Earthwork: Bank, Loose, and Compacted — Why the Same Soil Has Three Different Volumes

A cubic meter of soil doesn't stay a cubic meter as it moves through a construction sequence. Undisturbed ground (bank measure) expands once it's dug up and loosened for hauling (loose measure), and compacted fill in place (compacted measure) is denser than the loose material that was trucked in to make it. Estimating haul trucks or borrow-fill quantities off the wrong volume state is one of the most common — and most expensive — earthwork mistakes.

Excavation: Bank to Loose, via Swell Factor

When soil is excavated, it expands as it's broken up and loaded for hauling. The swell factor — how much bigger the loose volume is than the bank volume it came from — varies by soil type: common soil swells around 25%, sand and gravel around 12%, clay around 30%, and rock as much as 50%. A 100 m³ bank excavation in clay produces roughly 130 m³ of loose material that actually needs to be hauled away — not 100 m³.

Fill: Compacted Back to Loose Borrow

Going the other direction — placing and compacting fill — works differently. Fajardo's fill-additional percentages describe how much extra loose borrow material is needed to achieve a given compacted volume, since compaction reduces volume from what was trucked in: roughly 24% additional for earth fill, 19% for earth-and-sand mixes, and 16% for selected borrow. A 100 m³ compacted-fill requirement means ordering around 124 m³ of loose earth fill to get there.

Sizing the Haul Fleet

Once loose volume is known (in either direction), converting to truck trips uses a standard haul truck capacity — typically around 8.0 loose m³ per trip for a standard dump truck. This is the number that actually drives the hauling line item in a BOQ, and it depends entirely on getting the bank-to-loose or compacted-to-loose conversion right first.

Structural Excavation Gets a Small Extra Allowance

Excavation for footings and other structural elements typically carries a working-strip or over-excavation allowance on top of the swell factor — commonly around 10% — to account for the extra working room a crew needs around the actual structural footprint, and for the reality that a neat, exact excavation to the design lines is rarely how it plays out in the field.

Worked Example: Sizing the Haul Fleet

A 100 m³ bank excavation in clay, swelling by roughly 30%, produces about 130 m³ of loose material that needs hauling. At a standard haul truck capacity of roughly 8.0 loose m³ per trip, that's 130 ÷ 8.0 ≈ 16.25, rounded up to 17 truck trips required — not the 12.5 trips a bank-volume calculation (100 ÷ 8.0) would suggest. That gap — nearly 5 extra truck trips on a modest 100 m³ excavation — is exactly the kind of shortfall that shows up as a real cost overrun once hauling starts and more trips are needed than were originally budgeted for.

Common Mistakes

The most damaging and most common mistake is sizing the haul fleet directly off bank volume — the number that's usually easiest to pull from the drawings — rather than converting to loose volume first using the appropriate swell factor for the actual soil type on site. Because swell factor varies meaningfully by soil (common soil around 25%, sand and gravel around 12%, clay around 30%, rock as much as 50%), applying a generic swell assumption instead of confirming the actual soil type can still leave a haul estimate short even when the estimator remembered to apply swell at all. The second common mistake runs the opposite direction on fill work — ordering borrow material against the compacted-fill target volume directly, without applying the fill-additional percentage that accounts for compaction reducing the loose material's volume once it's placed and compacted, which under-orders fill material in essentially the same way skipping swell factor under-counts haul trips on the excavation side.