Soil report (geotech)
What a soil report covers, the site classification categories (A, S, M, H1, H2, E, P) under AS 2870, and how it drives slab and footing design.
Ask Chalkline about this →A soil report (often called a geotech report) is a pre-construction site investigation covering ground conditions: soil type, layering, reactive movement, water table, and any contamination or fill. For residential work, the report classifies the site under AS 2870 so the structural engineer can spec a footing and slab system that’s appropriate for the ground.
Site classifications under AS 2870
| Class | Behaviour | Typical |
|---|---|---|
| A | Stable, non-reactive | Sand or rock |
| S | Slightly reactive | Light clay |
| M | Moderately reactive | Most metro clay sites |
| H1, H2 | Highly reactive | Heavy clays, deep movement |
| E | Extremely reactive | Severe shrink-swell |
| P | Problem site | Fill, soft soils, deep mine workings, mine subsidence, soft / loose sands, abnormal moisture, abnormal ground movement |
Class P is the catch-all for anything outside the standard classes; it always requires custom engineering, not a deemed-to-satisfy slab.
What’s in a typical report
- Borehole or test pit logs to a depth specified for the site class
- Soil descriptions per AS 1726 (geotechnical site investigations)
- Site classification (A through P)
- Recommendations for footing system and slab type
- Notes on drainage, fill, trees within the influence zone (TPZ)
Why it matters at quote and DA stage
The class drives the slab cost (a Class M slab is meaningfully cheaper than an H2 raft slab). Quoting a slab without a soil report is a guess. Most certifiers and lenders require the report before issuing a Construction Certificate.
Also known as: Geotech, geotechnical investigation, site classification report.
Category: Site.