Geotechnical report vs desktop assessment: 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:

1. Desktop assessment first: establish probable ground conditions quickly and cheaply; identify whether the site is likely to be standard or problematic
2. 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.

See a sample report or generate a desktop report for the address.

---

LayeredGeo is an automated geotechnical desktop reporting platform serving the residential development sector in Queensland, New South Wales and Victoria.

About this article. Published by LayeredGeo. It is general information about how property and ground conditions are assessed in Australia, not engineering, planning, legal or financial advice, and it is not specific to any property. Check anything that matters against the source dataset or a suitably qualified professional before you rely on it. If you spot something wrong, tell us at hello@layeredgeo.com.au and we will fix it.

← All articles