Test NotesCBR Correlation Chart & Site Notes
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CBR Correlation Chart
| Location | Weighted Blows/50 mm | mm/blow | *Inferred CBR |
|---|---|---|---|
| No locations available. | |||
Weighted CBR by Location (first 3 intervals to 150 mm)
Scala to CBR Conversion Method
Scala blows are accumulated with depth and converted to a penetration rate (mm/blow). Inferred CBR is then estimated from the Western Bay of Plenty District Council (WBOPDC) Scala Penetrometer CBR Conversion Chart (APP.2) using a log-log correlation fit to the chart lines.
Implemented correlation (chart-fit):
log10(CBR) = 2.657 - 1.292 * log10(penetration (mm/blow)) (equivalently, CBR = 10^2.657 * (mm/blow)^(-1.292))
- This is an empirical inferred-CBR correlation (not a direct laboratory CBR test).
- DCP/Scala-to-CBR relationships vary by soil type, moisture condition, and local practice; local calibration and/or confirmation with in-situ or laboratory CBR testing is recommended for design acceptance.
- Scala results are useful to identify weak layers and subgrade variability with depth.
- Design subgrade assessment: NZ guidance recommends using a weighted average of blows/50 mm over the first three 50 mm intervals (0.7, 0.2, 0.1) before converting to mm/blow and inferred CBR.