What Is the Geology of Melbourne

melbourbe geology

Have you ever hired a builder or plumber to work on your property? If so, you might have been told at one point or another: “Your house is moving.” We’ve actually had clients who have heard- and misunderstood this phrase so many times. This happened so often that they genuinely believed their house would end up on the next block!

If a professional has ever uttered this phrase about your house, there’s no need to worry. It’s very common for footings to experience some extent of movement. This also is known as “differential foundation movements,” and is rarely lateral.

Reactive soil, common in Melbourne, can cause differential foundation movements. It can become serious from time to time.

How and Why Reactive Soil Moves?

“Differential foundation movements” occur because the foundation which supports footings is only soil. The Melbourne soil has a clayey texture. It is made up of microscopic particles that interlock with each other to form plates. With clay, water collects between the plates, which is why it’s always moist. Clayey foundation soil can certainly support your home’s footings. But it can also be “reactive,” due to its moist consistency. “Reactivity” is the word used to describe the tendency of foundation soil to change its volume. It shrinks or swells due to the variation in moisture content.

A map of Melbourne geology
A map of Melbourne geology

When clay soil absorbs extra water, the water floats between the clay particles. Water pushes the particles apart causing the soil to expand. As the soil swells, it applies upward pressure to the footing causing a ‘heave’ to occur.  On the other hand, clay soil shrinks when it loses water. this causes footings to collapse, ultimately leading to “settlement”. In this light, the more “reactive” the soil is, the more your home’s footing will move.

Cracking in soil due to shrinkage of reactive soil
Shrinkage effects in reactive soil

Learn more about effect of trees on footing Here.

Now you know that if a professional ever tells you that “your house is moving,” all he means is that you have reactive foundation soil. Whilst slight footing movements are completely normal, excessive differential footing movements should be taken seriously and assessed properly by forensic engineers.

What is Efflorescence and How to Prevent it (simplified)


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