volume depending on its state, and getting that wrong throws off both the truck count and the fill. Soil in the ground is measured in bank cubic yards (BCY). Once you dig it, it loosens and takes up more room, measured in loose cubic yards (LCY), which is what you actually haul. Placed and compacted in a fill, it settles to less than its bank volume, measured in compacted cubic yards (CCY). Loose equals bank times one plus the swell percentage; compacted equals bank times one minus the shrink percentage. Enter the bank volume and the swell and shrink percentages for your soil. Swell and shrink vary widely by soil type and moisture, with sand, clay, and rock behaving very differently, so base a real estimate on load counts, compaction tests, or the geotechnical report rather than rule-of-thumb factors.
Result
Earthwork volume converts between three states: bank (BCY, soil in place), loose (LCY, excavated and hauled, larger because it swells), and compacted (CCY, placed in a fill, smaller because it shrinks). Loose = bank × (1 + swell%), compacted = bank × (1 - shrink%). Enter the bank volume and the swell and shrink percentages for the soil. Swell and shrink depend heavily on the soil type and moisture (sand, clay, rock differ a lot), so use load counts, compaction tests, or the geotechnical report rather than rule-of-thumb factors for a real estimate.
anvilfield.com/calculators/soil-excavation-swell-shrink-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
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Soil swell/shrink FAQ
What is proof rolling?
Proof rolling is a field test where a heavy loaded vehicle, often a 20 ton tandem dump truck, is driven slowly over the prepared subgrade or base while an inspector watches for pumping and rutting. It reveals soft areas that scattered density tests miss. Weak spots get undercut, recompacted, and re-proofed before building over them.
What is a Proctor test?
A Proctor test is the lab test that finds a soil's maximum dry density and the optimum moisture content that reaches it, by compacting the soil at several moisture contents and plotting the curve. Every field compaction target is a percentage of that lab maximum, so the Proctor is the yardstick the whole job is measured against.
What compaction do you need under pavement?
Aggregate base is commonly compacted to 95 percent of modified Proctor maximum dry density, with the subgrade often at 95 percent in the top layer and around 90 percent in deeper fill. These are typical figures only. The project geotechnical report and earthwork specification set the actual targets and say which Proctor applies.
Why does pavement fail from the base and not the surface?
The base carries the load and the surface only rides on it. A soft, wet, or under-compacted subgrade or base flexes too far under traffic, and asphalt that flexes too far cracks from fatigue. The cracks show on top because that is where you see them, but the cause is the moving foundation below.
Standard Proctor versus modified Proctor: which do I use?
Modified Proctor, ASTM D1557, uses roughly 4.5 times the compactive energy of standard Proctor, ASTM D698, giving a higher maximum dry density at a lower optimum moisture. Base and granular subbase commonly use modified; general subgrade sometimes uses standard. The spec names which one governs, and 95 percent of modified is a tougher target than 95 percent of standard.