Foundations · Footing settlement
Layered settlement under a rectangular footing (Fadum + oedometer) calculator
Stress increase at the centre of each layer by the Fadum influence factor, the layer settlement Δσ·h/Eoed, the total and the depth where Δσ falls below 20 % of σ′v.
Standard: Elastic stress (Newmark/Fadum, centre) · oedometric modulus per layer · 20 % σ′v influence depth
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Footing width B | 2.5 | m |
| Footing length L | 3 | m |
| Net applied pressure | 120 | kPa |
| Founding depth | 1 | m |
| Unit weight above base | 18 | kN/m³ |
| Layers below base: thickness (m), γ′ or γ (kN/m³), Eoed (MPa) | 1.5, 18, 20 2.0, 9, 12 2.5, 9, 15 3.0, 10, 30 4.0, 10, 50 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Depth of influence counted (Δσ ≥ 0.2σ′v) | 6.00 | m |
| Check: depth of layer data | 13.00 | m |
| Total settlement (layers with Δσ ≥ 0.2σ′v) | 18.55 | mm |
- ✓ Settlement ≤ 25 mm
- ✓ Layers extend below the influence depth
Method, formulas and assumptions
- Depth of influence counted (Δσ ≥ 0.2σ′v) = MAX([t.zc]) = 6 m
- Check: depth of layer data = SUM([t.h]) = 13 m
- Total settlement (layers with Δσ ≥ 0.2σ′v) = SUM([t.s]) = 18.55 mm
- Use buoyant unit weight below the water table. Immediate plus primary settlement from Eoed; add secondary compression for organic or soft clays.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.