A recent article in SMH has the optimistic heading "Hornsby Quarry set to be filled with North Connex spoil from October". The detail in the article gives a less favourable view. Quotes from the article include:
The 100-metre deep pit will finally become a little shallower from October when it is due to start being filled will spoil from the construction of NorthConnex. Residents have been warned that it will not be a pleasant process. The spoil haulage is expected to last up to 28 months and is not due to be completed until the end of 2018. At its peak, there will be 70 trucks travelling through Hornsby every hour from the excavation site to the pit. But even after the NorthConnex soil has been dumped, the pit will still only be one-third full.
The cross section diagram off the Roads and Maritime website suggests the pit will be filled well above one third, but we don't know how accurate that is. RMS will probably say the diagram is just indicative.
I have wondered for years where all the spoil hauled from recent excavations goes, eg M2, North West Rail Link, even The Module three stories deep hole now being dug. One assumes there is a commercial market for good quality Australian soil, but it's just a shame that the authorities can't mandate that all significant spoil goes toward filling the quarry.