Soil testing and site classification is conducted to identify a variety of issues which must be considered when planning to build on a specific site. Reduced bearing capacity is a problem that must be recognised and addressed. This is a common issue in Brisbane where many suburbs are built on natural clay deposits.
Where a site is to be built on clays, the same moisture susceptibility that caused shrinking and swelling of clays also reduces their capacity to bear weight. As these clays absorb water, they become soft, much like playdough. When a load such as a footing or foundation is applied to these soft, low bearing capacity soils, the foundations move and affect the stability of the building. Damage may occur as a result.
It is not uncommon to see fill brought to a site that contains a significant amount of clay. Often this material is placed over what are otherwise stable local soils. It is possible in this situation to “import” problems to your site when utilising uncontrolled fill. This problem can be avoided by utilising controlled fill for which engineering properties are known.