Shrinkage: Compacted Volume from Bank Volume

Shrinkage is swell's mirror image and it is the one that costs money. Material compacted into an engineered embankment at 95 % of standard Proctor density ends up denser than it was in the borrow pit, so a cubic yard of bank material fills less than a cubic yard of fill. Typical shrinkage runs 10–15 % for common earth and up to 25 % for organic or loosely bedded soils; rock is the exception, since blasted rock fills more than it occupied and is quoted as a negative shrinkage.

Every estimator's classic mistake is balancing cut against fill in bank measure and then discovering the job is short. A worked example: the plans call for 5,400 CCY of embankment in a soil with 10 % shrinkage. The borrow must supply 5,400 / 0.90 = 6,000 BCY — six hundred yards of imported material that a naive one-for-one balance would have missed. Chain the two factors together and you get the full life of a shovel of dirt: 1,000 BCY becomes 1,250 LCY on the trucks and 900 CCY in the finished embankment.