Adelaide soil types and cracking foundations

A pile of soil in the back of a white truck

What has dirt got to do with my cracked foundation?

It is important to know and understand how different Adelaide soil types can crack a foundation and affect the need for underpinning in Adelaide.

Soil type plays a significant role in determining the need for underpinning and there are several reasons why:

  • Compression strength: Certain soil types, such as clay, have low compression strength and can settle over time, causing the foundation to sink and potentially leading to structural damage.
  • Moisture content: Soil with high moisture content, such as peat or organic soils, can be susceptible to compaction and settlement.
  • Erosion: Soils in areas prone to erosion, such as those near bodies of water, can cause the foundation to shift and become unstable.
  • Subsidence: Soils in areas with high water tables or prone to subsidence, such as areas with expansive clay soils, can cause the foundation to sink.

How can you tell the difference between the different types of soil?

In Australia, the Soil Classification System is used to group soils into four main classes: Sands, Clays, Loams, and Organic Soils. Within each class, soils are further divided into subclasses based on properties such as texture, structure, and nutrient content.

Soil classification is important because it provides information about soil fertility, water-holding capacity, drainage, and erosion potential. This information is critical for making informed decisions about land use and management, and helps to ensure the long-term productivity and sustainability of the land.

According to the Australian Standard AS 2870-2011, a building code that provides guidelines and standards for the design and construction of residential buildings in Australia, there are seven different soil classes found in Australia, otherwise known as Soil Class Foundation.

What is the meaning of Soil Class Foundation?

The soil class foundation refers to the grouping and classification of soils based on their physical and chemical characteristics. This system of classification helps to determine the suitability of soil for different types of land use, such as agriculture, forestry, and residential development. The common Adelaide soil types can be classified as follows:

A – Sand and rock sites with little or no ground movement from moisture changes

S – Slightly reactive clay sites with only slight ground movement from moisture changes

M – Moderately reactive clay or silt sites which can experience moderate ground movement from moisture changes

H1 – A high rate of ground movement (40–60 mm of surface movement)

H2 – A very high rate of ground movement (60–75 mm of surface movement)

E – Extremely reactive clay sites which can experience extreme ground movement from moisture changes

P – Soft soils, such as soft clay or silt or loose sands; landslip; mine subsidence; collapsing soils; soils subject to erosion, and other unclassifiable or problem sites

A man on a small digger dumping soil into a truck

Why do I need my soil tested if underpinning is needed?

The exact composition of the soil of your land will depend on its location and geology. Getting soil tested prior to construction or extensive renovation of a home or if there are signs of major structural damage, is important for many reasons, including:

  • Foundation stability: The soil type and its physical properties, such as compaction and moisture content, can greatly impact the stability of the foundation of a building. If the soil is not suitable, additional measures may need to be taken to ensure the foundation is stable, such as deeper pilings in the footing.
  • Soil settlement: Certain types of soil, such as clay, can expand and contract over time, causing settling or shifting that can lead to structural damage to the building. Soil testing can help identify potential soil settlement issues, allowing for the proper design and construction of the foundation.
  • Groundwater: Groundwater levels can impact the stability of the building and also affect the suitability of the site for septic systems or underground utilities. Soil testing can help determine the level of groundwater in the area and its impact on the building.
  • Soil contamination: Soil contamination from pollutants such as heavy metals, petroleum products, or chemicals can pose a risk to human health and the environment. Soil testing can help identify the presence of contaminants and the extent of the contamination, allowing for proper remediation measures to be taken prior to construction.


What are the factors that determine underpinning?

It is important to note that while Adelaide soil types can impact the need for underpinning, it is just one of the many factors. These other factors include things like the age of the building, failed plumbing, nearby excavations, size and weight of the building, adding a solar system to an existing building not built to include that purpose, and load-bearing capacity of the existing foundation. 

What should I do next?

Having a thorough assessment of the soil and building conditions around your home or investment prior to any construction or extensive renovation is essential.

If you think your home, investment, or business requires underpinning and foundation repairs, or you are planning on renovations or installing a swimming pool close to your home, call our expert team to arrange a free consultation – 0429 999 478

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