Geotechnical investigations should be in accordance with the following Australian Standards;
- AS2870-1996: “Residential Slabs and Footings – Construction”
- AS1726-1993: “Geotechnical site investigations”
The classification of the site is based on the expected movement of the foundation soils – generally related to the capacity of the soil to shrink or swell.
Your site should be in one of the following classifications:
Slightly reactive clay sites. Only slight ground movement from moisture changes expected.
Moderately reactive Clay or Silt sites which can experience moderate ground movement from moisture changes (See this link: Building on Clay).
Highly reactive clay sites. Can experience high ground movement from moisture changes.
Extremely reactive sites. Can experience extreme ground movement from moisture changes.
A problem site. This can includes soft soils, such as soft clay or silt, varying depths of Fill (see this link: Fill), loose sands, landslips, mine subsistance, collapsing soils, soils subject to erosion, reactive sites subject to abnormal moisture conditions, or sites which cannot be classified otherwise.
Soil types M, H, and E may also have an added classification of ‘D’. This indicates deep seasonal moisture variation which can mean significant expansion and contraction.
For example, from a dry to a saturated state
- Class M-D may move up to 40mm,
- Class H-D 40mm to 70mm
- Class E-D can move more than 70mm, (up to 250mm has been found in some cases)
If you are looking at a Project Builders its worth being aware that their standard price will be based on either an S or M class foundation. Usually you will be lucky if the foundation is in this range………so you could be up for additional costs.
See the following link to understand why a classification from the developer may be better than the one from the builder: Different Soil Classification Results
Lots more information in the anewhouse Guide to Buying a Block for only $4
For more posts related to land see Blocks