What happens after the machine leaves.
Earthworks does not finish when the truck pulls out. The ground keeps responding for a couple of years, and what you do in the first twelve months decides whether that response is invisible or expensive. This is the aftercare conversation we have standing in the driveway on the last day, put in writing.
Why trenches sink, and how long for.
A properly backfilled trench - compacted in 150-200mm lifts as it goes up - is essentially finished settling by the time we leave, and any residual movement is a few millimetres over the first wet season. A trench that was simply bulldozed full of loose spoil will keep dropping for two to four years, most of it in the first two winters, and can lose 10-15% of its depth. That is why a 900mm-deep service trench across a lawn ends up as a visible 100mm gully by the second winter. The settlement is not bad luck, it is compaction that never happened.
The physics is simple. Excavated clay bulks up - the same material takes up 20-30% more volume loose than it did in the ground. Put it back loose and it looks like a slight mound, which is why the finished job seems fine. Two winters of rain drive the air out of it and it returns to something near its original volume, which is a trench-shaped depression. If that trench runs under a future driveway or path, you now have a straight crack waiting to happen along exactly that line. The early warning signs guide covers how to read that crack when it turns up.
Responsibility for it depends entirely on what was specified. If the quote said compacted backfill in lifts with a stated density and it settles, that is a workmanship issue and it sits with the contractor. If the quote said backfill only - which is what most cheap trenching quotes actually mean - then loose spoil going back in the hole is exactly what you paid for, and the settlement is contractual, not defective. This is why we write the backfill method into the quote rather than leaving it as an assumption. Read that line on any trenching quote you receive: it is usually the difference between two prices. Our drainage trenching scope states the lift thickness and the material every time.
Three things that are actually worth doing.
Three things, and none of them are expensive. Keep water moving away from the building - check after the first heavy rain that nothing ponds within a metre of the slab, and clear any silt that has washed into the fall. Get ground cover established on exposed batters before winter, because bare clay on a slope will rill and erode fast in a Casey June. And do not let anyone spread garden soil against the house and bury the slab edge. That is it. Most earthworks aftercare is just not undoing what was built.
That third one deserves emphasis because it happens on maybe a third of new builds. The pad was graded to fall away from the slab at 50mm over the first metre, exactly as it should be. Then a landscaper arrives, spreads 150mm of garden mix along the wall to make the beds look right, and the fall is gone. Now water sits against the edge beam of a house on reactive clay, which is the specific condition AS 2870 footing design is trying to avoid. Nobody did anything malicious and the outcome is still a five-figure problem in a decade.
Walk the block after the first genuinely heavy rain, ideally within the first three months. You are looking for one thing: standing water that has not gone within a couple of hours, particularly near the house, near a retaining wall toe, or in the middle of a new pad. Photograph it. That photo is worth more than any description when you call someone.
Protecting a fresh batter before winter.
Get cover on it before the rain arrives. A freshly cut clay batter in the City of Casey is at its most vulnerable in the six weeks between the machine leaving and anything growing. Options in ascending order of cost: sterile straw mulch and a hydroseed or couch runners at $8-$18 per square metre, jute mesh or coir matting pinned over the face at $25-$45 per square metre for steeper slopes, or a rock-lined batter drain at the toe if the catchment above is large. A silt fence at the base is required on any site with a building permit anyway, and it is the cheapest thing on the list.
Casey gets roughly 700-780mm of rain a year with the bulk of it May to October, and the storms that do the damage are the short intense ones in spring. A batter cut in April with nothing on it is looking at its worst six months first. Cut the same batter in October and grass will be holding it before winter. That sequencing is free and almost nobody thinks about it - the seasonal timing guide goes through the rest of the calendar logic.
On the sloping blocks through Narre Warren North, Harkaway and the older parts of Berwick, this matters more than anywhere else in the LGA. Those are the sites where a lost batter becomes a retaining wall you did not budget for.
A 34m service trench in Cranbourne East, two winters on.
New build, 34 metres of combined power and water trench from the street to the house across what would become the front lawn and the driveway line. Two quotes at the time: $2,150 and $3,400. The owner took the $2,150.
The difference between the quotes was one line. The cheaper one said "backfill trench". The dearer one said "backfill in 200mm compacted lifts, crushed rock to the top 300mm under the driveway line". Same machine, same days, about $1,250 of extra material and roller time.
Two winters later: a 60-80mm depression tracking the full length of the trench across the lawn, and a straight crack through the new concrete driveway exactly where the trench crossed it. The repair was 12m² of driveway broken out and carted ($1,100 earthworks, three-quarters of a tipper load), the trench re-excavated and rebuilt properly under the driveway line ($1,900), re-grading and topsoil on the lawn section ($1,400), and the concreter back for the slab section ($2,600). Total $7,000 to recover a $1,250 saving.
This is the most avoidable job we do, and we do several a year. When you compare trenching quotes, the number is not the thing to compare - the backfill line is. Rates for both approaches are on the pricing guide, and Cranbourne covers the local soil that makes this particular corridor so prone to it.
Living on a site that moves.
Not the pad itself, but the reactive clay around a finished house genuinely benefits from consistent moisture. AS 2870 designs footings for a soil that moves, and the damage comes from differential movement - one side of the slab bone dry while the other stays wet. In a Casey summer, a shaded south side stays damp while a north-west corner shrinks away, and that difference is what cracks cornices. Even, modest watering around the perimeter in a long dry spell, plus keeping large trees at a sensible distance, is real preventive maintenance on Class M to H1 sites.
The tree distance rule of thumb most engineers use is that a mature tree should sit at least its own mature height away from the footings on a highly reactive site, and further for known heavy drinkers. In Endeavour Hills and the Hallam clay belt, a large gum eight metres from a slab is doing more to your footings than anything the earthworks contractor did or did not do. That is not our trade to fix, but it belongs in the same conversation, and the local trades directory lists the arborists we work alongside.
Once the pad is right, the maintenance is genuinely light. Check the falls after big rain, keep cover on the slopes, keep the moisture even, do not bury the slab edge. Four habits, most of them free. Everything else is somebody else's trade. If you want the pad done right in the first place, site cut and fill is where that starts.
Casey suburbs we cover.
Settlement and aftercare questions.
How long does backfill take to settle after a trench in Casey?
A properly backfilled trench - compacted in 150-200mm lifts as it goes up - is essentially finished settling by the time we leave, and any residual movement is a few millimetres over the first wet season. A trench that was simply bulldozed full of loose spoil will keep dropping for two to four years, most of it in the first two winters, and can lose 10-15% of its depth. That is why a 900mm-deep service trench across a lawn ends up as a visible 100mm gully by the second winter. The settlement is not bad luck, it is compaction that never happened.
What should I do with my block in the first year after earthworks?
Three things, and none of them are expensive. Keep water moving away from the building - check after the first heavy rain that nothing ponds within a metre of the slab, and clear any silt that has washed into the fall. Get ground cover established on exposed batters before winter, because bare clay on a slope will rill and erode fast in a Casey June. And do not let anyone spread garden soil against the house and bury the slab edge. That is it. Most earthworks aftercare is just not undoing what was built.
Do I need to water a new fill pad in summer?
Not the pad itself, but the reactive clay around a finished house genuinely benefits from consistent moisture. AS 2870 designs footings for a soil that moves, and the damage comes from differential movement - one side of the slab bone dry while the other stays wet. In a Casey summer, a shaded south side stays damp while a north-west corner shrinks away, and that difference is what cracks cornices. Even, modest watering around the perimeter in a long dry spell, plus keeping large trees at a sensible distance, is real preventive maintenance on Class M to H1 sites.
How do I stop a new batter or slope eroding?
Get cover on it before the rain arrives. A freshly cut clay batter in the City of Casey is at its most vulnerable in the six weeks between the machine leaving and anything growing. Options in ascending order of cost: sterile straw mulch and a hydroseed or couch runners at $8-$18 per square metre, jute mesh or coir matting pinned over the face at $25-$45 per square metre for steeper slopes, or a rock-lined batter drain at the toe if the catchment above is large. A silt fence at the base is required on any site with a building permit anyway, and it is the cheapest thing on the list.
Who is responsible if backfill settles after the job is done?
It depends entirely on what was specified. If the quote said compacted backfill in lifts with a stated density and it settles, that is a workmanship issue and it sits with the contractor. If the quote said backfill only - which is what most cheap trenching quotes actually mean - then loose spoil going back in the hole is exactly what you paid for, and the settlement is contractual, not defective. This is why we write the backfill method into the quote rather than leaving it as an assumption. Read that line on any trenching quote you receive: it is usually the difference between two prices.
Trench dropped? Batter washing away?
Most aftercare fixes are a half-day and a few hundred dollars if you catch them early. Free look either way.