Moving bulk quantities of dirt and compacting is a huge job and done properly can save you thousands of dollars . Usually the volume of fill is doubled when excavating. Some soil and clay structures in are areas have acid sulfate , beach sand, clay sands , rubble washed sands, and very poor fractured rock ,and our deeper rock layers are blue stone rocks . The mixture of soils and stone piling up on themselves for years has made up some crazy soft and hard layers in the hinterland. Some of these materials have a very poor structure and is very hard to re compact. Digging up these soils have soft outer layers then hard layers and then back to soft layers making construction difficult to get a good footing. Where detailed footing design is required in softer layers auger holes till hard depth is reached can go down as far as five meters in the lower areas of the Gold coast.