Site investigation · In-situ testing
DCP to CBR calculator
Penetration per blow by layer and estimated in-situ CBR, plotted with depth.
Standard: AS 1289.6.3.2 · CBR = 292/DN^1.12 (Webster et al. 1992)
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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 |
|---|---|---|
| Cumulative blows, depth (mm) | 0, 0 2, 90 4, 170 6, 235 8, 290 10, 335 14, 410 18, 470 24, 540 | |
| Design subgrade CBR | 5 | % |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| 0–90 mm: DN | 45.0 mm/blow | CBR ≈ 4.1 % |
| 90–170 mm: DN | 40.0 mm/blow | CBR ≈ 4.7 % |
| 170–235 mm: DN | 32.5 mm/blow | CBR ≈ 5.9 % |
| 235–290 mm: DN | 27.5 mm/blow | CBR ≈ 7.1 % |
| 290–335 mm: DN | 22.5 mm/blow | CBR ≈ 8.9 % |
| 335–410 mm: DN | 18.8 mm/blow | CBR ≈ 11.0 % |
| 410–470 mm: DN | 15.0 mm/blow | CBR ≈ 14.1 % |
| 470–540 mm: DN | 11.7 mm/blow | CBR ≈ 18.6 % |
- ✗ All layers ≥ design CBR
Method, formulas and assumptions
- DN = Δdepth / Δblows
- CBR ≈ 292 / DN^1.12 (one widely used correlation; others exist, so calibrate locally)
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.