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In Australia, geotechnical site classification follows key standards: 'AS 2870: Residential Slabs and Footings' and 'AS 1726-2017: Geotechnical Site Investigations'. While AS 1726 governs site investigations, AS 2870 outlines specific guidelines for soil classification and footing design. Failure to adhere to these standards can lead to structural damage, including cracking and other long-term issues
Before you begin planning your build or designing your foundations, obtaining a site classification is a crucial first step. It helps you understand the soil conditions of your property, ensuring you select the right foundation to suit its unique environment.
As the subsurface soil conditions and their soil properties can be varied widely, a geotechnical site classification report ensures that footing and foundation designs for buildings are based on tested subsoil strength parameters specific to the site. The site classification will be assigned to each lot according to geotechnical investigation and analysis.
| # | SITE CLASSIFICATION | DESCRIPTION |
|---|---|---|
| 1 | A | Mostly sand and rock: Sites that have little to no movement |
| 2 | S, Ys=0 to 20mm | Slightly Reactive Clay: Sites that may experience slight ground movements |
| 3 | M, Ys = 20 to 40 mm | Moderately Reactive Clay or Silt: Sites that may experience moderate ground movement |
| 4 | H1, Ys = 40 to 60 mm | Highly Reactive Clay: Sites that may experience high amounts of ground movement |
| 5 | H2, Ys = 60 to 75mm | Very Highly Reactive Clay: Sites that may experience very high amounts of ground movement |
| 6 | E, Ys = greater than 75mm | Extremely Reactive Clay: Sites that may experience extreme amounts of ground movement |
| 7 | P | Problem sites: Sites that may be subject to abnormal moisture conditions, like special soil, risk of erosion or landslides |
Previously, some footing designs were based on engineers' assumptions made from desktop studies, which led to either over-designed foundations, resulting in unnecessary costs for clients, or under-designed foundations, which pose significant future risks such as excessive settlement, structural failure, and wall/ceiling cracking.
Wall cracking due to excessive footing settlement on soft soil ground
Ceiling cracking as a result of ground movement
'Building Commission NSW encourages all design and building practitioners to seek and rely on a detailed geotechnical report and not assume soil parameters according to preliminary reports. The reminder comes after a recent audit found a final geotechnical report was missing before the construction of a multi-storey building.' - The Building Commision NSW News reported at 6th of Nov 2024.
As part of ongoing efforts to improve building safety, NSW Fair Trading and the Building Commission NSW have clarified that for Class 1a Dwellings (such as houses, duplex, town houses and granny flats), Structural Engineering Plans must reference a soil classification report, this is where we can help, please contact us to discuss with us about your project.
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