Why councils and certifiers ask for one
Conditions usually come from one of three places: the site is steep or sits in an area the council has mapped for landslip or geotechnical risk; the proposal involves a basement, a deep excavation or a retaining wall that could affect neighbours; or the ground itself is known to be difficult, such as fill, soft alluvium or shallow rock. The report gives the council and the certifier confidence that the design accounts for the ground, and gives your structural engineer the numbers they need.
The investigation
The fieldwork is scoped to the proposal, which is why it is quoted from the address and the condition rather than priced as a fixed fee.
- Boreholes or test pits at the building footprint, taken to the depth the design needs: below a basement floor, below a retaining wall's toe, or to rock
- Logging of every hole to AS 1726, the standard for geotechnical site investigations
- In-situ testing where it helps, such as dynamic cone penetrometer tests for strength with depth
- Groundwater observations, and where the design depends on it, a standpipe left in a borehole
- Laboratory testing of samples for strength, moisture, plasticity and shrink-swell behaviour as the design requires
What the report contains
A geotechnical report for a residential or small commercial proposal typically runs through the following, with the borehole logs attached.
- The site and the proposal: address, what is being built, who asked for the report and which condition it answers
- Regional and site geology, and what the investigation found: the soil and rock profile, fill, groundwater
- Allowable bearing pressure and recommended founding level for footings, and for piers or piles where the ground needs them
- The AS 2870 site class where the proposal is residential and the footing designer needs it
- Excavation: how the ground is expected to excavate, batter slopes for temporary cuts, and where shoring or support is needed
- Retaining walls: design parameters such as soil unit weight, friction angle and earth pressure coefficients, and drainage requirements behind the wall
- Slope stability commentary where the site is sloping or mapped for landslip risk
- Drainage, and any risks to neighbouring structures from excavation or dewatering
- Limitations: what the boreholes can and cannot say about the ground between them, and when to call for an inspection during construction
What to send with the enquiry
The wording of the condition or the certifier's request is the most useful thing, because it tells us what the report has to answer. A site plan or survey with levels, the architectural drawings if they exist, and any earlier soil report for the block all help the quote be accurate. You can attach these to the enquiry form. With them we can usually quote the same day.
What it is not
A geotechnical report describes the ground and gives the design parameters. It does not design the footing, the retaining wall or the shoring: that is your structural engineer's job, using the report. It also does not cover contamination, which is a separate assessment under a different set of rules, or detailed slope stability analysis for large or high-risk slopes, which Australian Ground Sciences handles as a larger project.
Questions
Last checked 9 September 2026. Written by the engineers at Australian Ground Sciences, who prepare and sign the reports.