Foundations · Pile capacity
Pile capacity and settlement from CPT (LCPC method) calculator
Pile designed directly from a cone penetration test, by the direct CPT method. The equivalent base resistance qca is the mean qc within 1.5D above and below the toe, clipped to 0.7–1.3 times that mean; qb = kc·qca. Shaft friction in each reading is qc/α limited by the LCPC maximum for clay/silt or sand/gravel and bored or driven piles. The design capacity uses φg, and the settlement at the working load uses the Randolph–Wroth stiffness with soil modulus from qc.
Standard: Bustamante & Gianeselli (1982) LCPC method · AS 2159-2009 φg · Randolph & Wroth (1978) head stiffness with E = αE·qc
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 |
|---|---|---|
| CPT: depth (m), qc (MPa), soil (1 = clay/silt, 2 = sand/gravel) | 0.5, 0.85, 1 1.0, 0.90, 1 1.5, 0.95, 1 2.0, 1.00, 1 2.5, 1.05, 1 3.0, 1.10, 1 3.5, 1.15, 1 4.0, 1.60, 1 4.5, 1.68, 1 5.0, 1.75, 1 5.5, 1.83, 1 6.0, 1.90, 1 6.5, 1.98, 1 7.0, 2.05, 1 7.5, 2.13, 1 8.0, 2.20, 1 8.5, 2.27, 1 9.0, 2.35, 1 9.5, 2.42, 1 10.0, 2.50, 1 10.5, 2.58, 1 11.0, 2.65, 1 11.5, 2.73, 1 12.0, 9.00, 2 12.5, 9.40, 2 13.0, 9.80, 2 13.5, 10.20, 2 14.0, 10.60, 2 14.5, 11.00, 2 15.0, 11.40, 2 15.5, 11.80, 2 16.0, 12.20, 2 16.5, 12.60, 2 17.0, 13.00, 2 17.5, 13.40, 2 18.0, 13.80, 2 18.5, 14.20, 2 19.0, 14.60, 2 19.5, 15.00, 2 20.0, 15.40, 2 | |
| Pile type | Bored / CFA (LCPC category I) | |
| Diameter | 0.6 | m |
| Length (toe depth) | 16 | m |
| Geotechnical reduction φg | 0.5 | |
| Design load N* | 800 | kN |
| Working (serviceability) load | 600 | kN |
| Pile modulus | 30000 | MPa |
| Soil modulus factor E = αE·qc | 3 | |
| Soil Poisson's ratio | 0.3 | |
| Allowable settlement | 15 | mm |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Mean qc within ±1.5D of the toe | 12.20 | MPa |
| Equivalent qca (clipped 0.7–1.3) | 12.20 | MPa |
| Base factor kc | 0.15 | |
| Base resistance qb / Rb | 1,830 kPa / 517 kN | |
| Shaft resistance Rs | 1,252 | kN |
| Ultimate capacity Rug | 1,769 | kN |
| Design capacity φg·Rug | 885 | kN |
| Average shaft modulus / base modulus | 12.8 / 36.6 | MPa |
| Head stiffness (Randolph–Wroth) | 121 | MN/m |
| Settlement at the working load | 4.9 | mm |
- ✓ N* ≤ φg·Rug — 90 %
- ✓ Settlement ≤ allowable — 4.9 mm
- ✓ CPT extends ≥ 1.5D below the toe
Method, formulas and assumptions
- LCPC: qca = mean of qc within a = 1.5D above and below the toe after discarding values outside 0.7–1.3 of the raw mean; qb = kc·qca with kc = 0.375 (clay/silt) or 0.15 (sand/gravel) for this pile type.
- Shaft friction per reading fs = qc/α ≤ fmax with α and fmax from simplified LCPC categories (bored); integrate fs·πD over the shaft.
- Settlement: Randolph & Wroth with G = E/2(1 + ν), E = αE·qc averaged over the shaft (αE ≈ 2–4 sand, 3–6 clay).
- Values are indicative; calibrate α and kc with static load tests (AS 2159 Sec 8).
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.