Foundations · Pile capacity
Rock-socketed pile: capacity and settlement (Rowe & Armitage) calculator
Bored pile socketed into rock below a soil overburden. Socket side resistance f = k√qu (Rowe & Armitage: k = 0.45 for smooth sockets, 0.6 for rough), base resistance Nb·qu, design capacity with φg (AS 2159), elastic head settlement from Randolph & Wroth's solution using the rock-mass modulus plus pile shortening, and the share of load reaching the base.
Standard: Rowe & Armitage (1987) · Pells (1999) · Randolph & Wroth (1978) elastic settlement · AS 2159-2009
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 |
|---|---|---|
| Socket diameter | 0.9 | m |
| Socket length | 3 | m |
| Overburden (pile length above rock) | 6 | m |
| Rock UCS qu | 10 | MPa |
| Socket roughness | Smooth (R1–R3): f = 0.45√qu | |
| Base factor qb = Nb·qu | 2.5 | |
| Rock-mass modulus Er | 1500 | MPa |
| Pile modulus Ep | 32 | GPa |
| Rock Poisson's ratio | 0.25 | |
| Geotechnical reduction φg | 0.55 | |
| Design action N* | 6000 | kN |
| Service load | 4000 | kN |
| Allowable settlement | 15 | mm |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Socket side shear f | 1,423 | kPa |
| Side resistance Rs | 12,071 | kN |
| Base resistance Rb | 15,904 | kN |
| Design capacity φg(Rs + Rb) | 15,386 | kN |
| Socket head stiffness | 4,372 | MN/m |
| Elastic shortening through overburden | 1.18 | mm |
| Settlement at service load | 2.09 | mm |
| Share of load at the base (elastic) | 28.0 | % |
- ✓ N* ≤ φg·Rug — 6,000 vs 15,386 kN
- ✓ Settlement ≤ allowable — 2.09 mm
- ✓ Socket length ≥ 1.5D
Method, formulas and assumptions
- Rowe & Armitage (1987): f = 0.45√qu (MPa) for clean smooth sockets, 0.6√qu for rough (R4); base qb taken as Nb·qu (2.5 suggested for design with settlement control).
- Settlement: Randolph & Wroth with G = Er/2(1 + ν) over the socket, plus P·Lo/(A·Ep) through the overburden (no shaft resistance assumed in soil).
- φg from the AS 2159 risk assessment (average risk with no testing ≈ 0.5–0.6).
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.