Site investigation · Laboratory: soil classification
Liquid limit: cone penetrometer calculator
Linear fit of moisture content against cone penetration; the liquid limit is w at 20 mm penetration.
Standard: AS 1289.3.9.1 · BS 1377-2
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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 |
|---|---|---|
| Points: penetration (mm), moisture (%) | 15.2, 38.1 17.9, 40.6 21.4, 43.2 24.8, 46.0 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Slope dw/dp | 0.813 | %/mm |
| Intercept | 25.86 | % |
| Liquid limit (w at 20 mm) | 42.12 | % |
| Fit R² | 0.998 |
- ✓ Readings span 15–25 mm
- ✓ Good linear fit (R² ≥ 0.95)
Method, formulas and assumptions
- Slope dw/dp = SLOPE([t.w],[t.p]) = 0.81262 %/mm
- Intercept = INTERCEPT([t.w],[t.p]) = 25.865 %
- Liquid limit (w at 20 mm) = 25.865+0.81262*20 = 42.117 %
- Fit R² = RSQ([t.w],[t.p]) = 0.99848
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.