Site Classification – 2.1.2 – Site Classification based on soil reactivity
All sites are required to be classified. The footing system by the engineer has to be suitable for each and individual site and the only method of achieving this is to assess the site and it to classify it.
The main soil types are sand and clay, with silt as an intermediate type.
The various types of soil are distinguished in an engineering assessment by the size of the particles that constitute the soil such as follows;
- sand – which comprises material down to 0.075 mm;
- silt – which includes the range 0.075 mm to 0.002 mm; and
- clay – which consists of very fine particles smaller than 0.002 mm.
The terms sand, silt and clay have been broadened in this Australian Standard for the purpose of general construction. When soils contain mixed types, the finer particles usually control behaviour in the ground. For example, clayey sand behaves more like a clay than a sand.
For the purpose of this article, sand is defined as soil with less than 15% clay and silt fines, and silt is redefined as a fine-grained but non-plastic and non-cohesive soil. It is important to realize these simplified classifications are different from conventional geotechnical engineering classifications.