Describing soils
Word order, consistency, density index, moisture and constituent proportions.
Before you use this section
The conventions below follow general Australian practice for soil and rock description, broadly after AS 1726. Your own QA manual, and any project specification, take precedence. Where the two differ, follow your procedures — and if you are unsure which applies, ask the reviewing engineer before you log, not after.
A soil description is read by people who will never see the sample. Its job is to convey the material precisely enough that someone can make a decision from it years later.
The word order
Descriptions follow a fixed order. Keeping to it is what makes logs comparable across holes, jobs and staff:
- Consistency or density index
- Moisture condition
- Colour
- Secondary and minor constituents
- PRIMARY SOIL NAME — in capitals
- Plasticity or particle characteristics
- Structure and additional observations
- Origin, where known
For example:
very stiff, moist, grey with light orange/red mottling, medium to high plasticity CLAY, trace ironstone gravel
The most common logging error is putting these out of order — most often leading with colour, which buries the engineering properties behind an aesthetic one.
Consistency — cohesive soils
Assessed by hand or by undrained shear strength.
| Term | Abbreviation | Guide |
|---|---|---|
| Very soft | VS | Exudes between fingers when squeezed |
| Soft | S | Easily moulded |
| Firm | F | Moulded with strong finger pressure |
| Stiff | St | Cannot be moulded; indented by thumb |
| Very stiff | VSt | Indented by thumbnail |
| Hard | H | Difficult to indent |
Density index — granular soils
Assessed from SPT N values or penetration resistance, not by hand.
| Term | Abbreviation |
|---|---|
| Very loose | VL |
| Loose | L |
| Medium dense | MD |
| Dense | D |
| Very dense | VD |
Do not report a consistency term for a sand or a density term for a clay. It signals the logger did not know which material they had.
Moisture condition
| Term | Meaning |
|---|---|
| Dry | No moisture apparent |
| Moist | Damp, no free water |
| Wet | Free water present |
For cohesive soils, moisture is often better expressed relative to the plastic limit — below PL, near PL or above PL — because that relates directly to behaviour.
Secondary constituents
Proportion words matter and are not interchangeable:
- trace — a small amount, barely affecting behaviour
- with — present in enough quantity to influence behaviour
- -y suffix, as in sandy or silty — a significant proportion
CLAY with sand and sandy CLAY describe different materials.
Entering it in GeoCRM
The Lithology tab splits this into the short attribute fields — material, colour, moisture, consistency — and a full description field. The attributes drive the graphic log and classification symbol; the full description prints in the material description column. Fill in both. See Logging lithology.