Soil type classification is a very complicated area and there are several different classification systems based on the intended use and application of the data, be it agricultural, environmental, building and construction or general scientific understanding. While each of the systems attempts to do research and testing and create soil maps and charts, the specific soil conditions can vary significantly across even short distances as well as different depths. Therefore, for some applications an onsite soil test needs to be done (or several) to determine the exact conditions on the site. For other applications, a more general understanding from soil maps will be sufficient. Read on for a general overview of the soils underpinning Adelaide.
The Australian State of Environment (SOE) Report (2016) describes 14 common soil types found in Australia which are classified with reference to their source, water content, acidity, texture, chemical makeup and other factors.
Soil classes typically refer to the building properties of soils, specifically how they move and react to moisture changes. According to the Australian Standard AS 2870-2011, seven different soil classes are found in Australia, shown in the table below.
|A||Sandy or rocky sites with minimal movement from moisture changes|
|S||Slight ground movement due to moisture change (0–20 mm of surface movement)|
|M||Moderate ground movement due to moisture change (20–40 mm of surface movement)|
|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||Extreme rate of ground movement (over 75 mm of surface movement)|
|P||Soft soils, filled sites, collapsing soils, and other unclassifiable or problem sites|
The SOE data includes some broadly classified regions in Adelaide (from the map) which we’ve summarised below including the classification, a brief description, the percentage of this soil type of all Australian soils and a description of the areas of Adelaide and surrounds that the type covers;
A recent SA Department for Environment and Water report divides South Australia into 61 different soil types, ranging from volcanic ash soils to cracking clay soils to highly leached sands. This classification system is a bit different from the SOE data referenced above and reflects the fact that each state uses a different system and there is no national standard. However, this map doesn’t include Adelaide itself.
Adelaide is well-known for having highly reactive soil, also known as ‘Bay of Biscay’ soils. This clay soil shrinks significantly during dry spells and swells rapidly during times of heavy rainfall.
The affected parts of Adelaide include the heritage suburbs of Wayville, Westbourne Park and Goodwood where older buildings are particularly susceptible to structural damage from movement. The surrounding suburbs including Netherby, Kensington, Kingswood, Linden Park and Hectorville are also at risk. Newton, Hope Valley, Holden Hill, parts of Gilles Plains and Hillcrest are some of the worst suburbs. Hindmarsh and Keswick are also at risk with some experts estimating the ground movement in this region often exceeds 75 mm during periods of extreme drought or rainfall.
Building on reactive soil presents significant challenges. Modern building techniques can mitigate much of the movement of reactive soil, but older houses can often develop significant cracks during exceptionally dry periods.
For the best, long-lasting construction, start any build with the necessary knowledge. Soil type will influence the type of subfloor your builder chooses, and for highly reactive sites, you may need to hire a structural engineer to work out the correct solution.
If you’ve already moved into your new home and are worried about the potential effects of reactive soil on your structure, consider working with Urathane Solutions. Our team of experts has handled extreme structural problems in the past and can help you solve yours as well. Give us a call to schedule a consultation and find out why we’re the best option for foundation repair and underpinning in Adelaide and South Australia!