A buried tank is ordered from its inside size and the thicknesses of its walls and slabs. This guide counts quantities; the thickness against earth and water pressure, the reinforcement and the watertightness are the engineer’s.
1. Capacity and outside size
The capacity is the inside length times width times depth; one cubic metre is 1,000 litres. The outside length and width add two wall thicknesses.
2. Concrete, formwork and excavation
Walls: outside footprint minus inside footprint, times the depth. Floor and cover slab: the outside footprint times their thickness. Formwork covers the inside and outside wall faces and the underside of the cover slab. The excavation is the outside size plus the working space on each side, down to under the blinding.
Worked example: 4 × 3 × 2 m inside, covered tank
Walls and floor 20 cm, cover slab 15 cm, blinding 5 cm, 50 cm working space, 80 kg of steel per m³:
Capacity 24 m³ = 24,000 litres; outside 4.40 × 3.40 m = 14.96 m².
The count does not size the walls, check buoyancy or design the reinforcement. The steel ratio is a starting value: replace it with the figure of the engineer’s schedule.
General information, checked at the date shown. It does not replace advice from a professional for your situation.
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