Understanding the site you build on.

According to AS2870 (2011) Residential Slabs & Footings, “Site Classification is based on the expected ground surface movement and the depths to which this movement extends”. This Site Classification gives an indication of the expected amount of movement of the soils across the intended building site, which indicates the reactivity (movement) of the soils in that particular location.

 Foundations are the ground that supports the footing system. Footings are the construction that transfers the load from the building to the foundation.

The construction of a building’s footing system will depend on the site classification so that it is able to combat the level of expected movement (shrink or swell) in the foundation earth.

Site Soil Classifications are as follows;

Class A (Movement: 0mm)

Includes many sand, gravel & rock sites with no clays. These sites have no expected movement and as a result zero moisture variation.

Class S (Movement: 0 - 20mm )

Slightly reactive sites which exhibit only small movements with moisture variation.

Class M (Movement: 20 - 40mm )

Moderately reactive sites exhibit moderate amounts of movement with moisture variation. These sites commonly include red/brown silty soils, some sandy clays, and loamy soils.

Class H1 (Movement: 40 - 60mm )

Highly reactive sites exhibit high amounts of movement with moisture variation.

Class H2 (Movement: 60 - 75mm )

Highly reactive sites exhibit high amounts of movement with moisture variation.

Class E (Movement: >75mm )

Extremely reactive sites which exhibit greater than 75mm of surface movement. Typically, these sites include deep reactive clays, such as black and dark brown soils. These sites typically demand quite expensive footing systems.

 Class P (Problem Site)

The reasons for a P classification include:

 Growth &/or Removal of Trees will cause Abnormal moisture conditions in the subsurface soils;

 Unusually high moisture conditions caused by water flow, ponds, dams etc;

 Sites with Loose-fill which can be either “controlled” or “uncontrolled”. The P Classification depends upon the depth and type of fill;

 Sites with poor bearing capacity, soft soils, or soils which are prone to collapse;

 Sites prone to mine subsidence, landslip, piping or coastal erosion;

 Sites that for one reason or another cannot be classified as normal sites

In short, a rule of thumb is the more reactive the site soil, the more extensive the engineering requirements from a base stage perspective.