AS 3798-2007: earthworks for commercial and residential developments

TL;DR

AS 3798:2007 (incorporating Amendment 1) is the Australian Standard for site earthworks on commercial and residential builds. It sets the framework for placing, compacting, and testing fill so a building can sit on it without ongoing settlement. The two builder-facing items are the supervision level (Level 1 means a Geotechnical Inspection and Testing Authority on site through the works; Level 2 means periodic visits) and the compliance report (the GITA’s certificate that the fill meets specification). AS 2870 calls AS 3798 up whenever a residential slab sits over engineered fill: no AS 3798 compliance report, no controlled-fill status, and the site classification drops to Class P with a full engineered slab.

In plain English

AS 3798 is the rulebook for the site preparation work that happens after the surveyor pegs the corners and before the concretor pours the slab. It governs how the natural ground is assessed, how spoil is excavated and reused or removed, how fill is brought in and placed, and how the finished platform is tested. Without an AS 3798-compliant process, fill placed under a slab is treated by AS 2870 as uncontrolled and forces the site into Class P, where every slab design becomes a custom engineering job.

The standard does three things:

Defines the supervision levels (Level 1 and Level 2) that determine how closely a geotechnical professional watches the works.
Sets the material and compaction specifications for cohesive and granular fill: target density, allowable moisture range, lift thickness, test frequency.
Defines the certification chain that ends with the GITA’s compliance report.

It does not classify the site (that is AS 2870), design the slab (AS 2870 or engineer), or design the pavement (Austroads or council standards).

What it requires

Supervision levels

Level	What it looks like	When it applies
Level 1	A GITA is engaged before work starts, attends continuously, inspects each lift before the next is placed, takes density and moisture tests in real time, and signs the compliance report.	Engineered fill under slabs, footings, or load-bearing structure.
Level 2	A Geotechnical Testing Authority (GTA) attends periodically on call from the builder, takes spot tests, and reports results. No overall validation of methodology.	Lightly-loaded fill, landscaped or paved areas where settlement is non-structural.

The distinction matters because a Level 2 report does not give the certifier what AS 2870 wants. If the engineer specs controlled fill under the slab, Level 1 is the only path.

Materials and compaction

The standard prescribes what can be used as engineered fill (clean granular material in most cases; cohesive material under controlled moisture is allowed but harder), the maximum lift thickness before compaction (typically 200 to 300 mm depending on equipment), and the compaction target. Targets are typically expressed as percentage of standard maximum dry density (MMDD), with 95 to 98 per cent the residential range. Field density is verified by sand replacement or nuclear density gauge testing, with frequencies set by the specification.

Compliance report

The GITA issues a single compliance report at the completion of earthworks. The report covers material conformance, layer placement, compaction results, and any non-conformances and how they were resolved. The builder hands the report to the certifier as evidence the fill is fit for the design loads.

What it doesn’t cover

Site classification (Class A, S, M, H1, H2, E, P): that is AS 2870 using soil reports.
Slab design: AS 2870 (residential) or AS 3600 (concrete structures).
Pavement design: Austroads or local council pavement design standards.
Retaining walls: AS 4678, plus geotechnical design.
Demolition: separate scope under AS 2601.
Pre-existing fill under brownfield sites: the standard governs new placement; investigating and re-classifying historic fill is a separate forensic exercise.

Practical implications

Lock in the supervision level before quoting. Level 1 supervision adds material cost to the earthworks line: typically a continuous engineer presence plus testing for the duration. Knowing whether the engineer has specified Level 1 changes the earthworks quote.

Get the GITA engaged before the first bucket moves. AS 3798 explicitly relies on inspection of the existing ground before fill is placed. A GITA called to a site where the fill is already down has nothing to inspect; the works have to be remediated or re-stripped.

Moisture is non-negotiable. Compaction tests can read at-target but the fill was placed too wet and will consolidate after the slab is poured. The GITA controls moisture-content windows (typically optimum minus 2 to optimum plus 2 per cent) and stops work outside that range. Build the moisture-control budget into the earthworks programme: cover stockpiles in wet weather, water cohesive fills in dry.

The compliance report is the certifier’s gate. A complete report on the build pack means the slab pour proceeds. Missing report or unresolved non-conformances delay the slab and every downstream trade.

Pre-existing fill is the silent killer. A site that historically had fill placed without AS 3798 supervision (former orchard pad, demolished structure pad, infill block) is automatically uncontrolled. The geotech will either require it be stripped and re-placed under AS 3798 or accept the Class P slab penalty.

Source link

The standard is published by Standards Australia and available through Standards Australia / SAI Global. Excerpts and guides from major geotechnical consultancies (Douglas Partners, Soil Surveys, Ideal Geotech, GSG Labs) are referenced below for plain-English overviews; the standard itself is the authoritative source for compliance.

References

AS 3798:2007 Incorporating Amendment 1, Standards Australia (verified 2026-05-14).
Douglas Partners Level 1 testing and risk management overview (verified 2026-05-14).
GSG Laboratories Level 1 vs Level 2 testing guide (verified 2026-05-14).
AS 2870:2011, Residential slabs and footings (referenced for the controlled-fill consequence chain, verified 2026-05-14 via Standards Australia).