KEVOS® MAKEOS · Hydraulics
Buried or Submerged Tank Flotation Check (Uplift and Ballast)
Will this empty tank float out of the ground when the water table rises, and how much concrete ballast holds it down?
Flotation check of an empty buried or submerged tank: buoyant uplift on the displaced volume (as the buoyancy tool), resistance from the tank’s own weight, the submerged weight of the soil over it and the submerged weight of concrete ballast or an anchor slab, the safety factor against flotation, and the concrete mass needed to reach your required factor.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Volume displaced (tank outside volume below water) | m³ | Outside volume of the tank (and any attached structure) that can be below the water table. |
| Water density | kg/m³ | Density of the groundwater or flood water. |
| Tank mass (empty) | kg | Mass of the empty tank. |
| Plan area of soil carried on the tank | m² | Plan area of soil that sits on the tank and must lift with it. |
| Soil cover depth | m | Depth of soil cover over the tank. |
| Submerged unit weight of the soil | kN/m³ | Unit weight of the soil when below the water table (about 8–10 kN/m³; your value from the geotechnical report). |
| Concrete ballast or anchor slab mass | kg | Mass of concrete ballast, collar or anchor slab tied to the tank. |
| Concrete density | kg/m³ | Density of the concrete. |
| Safety factor required | Safety factor against flotation you require (often 1.1–1.5; follow your code). |
Method and formulas
- Uplift F_b = ρ_w g V (as the buoyancy tool).
- Resistance = tank weight + soil γ′ A h + ballast weight × (1 − ρ_w ÷ ρ_c) (the ballast is itself submerged).
- Safety factor = resistance ÷ uplift; ballast needed = (SF × F_b − tank − soil) ÷ [g (1 − ρ_w ÷ ρ_c)].
- Example: 10 m³ gives 98.067 kN of uplift; with 12000 kg of concrete the factor is 1.2905, and 11,305 kg would be needed.
Limitations
- Empty tank with the water table at the ground surface (worst case).
- Soil friction on the tank sides is ignored (conservative).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Design hold-down for a buried fuel or water tank
- Check a pit or sump for uplift
- Size a concrete anchor slab
Who it is for
- Civil engineers
- Plant engineers
- Design engineers
What you get
- Buoyant uplift
- Resisting weights and safety factor
- Ballast needed for the required factor
Interpreting the result
- Concrete only weighs about 58% of its dry weight under water: ballast must allow for its own buoyancy.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3027. Topic reference; no source tables or recommended settings are reproduced.
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Open the Buried or Submerged Tank Flotation Check (Uplift and Ballast) calculator
