The photo below shows a subsidence which appeared in a commercial carpark in Girrawheen.
Below are 2 photos of the subsidence being excavated to locate the source.
The carpark is many years old and was constructed without the sub-base being totally cleared of vegetation which has resulted in a tree stump rotting away over the years, creating a cavity and then a subsidence.
We excavated the remains of the tree stump, backfilled with clean fill and compacted in 150mm layers.
A 200mm thick gravel base was installed, compacted and waterbound - followed by sealing with a bitumen tack emulsion and a 50mm thick layer of 10mm granite black asphalt/hotmix to seal.
The surface was cooled down with water and sprinkled with a layer of sand to allow for immediate traffic use. The sand prevents tyre scuffing on the newly laid surface.