Basement excavation = (length + 2 × working space) × (width + 2 × working space) × depth. A 20 × 15 m basement 3.5 m deep with 1 m working space is 22 × 17 × 3.5 = 1,309 m³: 1,636 m³ loose, 164 loads of 10 m³, about 3 days at 60 loads a day.
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Basement Excavation Calculator
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Basement excavation (bank)
1,309m³
Loose volume to haul
1,636.25 m³
Truck loads
164 loads
Haul duration
3 working days
Dig footprint
22.00 × 17.00 m
Retained face (shoring / piling area)
273 m²
Excavations deeper than about 1.2–1.5 m (4–5 ft) need sloping, benching, shoring or a trench box under most safety rules.
Basement excavations usually need a temporary works design for shoring, dewatering and neighbouring structures.
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Formulas
Footprint = (L + 2s) × (W + 2s)Volume = footprint × D (prismoidal if battered)Retained face = 2 × ((L + 2s) + (W + 2s)) × D (vertical sides)Haul days = ⌈truck loads ÷ loads per day⌉
Worked example
A basement 20 × 15 m, 3.5 m deep, 1 m working space, shored vertical sides, common earth, 10 m³ trucks, 60 loads a day:
Basements need temporary works design for support, dewatering and nearby structures.
Frequently Asked Questions
How much soil comes out of a basement?
Multiply the dig footprint (basement plus working space) by the depth to the underside of the blinding. Then add 20–40% for swell to get the loose volume you will haul away.
How much working space does a basement need?
Often 0.6–1.0 m around the walls for formwork, waterproofing and drainage. With shoring and blind-side waterproofing it can be close to zero.
What is the retained face area?
The perimeter of the dig × its depth: the area of sheet piles, secant piles or soldier piles needed when the sides are vertical.
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