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Earthwork & Soil Swell

Determine Bank Cubic Yards (BCY) vs excavated Loose Cubic Yards (LCY) to accurately estimate the required number of dump truck loads for site evacuation.

Pit Dimensions

Length

Width

Depth

Soil Stratigraphy Type

Undisturbed ground is extremely compact. Upon excavation, aeration introduces air pockets into the bulk dirt causing it to expand physically in the truck bed.

Payload Extraction Dynamics

Bank Yards (BCY)

222.2

yards³

Expanded

Loose Yards (LCY)

284.4

yards³

Swell Disturbance Metric	+28.000000000000004% volume
Equivalent 15-Yd Tandem Trucks	19.0 loads
Equivalent 22-Yd Semi End Dumps	12.9 loads

Logistics Danger: Many novice excavators bid jobs based purely on the physical hole dimension (BCY). They lose incredible amounts of margin paying hourly dump truck drivers to haul away the 'invisible' 30-40% volume expansion (LCY) that materialized once the heavy clay hit the air.

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What is The Earthwork Swell Phenomenon?

Undisturbed earth that has been compacted by gravity for ten thousand years is incredibly dense. When an excavator bucket violently rips it out of the bank, the solid chunks fracture into millions of pieces, injecting massive amounts of ambient air into the soil. This is known as 'Swell', and ignoring the mathematics of it is the number one way that new excavation contractors bankrupt themselves on commercial hauling jobs.

Mathematical Foundation

Geometric Bank Volume (BCY)

BCY = \frac{L \times W \times D}{27}

BCY

= Bank Cubic Yards. The literal volume of the physical hole in the ground.

L, W, D

= Length, Width, and Depth dimensions measured strictly in Feet.

27

= The mathematical constant converting cubic feet to cubic yards (3x3x3).

Aerated Swell Volume (LCY)

LCY = BCY \times (1 + S_f)

LCY

= Loose Cubic Yards. The expanded physical volume of the dirt after excavation.

S_f

= Swell Factor percentage (expressed as a decimal, e.g., 20 percent = 0.20).

Laws & Principles

The Pit vs The Pile Rule: The physical hole in the ground is measured in Bank Cubic Yards (BCY). The physical pile of dirt sitting next to the hole is measured in Loose Cubic Yards (LCY). They are never the same number. The LCY pile is always significantly physically larger than the hole it came out of.
Material Swell Extremes: Completely dry, fine beach sand experiences very little expansion (maybe 12 percent) because it is already a structurally loose material. Heavy, deeply-compacted wet clay, however, can physically swell by over 40 percent the moment it is aerated.
The Trucking Haul Limit: Standard tri-axle tandem dump trucks hold anywhere from 14 to 16 yards of material. Because they are loading aerated dirt with a front-end loader, you MUST divide your Loose Cubic Yards (LCY)—not your BCY—by the truck capacity to accurately bid hauling trips.

Step-by-Step Example Walkthrough

" A contractor bids a fixed price to dig a commercial foundation measuring 50 feet by 30 feet at a depth of 4 feet into a heavy wet clay field. They must haul all spoils offsite in standard 15-yard tandem dump trucks. "

1. Calculate the rigid geometric Bank Volume: (50 x 30 x 4) = 6,000 cubic feet.
2. Convert to Bank Yards: 6,000 / 27 = 222 Bank Cubic Yards (BCY) hole.
3. Apply Swell Factor: Heavy clay swells roughly 40%. Multiply 222 BCY x 1.40.
4. Calculate Aerated Pile Volume: The 222 yard hole creates an aerated pile of 311 Loose Cubic Yards (LCY).
5. Calculate Truck Loads: 311 LCY / 15 yards per truck = 20.7 Trucks.

Final Result: If the contractor blindly bid the job out based on hauling 222 yards of dirt (14.8 trucks), they would violently run out of fuel and driver-time budget. The dirt aerates and swells to 311 yards upon removal, demanding nearly 21 full tandem truck loads.

Quick Answer: How many cubic yards are in my excavation?

To find the cubic yards of the geometric hole, multiply the Length × Width × Depth (in feet) and divide by 27. This gives you Bank Cubic Yards (BCY). However, when you dig up the dirt, it expands by absorbing air. To find how much dirt you actually have to haul away in trucks, you must multiply your BCY by the soil's Swell Factor (usually adding 15% to 40%) to calculate your Loose Cubic Yards (LCY).

The Earthwork Equations

Hole Volume (BCY) = (L × W × D) ÷ 27

Haul Volume (LCY) = BCY × (1.0 + Swell Percentage)

Required Trucks = LCY ÷ Truck Capacity in Yards

Note: Always round fractional truck loads up to the next whole number. You can't order '0.6' of a dump truck haul.

Common Soil Swell Factors

Material Type	Characteristics	Swell %
Clean Sand / Gravel	Already loose, extremely granular	10% - 15%
Common Earth / Loam	Standard topsoil, moderate moisture	20% - 25%
Dry Clay	Hard packed, fractures into clods	25% - 35%
Wet / Heavy Clay	Sticky, massive clods, high air voids when piled	35% - 40%
Solid Rock (Blasted)	Massive angular boulders leaving huge air gaps	50% - 65%
Note: Using blasted rock as backfill is notoriously bad because the 65% swell factor indicates monumental amounts of empty air space that will eventually collapse.

Excavation Disasters to Avoid

The Shrinkage Deficit

A contractor calculates they need exactly 1,000 Bank Cubic Yards to build up a large retention berm. They buy 1,000 Loose Cubic Yards of dirt from a quarry and have it delivered. When they use a sheepsfoot roller to violently compact the loose dirt into the berm, they discover they are severely short. Loose dirt 'shrinks' when intentionally compacted. They should have ordered 1,300 Loose yards to guarantee they would achieve 1,000 compacted Bank yards.

The Water Weight Penalty

A crew leaves an excavated pile of 300 Loose Cubic Yards of clay sitting uncovered on site over a rainy weekend. They accounted for the swell, so truck capacity is correct. Unfortunately, clay absorbs water like a sponge. The pile physically absorbs 20 tons of rainwater. While the dirt volume (yards) matches the trucks, the trucks max out their highway weight scales before the bin is even full. They have to pay for 10 extra truck trips just to legally haul the massive wet weight.

Earthwork Pro Strategies

Do This

✓Account for angle of repose slopes. If you dig a 10-foot deep trench in sandy soil, OSHA requires you to slope the sidewalls back. A hole that was supposed to be 3 feet wide might physically become 15 feet wide at the top. The 'hole' is no longer a perfect rectangle, requiring complex trapezoidal math.
✓Tarp your stockpiles. A heavy duty tarp costs $100. Hauling saturated mud instead of dry dirt costs thousands in overweight truck fees and damages the subgrade of the site when trucks get physically stuck in the mud. Keep your dirt dry.

Avoid This

✗Don't mix topsoil and subsoil. The top 6 to 12 inches of a site is organic topsoil, highly valuable for landscaping but structurally worthless for compaction. If an operator mixes the topsoil into the deep clay subsoil, the entire pile becomes contaminated and cannot be used for structural backfill anywhere on site.
✗Don't rely strictly on visual counting. Many drivers are paid per load, incentivizing them to 'short load' the truck (putting 10 yards into a 15-yard truck). If you mathematically know the hole was 300 LCY, you should expect 20 trucks. If the trucking company bills you for 28 trucks, they are ripping you off.

Frequently Asked Questions

What does BCY vs LCY vs CCY mean?

BCY (Bank Cubic Yards) is the volume of the dirt while it is still undisturbed in the earth. LCY (Loose Cubic Yards) is the volume of the fluffy, aerated pile after excavation. CCY (Compacted Cubic Yards) is the final volume after you place the dirt in a new trench and aggressively pack it down with machinery. 100 BCY might swell into 130 LCY, and then shrink into 90 CCY.

Does my excavator bucket measure BCY or LCY?

All machinery attachments (excavator buckets, loader buckets) strictly hold Loose Cubic Yards (LCY). A 1-yard bucket cannot remove 1 Bank Yard of dirt per scoop because the dirt instantly swells the moment the teeth bite it. You must adjust productivity rates using the swell factor.

How do I calculate volume for sloped excavations?

A standard LxWxD formula only works for perfectly vertical walls. If the hole is sloped back for OSHA safety, it becomes a Frustum (a truncated pyramid). For complex sloped holes, engineers use the 'Average End Area' method or highly precise Prism volume formulas.

Are typical dump trucks limited by weight or volume?

It depends on the soil density and moisture. For dry mulch or loose topsoil, the truck will fill up physically (volume out) long before it hits the legal highway weight limit. For saturated heavy gravel or wet clay, the truck will exceed the legal limit (weigh out) while the bed is only half full.