Excavation Batter Calculator: Top Width, Volume, Bulked Spoil and Truck Loads
The geometry and quantities for a trench or pit with battered sides: batter angle, top width, volume, loose spoil and truck loads.
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How this calculator works
Enter the depth, the bottom width and the length of the trench. Enter the batter slope as the horizontal run for each 1 m of depth: 1 is a 45 degree slope and 0 is vertical sides.
The slope must come from the engineer, the soil report or the excavation code of practice. The calculator does not decide if a slope is stable.
Enter a bulking factor and the load carried by one truck to see the loose spoil volume and the number of truck loads. A message appears at 1.5 m deep or more, where extra ground collapse controls are usually needed.
Formulas used
- W_{top} = B + 2HD
- A = (B + HD)\,D
- V = A\,L
- \theta = \arctan\frac{1}{H}
Worked example
With the default numbers in the calculator above:
- Batter angle from the horizontal: 45.00 degrees
- Width across the top of the excavation: 5.00 m
- Cross-section area: 6.00 m2
- Volume of soil to remove (in the ground): 120.00 m3
- Volume of loose spoil (after bulking): 150.00 m3
- Truck loads of spoil: 25.00 loads
Change the numbers in the calculator to see the full working, every step, for your own case.
A second worked example
A different case, with these numbers: Batter slope: horizontal run for each 1 m of depth (0 is vertical sides) 0.
- Batter angle from the horizontal: 90.00 degrees (vertical sides)
- Width across the top of the excavation: 1.00 m
- Cross-section area: 2.00 m2
- Volume of soil to remove (in the ground): 40.00 m3
- Volume of loose spoil (after bulking): 50.00 m3
- Truck loads of spoil: 9.00 loads
Common questions
What is a batter slope?
A batter is a sloped wall of an excavation, laid back so the soil above is held up by the ground itself. It is described by how far it runs across for each metre of depth, for example 1 across to 1 down.
Why does the spoil volume come out bigger?
Soil swells when it is dug, so loose spoil takes up more room than the soil did in the ground. The bulking factor from the soil report allows for that and sets the number of truck loads.
When do I need shoring or a designed slope?
Extra controls for ground collapse are usually needed from 1.5 m deep. The soil, water, loads near the edge and nearby services all matter, so follow the excavation code of practice and an engineer.
Does this tell me an excavation is safe?
No. It calculates geometry and quantities from the slope you enter. Stability, shoring, access, water and services are separate checks.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: Excavation work Code of Practice (Queensland); Work Health and Safety Regulation 2011 (Qld), excavation work; your geotechnical report and engineer.
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