Example data table
| Scenario | Shape | Inside size | Wall height / freeboard | Tank volumes | Provided capacity | Concrete (with wastage) | Liner (with wastage) |
|---|---|---|---|---|---|---|---|
| Sample A | Rectangular | 10 m × 6 m | 1.2 m / 0.2 m | 12, 8, 5 m³ | 60.000 m³ | 6.867 m³ | 189.20 m² |
| Sample B | Circular | Ø 8 m | 1.0 m / 0.15 m | 20, 12 m³ | 42.726 m³ | 5.158 m³ | 158.39 m² |
Formula used
- Usable height = Wall height − Freeboard
- Provided capacity = Inside area × Usable height
- Required capacity = max( Largest×M, Total×T )
- Rain add = (Rain mm ÷ 1000) × Inside area
- Wall concrete = (Outer area − Inner area) × Wall height
- Base concrete = Outer area × Base thickness
- Liner area = (Base + Wall faces) × Layers × (1+Overlap)
- Adjusted = Quantity × (1+Wastage)
How to use this calculator
- Select the containment shape and length unit.
- Enter inside dimensions, wall height, freeboard, and thicknesses.
- Add container volumes as a comma-separated list.
- Choose the rule mode and adjust multipliers if needed.
- Set liner layers, overlap, wastage, and optional costs.
- Press Calculate to view capacity status and quantities.
- Use Download CSV or Download PDF for a report.
Containment capacity criteria
Secondary containment is sized from stored liquid volumes, not the wall dimensions alone. This calculator evaluates two common checks: the largest container multiplied by a safety factor, and a percentage of the total stored volume. The required capacity is the higher of those checks, then rainfall allowance can be added based on the inside footprint. Recording each container volume individually improves traceability and makes audits easier. Document the rule mode used so stakeholders understand why the target volume was selected today, clearly.
Geometry and freeboard impacts
Provided capacity uses inside area multiplied by usable height. Usable height equals wall height minus freeboard, so freeboard decisions directly change compliance margin. Rectangular bunds use inside length and width, while circular bunds use inside diameter. Because the wall thickness expands the outer footprint, concrete and excavation quantities respond strongly to thickness even when capacity stays constant.
Concrete takeoff interpretation
Concrete volume combines a wall ring and a base slab. The wall ring is computed from the difference between outer and inner areas, multiplied by wall height. The slab volume uses the outer footprint times base thickness, reflecting a continuous foundation under the wall. A wastage percentage is applied for batching losses and site variability, and an optional density converts volume to estimated weight for logistics planning.
Liner selection and overlaps
Liner area is calculated from the inside base plus inside wall faces, scaled by the number of layers. Overlap percentage accounts for seams, corner detailing, and anchoring allowances. If you specify a higher overlap or multiple layers, material requirements rise proportionally. For procurement, the wastage factor is applied after overlaps and layers, producing an ordering quantity that is typically closer to roll-based purchase realities.
Cost planning and sensitivity
Unit rates for concrete, liner, and excavation are optional but useful for early-stage comparisons. Costs are calculated on the adjusted quantities so the estimate includes overlap and wastage assumptions. To test sensitivity, vary wall thickness, base thickness, and freeboard: thickness drives concrete most, while freeboard mainly affects capacity. Exported reports provide consistent figures for reviews and vendor quotations.
FAQs
What is freeboard and why include it?
Freeboard is the vertical allowance below the wall top that remains empty. It reduces usable height to limit overtopping from waves, slosh, or rainfall. Increasing freeboard lowers provided capacity without changing the footprint.
Which rule mode should I choose?
Use “Use higher of both” for conservative sizing when you must satisfy multiple criteria. Choose “Largest only” if your standard is based on the biggest container. Choose “Total only” when your policy is a fixed fraction of stored volume.
Can I enter mixed container units?
Enter one unit type per calculation. Select the volume unit, then provide all container volumes in that unit. If your inventory is mixed, convert values first or run separate scenarios and compare results.
Why is liner area larger than the base area?
The liner covers the base plus the inside wall faces. The overlap percentage adds seam and detailing allowance, and multiple layers multiply the total area. Wastage then increases the ordering quantity for cutting and handling losses.
How does wastage affect ordering?
Wastage increases concrete, liner, and excavation quantities by a chosen percentage after geometric quantities are computed. It is intended for batching losses, trimming, and site variability. Set it lower for controlled projects and higher for complex layouts.
Does the calculator guarantee compliance?
No. It provides a consistent estimate using your inputs and selected rule parameters. Always verify assumptions, confirm local requirements, and have a qualified engineer review final designs, especially where hazardous liquids, slopes, or penetrations exist.