Excavation volume determines how much soil must be removed for foundations, trenches, pools, and basements. It also drives equipment selection, trucking costs, and disposal fees.
Basic Formula
V = L × W × D (rectangular excavation). For trapezoidal trenches: V = [(W_top + W_bottom)/2] × D × L.
Swell Factor
Soil expands when excavated (swell). Clay: 30–40% swell. Sand: 10–15%. Rock: 50–70%. A 100 yd³ clay excavation produces ~130 yd³ of loose fill to haul.
Conversion
1 cubic yard = 27 cubic feet. Dump trucks typically carry 10–14 cubic yards per load.
Why Swell Factor Trips Up Budgets
Contractors who forget swell factor often under-budget hauling costs significantly — 100 cubic yards of in-place clay can swell to 130+ cubic yards once dug, meaning more truck trips (and disposal fees) than the original "hole size" volume suggests. This is one of the most common line-item cost overruns on excavation projects.
Compaction After Backfill
Confusingly, excavated soil that's later used as backfill compacts back down — often to 85–95% of its original in-place density, not 100%, since some structure of the original soil is permanently lost in the digging and re-placing process. This is why proper mechanical compaction (not just filling loosely) is required around foundations and utility trenches.