Ground heave is the bane of any builder, developer, or homeowner’s life. The two evil twins – Heave & Subsidence – cause huge amounts of damage to properties around the world and are set to only get worse as population growth forces increased building on substandard land.

But what is ground heave and how do you avoid it? Let’s find out.

Ground heave happens with excess water

Except in the case of earthquakes, almost any ground movement happens due to an excess or lack of water. Channels in valleys, for example, are often formed due to sudden heavy rains that cause waterways to significantly overflow and cut paths through the ground.

A little closer to home, ground swell tends to happen in the wetter months as rainfall gets absorbed into the soil around properties. How much water gets absorbed depends usually on the total mineral composition of the soil – the biggest offenders are clays.

Imagine a dried sponge: as you add water to it, it begins to expand as it absorbs that water. It’ll usually expand at the same rate all over – so that if you were to put something small on top of the sponge it would be lifted in a regular way. But soil being composed of a variety of minerals means you have the equivalent of a huge variety of sponges (all with different absorption rates) soaking up water – this is what’s difficult to account for.

Buildings have to be built on something

The reason why this is such a problem is that any building has to be built on something. If you’ve ever seen a rickety garden shed, it’s usually because it’s been plonked directly onto the garden soil. Even if you dig a big hole and fill it in with concrete, that concrete has to sit on top of and within soil that moves at variable rates.

You could mitigate the effects of movement by providing a suitably large counterbalance – by making the concrete-filled-hole big enough – but, like with ships on the sea, there’s only so much you can fight against the massive forces of nature.

Ground heave isn’t something you can avoid, but it is something you can work around.

The key is to build solid foundations

The huge concrete-filled hole proposed above is one way to mitigate the effects of ground heave, but then you’re forced to create an unnecessarily large cube of concrete – wasting time, money, and resources.

For lighter structures, a pile foundation is often a great way to keep costs down, mitigate the impact of floods in low-lying areas, and avoid damage from ground movement. These are posts with footings sunk into the ground, usually on each corner of the structure. With the structure built slightly floating above the ground, the ground is free to move underneath it without causing any trouble for the property itself.

This method has worked for millenia, but isn’t suitable for heavy structures. The piles end up becoming pressure points that get pushed further into the ground by the weight of the structure.

The solution in this case is to build a sturdy concrete foundation slab with an adequate void. We explore more on ground heave & concrete foundations here but, in short, the voids under a foundation slab behave in the same way that the voids in between the pile footings behave: they allow for movement without that movement coming into contact with the structure.

Use a suitable void-former

We’ve developed Clayboard to help builders create foundation slab voids easily, without additional expertise, and in a way that’s significantly better for the environment than alternatives. Learn more about Clayboard here, or get in touch to discuss making construction greener effectively.