Geotechnical report vs desktop assessment: what's the difference?
Geotechnical professionals use these two terms to describe different scopes of work — and understanding the difference helps you know what to commission and when. A geotechnical report is a broad term covering any written output from ground investigation; a desktop assessment is one specific type, defined by its reliance on existing data rather than physical investigation.
The core distinction
A desktop assessment (also called a desktop study or preliminary geotechnical assessment) is carried out entirely from existing records: geological maps, soil surveys, historical borehole data, topographic information, and remote sensing. A geotechnical engineer reviews these sources and produces a written assessment of probable ground conditions. No drilling. No laboratory testing. No site visit is required.
A geotechnical site investigation involves physical work on the ground: drilling boreholes or excavating test pits, collecting soil or rock samples, conducting in-situ testing (SPT, CPT, vane shear), and sending samples to a laboratory for characterisation. The resulting report is based on tested, site-specific data.
A full geotechnical report typically refers to a site investigation report — though the term is loose and the scope depends on the project.
What each one tells you
| Desktop assessment | Site investigation | |
|---|---|---|
| Data source | Existing records | Physical testing |
| Turnaround | Hours to days | Weeks |
| Cost | Low | Moderate to high |
| Site-specific data | No | Yes |
| AS 2870 classification | Often possible | Always possible |
| Class P resolution | No | Yes |
| Suitable for complex sites | Limited | Yes |
| Suitable for early-stage | Yes | Often premature |
When to use each
Use a desktop assessment when:
- You're in pre-purchase, pre-design, or feasibility stage
- Ground conditions in the area are reasonably well documented
- You need to understand likely soil type, reactivity, and groundwater depth quickly and cheaply
- You're screening multiple lots before committing to physical investigation
- An indicative AS 2870 site classification is sufficient for your current purpose
Proceed to site investigation when:
- Ground conditions are complex, unknown, or suspected to be problematic
- The desktop assessment returns a Class P classification, which requires physical characterisation
- A structural engineer or building certifier requires tested, site-specific data
- The proposed structure is sensitive (large footprint, basement, sloped site, multi-storey)
- You're about to commit to footing design on a significant project
The sequencing logic
These two approaches aren't alternatives — they're stages. The right workflow for most development projects is:
- Desktop assessment first — establish probable ground conditions quickly and cheaply; identify whether the site is likely to be standard or problematic
- Site investigation if warranted — directed by the desktop findings; drill where you most need to know, and target the right tests
Commissioning a full site investigation on every lot before purchase, without a desktop filter, is expensive and often premature. Relying only on a desktop assessment for a complex or high-consequence project is a false economy.
What LayeredGeo provides
LayeredGeo delivers automated geotechnical desktop assessments for Queensland and NSW properties — geology, soils, AS 2870 classification, groundwater, topography, and environmental overlays compiled into a PDF in minutes.
It's designed for the first stage of that workflow: rapid, data-driven ground intelligence to support pre-purchase decisions, development feasibility, and early project planning.
View a sample report or get started.
LayeredGeo is an automated geotechnical desktop reporting platform serving the residential development sector in Queensland and New South Wales.