Concrete driveways on Sale's river-flat clay
Much of Sale was built on the flats where Gippsland's rivers meet the lakes. This guide explains how that ground behaves under a concrete driveway and what a good concreter will do about it.
Email: info@saleconcreting.com.au
How river-flat clay behaves
Alluvial clay near the Thomson, Latrobe and Flooding Creek is fine-grained and holds a lot of water. Through a wet winter it swells and softens; through a dry summer it dries out and pulls apart into wide fissures. A driveway placed directly over it heaves in July and settles again by March, and the slab eventually cracks across its weakest point, usually near the garage or where a downpipe discharges.
What should come out
The topsoil and the soft, wet upper layer of clay need to be dug out until the excavator reaches firmer ground. How deep that is varies from street to street and sometimes across one block. A test hole at the quote visit gives a good indication, and a concreter who has not dug one is guessing.
What goes back in
Class 3 or similar crushed rock goes down in thin lifts, each one vibrated tight, building a firm, free-draining platform for the slab. On softer clay the base is thicker, and geofabric may be used to keep the rock from pushing into the clay. The base should extend past the slab edges so they are supported too.
Keeping water away
Clay only moves when its moisture changes, so drainage is half the battle. Downpipes should discharge into the stormwater system, not beside the slab. Falls should carry water to pits, drains or the kerb, and garden beds next to the driveway should not be overwatered.
Sandy rises and old fill
Not all of Sale is clay. Higher ground and parts of Wurruk and Longford have sandy loam that compacts well but needs edge protection. Older blocks sometimes hide fill from demolished sheds, pools or tanks, which settles unevenly and must be removed.
Flood overlays
Some low-lying streets and rural blocks sit in flood or inundation overlays. Driveway levels there need to work with the house floor level and the way floodwater and stormwater move across the site.
Questions worth asking
Have you inspected the subsoil yourself? What excavation depth are you allowing, and what is the plan if the clay is softer than expected? What rock, how thick, and how is it compacted? What slab thickness and reinforcement for my vehicles? Where are the saw cuts? Where does the water go? Who arranges the Wellington Shire crossover permit?
Talk to a Sale concreter
Free site visits and written quotes from Sale out to Maffra, Stratford, Heyfield and Yarram. We publish no rates, because river-flat clay, removal and access vary on every Wellington Shire job.