Site investigation · Laboratory: soil classification
Emerson class number (dispersion) calculator
Decision tree for the Emerson class (1–8) from observed slaking, dispersion and swelling of soil aggregates.
Standard: AS 1289.3.8.1
Open the live calculator → All site investigation calculators
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 |
|---|---|---|
| Air-dry aggregate slakes? | Yes | |
| Air-dry aggregate disperses (complete or partial)? | None | |
| Remoulded soil disperses? | Yes | |
| Calcite/gypsum present? | No | |
| 1:5 suspension remains dispersed? | No | |
| Swells (no slaking)? | No |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Emerson class | 3.00 | |
| Dispersion risk | moderate |
- ✗ Not dispersive (class ≥ 4)
Method, formulas and assumptions
- Emerson class = IF(1=0,IF(0=1,7,8),IF(0=2,1,IF(0=1,2,IF(1=1,3,IF(0=1,4,IF(0=1,5,6)))))) = 3
- Dispersion risk = IF(3<=2,"high",IF(3=3,"moderate","low")) = moderate
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.