BCGBC4010A Apply structural principles to residential low-rise constructions

Footing system

Foundation soils

Soil types
Rock sites
Building houses on solid rock foundations is the best structural solution. Rock is the most stable foundation. However, these sites cause cost difficulties with excavations for footings, water pipes, sewer pipes, underground power, gas and stormwater drainage. So, generally, rock sites are not viewed favourably.
Sand sites
Housing sites located on sand are the best sites. Sand is capable of supporting up to four-storey houses. It is generally easy to excavate with a hand shovel.
Clay sites
Clay sites are among the most common in Australia. They are the main type of site around our capital cities. Clay surface movements range from relatively small to extremely large. 
Clay soil is measured by its ability to expand or contract with the addition or subtraction of water. The measure is referred to as its 'reactivity'. These reactive soils change according to seasonal changes in the moisture content. 
Swelling soils will lift footings and their buildings and can cause significant structural damage. Shrinking during dry periods causes buildings to sink and crack.
Problem sites
Poor supporting soils include soft clays, wet sand, dump sites containing uncontrolled fill or rubbish, loose soil and unknown or unclassifiable material. These sites are unpredictable and cause the biggest problem for footing designers. Such sites require an engineer to design appropriate foundations.

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