Ground conditions, clay and cracking in Craigieburn VIC

Craigieburn sits almost entirely on the Newer Volcanics basalt plain, with creek alluvium along the Merri Creek and Aitken Creek corridors and small bedrock inliers. The residual basaltic clay over it is documented as high plasticity and reactive, and the geological literature describes smectitic clay with strong swelling and shrinking properties, typically half a metre to three metres deep through this corridor. That is why cracking is the single most common thing we measure here. What we will not do is print a site class for the suburb, because AS 2870 classification is determined per lot from your own soil report and varies street to street.

Roughly 92 per cent of the locality is mapped as Newer Volcanics sheetflow basalt.

Residual basaltic clay is documented as high plasticity and reactive.

Smectitic clay with strong swelling and shrinking is typically 0.5 to 3.0 metres deep.

Land Subject to Inundation and Urban Floodway areas run along Merri Creek and Aitken Creek.

AS 2870 site class comes from your lot's soil report, not from a suburb wide figure.

More about Craigieburn

Written by our local inspection team from work carried out in Craigieburn. Licensed building practitioners.

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Ground conditions, clay and cracking in Craigieburn VIC: common questions

What site class is Craigieburn?

There is no valid suburb level answer. Your soil report gives the class for your lot and that is what the slab was designed from. Anyone quoting one class for the whole suburb is guessing at it.

So is cracking here inevitable?

Some seasonal movement is expected on reactive clay, and minor cracking with it. What matters is the width, whether the pattern suggests structural movement and whether it is still progressing, which is why we measure rather than describe.

What can I do about it?

Keep moisture around the footings as even as you can. That means working drainage, downpipes discharging away from the building, and not letting garden beds against the slab go through cycles of soaking and drying out.