Earthworks in Harlaxton, Toowoomba

Blocks that step down from the escarpment edge often carry clay on the high side and quarry stone not far below it, so the high-side cut is where breaker time tends to land. The low side is built up with compacted fill. Old slabs, rubble and dumped fill come out first where they stand in the way.

Grading follows. Where water runs onto the block from higher up, the falls are set to carry it past the house and not toward it.

The pad is compacted in layers to reduce settlement risk under a slab or shed, with testing where the engineering specification calls for it.

A retaining wall cut needs room behind the wall for drainage, so the dig goes deeper and wider than the wall itself. A washed-out driveway usually needs the soft, eroded base dug out and replaced with compacted road base.

Rock, buried footings and old pipes are what the operator watches for once the machine is on site.

A contractor with a mid to large excavator and a hydraulic rock breaker can dig through it. A rock breaker is a hammer attachment that fractures hard stone so the bucket can lift it out. A small machine will struggle and burn days on ground that a bigger one gets through quickly.

Old fill is a different problem. It can hide concrete, bricks, timber and buried rubbish, and it compacts poorly. The operator usually digs it out and replaces it with clean, compacted material. That is slower than a straight cut.

A written price before the machine arrives should include an allowance for rock and old fill, and say how breaking and removal are charged.

On the older streets around Downlands College, the side gate usually limits the job to a smaller excavator. Trenches, drainage and footings then run over a few days, not one big-machine day.

The machine comes with a driver who knows how deep to go and where the spoil, meaning the dug-out soil and rock, should end up.

A larger excavator suits a full house pad or a deep cut on one of the bigger blocks. The contractor picks the size after seeing the site, because the wrong machine either cannot reach or cannot dig.

A tipper truck to cart the spoil away is priced in the same job.

A house pad is the levelled, compacted platform a slab sits on. A shed pad does the same job for a shed, and it matters just as much, because a soft or uneven shed pad lets the frame twist and the doors stop closing.

Builders want the pad finished to the set levels before the slab crew turns up. A good operator works to those levels and leaves the surface firm and drained. If the builder cannot start until the ground is right, a pad that is out by a few centimetres costs everyone time.