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Reactive Soil: How it Affects the Way You Build


It’s always fun to build something which you can call your own. Once you own a piece of land, you can simply decide to start planning a construction, right? Wrong. There is something you need to consider that will dictate everything, from the viability of your plan to the design.


We are referring to the soil itself. It’s characteristics will influence everything, and it can reduce your dreams to rubble if you do not take them into account. The type you need to watch out for is what they call reactive soil.


What is Reactive Soil?


So what exactly is a reactive soil? While it sounds foreboding, it simply means the soil reacts greatly to moisture and other elements that can cause movement or abnormal shifting. When the soil is subject to changes is moisture, there is a tendency for it to either expand, contract, or even move. The degree it is affected by such a factor dictates how reactive the soil is.


How it Affects the Way You Build


Now this is the trouble with the soil’s reactivity. Using the wrong slab can cause painfully expensive damages to your property, which is why it is important to get expert opinion before starting to build any structure.


For example, when the soil becomes drenched, such as by burst pipes or heavy rainfall, it starts to become extremely reactive. When this happens, it will damage not only the slab used, but the house it sits on.


Extreme dryness is not a better situation either. Dry reactive soil will contract and causes movement in the ground which supports the slab. This will then cause it to either buckle or fall, and that spells disaster.

Building on Reactive Soils - Infographic


How to Classify Your Soil


In order for you to know if your soil is reactive or not, you will need an engineer who will conduct a soil test based on Australian Standard AS 2870/2011 - Residential slabs and footings. By doing this, you will get to know the degree of reactivity and what slab will work for whatever structure you wish to build.


Most reactive soils are classified as follows:

  • Class S (slightly reactive)

    • This type of soil is easy to manage as there is little reactivity to worry about.

  • Class M (moderately reactive)

    • In this classification, the ground movement isn’t too extreme and slabs can easily be constructed to adapt to it. The vertical movement can be around 20mm to 40mm depending on the season.

  • Class H (highly reactive)

    • This is a more serious type of soil and there needs to be proper drainage to ensure there won’t be excessive moisture. There will be special requirements in slab creation as well as pipe protection, which can be another source of moisture.

  • Class E (extremely reactive)

    • Very special attention needs to be given to this type of soil. It is the responsibility of both the builder and homeowner to take extra precautions when building on this site, as it is going to be a lifelong condition of the soil.


Aggravating Circumstances to Avoid


There are circumstances that you need to watch out for that can adversely affect reactive clays. All of which have something to do with the moisture content, and precaution needs to be done. Some of which are:

  • Long wet periods

  • Long dry periods

  • Water leaks from pipes, etc.

  • Uneven planting and watering

  • Air conditioners and hot water systems


As a homeowner, you need to be aware of the status of your soil and how you should work with it. After all, this is an investment you are looking at.

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