Foundations · Pile capacity
Pile axial capacity (layers, AS 2159 φg) calculator
Shaft and base resistance through layered sand (SPT N) and clay (su), with the AS 2159 geotechnical reduction factor and a resistance profile.
Standard: API α method (clay) · Meyerhof SPT (sand) · AS 2159 φg
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 |
|---|---|---|
| Pile diameter | 0.6 | m |
| Layers: thickness (m), S or C, N (sand) or su (clay, kPa), γ (kN/m³) | 3, S, 8, 18 6, C, 40, 17.5 4, C, 80, 18.5 5, S, 30, 20 | |
| Water table depth | 2 | m |
| Sand shaft factor ks (fs = ks·N kPa) | 2 | |
| Sand shaft limit | 100 | kPa |
| Sand base factor (qb = kb·N kPa) | 400 | |
| Base limit | 12000 | kPa |
| φg (AS 2159 Cl 4.3 risk assessment) | 0.55 | |
| Design action N* | 2200 | kN |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Pile length | 18.0 | m |
| Shaft resistance Qs | 1,299 | kN |
| Base resistance Qb (qb = 12,000 kPa) | 3,393 | kN |
| Ultimate Rd,ug | 4,692 | kN |
| Design Rd,g = φg·Rd,ug | 2,581 | kN |
| 0–3 m (S): fs, Qs | 16 kPa, 90 kN | σ′v 27 |
| 3–9 m (C): fs, Qs | 26 kPa, 293 kN | σ′v 67 |
| 9–13 m (C): fs, Qs | 46 kPa, 350 kN | σ′v 108 |
| 13–18 m (S): fs, Qs | 60 kPa, 565 kN | σ′v 151 |
- ✓ Rd,g ≥ N* — 2,581 vs 2200
Method, formulas and assumptions
- Clay: fs = α·su, α = 0.5ψ^−0.5 (ψ ≤ 1) or 0.5ψ^−0.25 (ψ > 1), ψ = su/σ′v (API RP2A); base 9su
- Sand: fs = ks·N̄ ≤ limit (Meyerhof 1976 suggests ks ≈ 2 for driven, ≈ 1 for bored); qb = kb·N ≤ limit
- Rd,g = φg·Rd,ug; φg must come from the AS 2159 risk rating and testing regime: the default is only an example
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.