How to spot bad earthworks before it gets structural.
Earthworks is the one trade whose mistakes are invisible on handover day and obvious four years later. The fill under your slab either got compacted or it did not, and you cannot tell by looking. What you can do is read the symptoms early, while the fix is a few thousand dollars instead of an underpinning job. Here is what we look for on a Casey block.
Settlement - the ground is still moving.
Look for a soft or spongy feel underfoot after rain, a driveway or path that has dropped a few millimetres against a fixed edge like a garage slab or a kerb, hairline cracks that run in a straight line rather than randomly, and puddles that appear in the same spot every time. On a new build the tell is often the driveway meeting the garage - if there is a lip forming within the first two years, the fill under it was never properly compacted. None of these are cosmetic. They are the fill telling you it is still settling, and it will keep going for years.
Uncompacted fill does not settle evenly and it does not settle quickly. It creeps, usually most in the first three to five wet seasons, and it creeps most where the fill is deepest. That is why the corner of a driveway drops and the rest does not - one end sits on cut, the other on 800mm of fill that got two roller passes instead of eight. In the newer Casey estates through Clyde North and Cranbourne East, where whole blocks are engineered fill over old farm paddock, this is the defect we see most.
Cracking - reading the pattern.
The pattern tells you. Random spidery cracking across the surface with no displacement is usually a concrete issue - shrinkage, a poor mix, or curing too fast in summer. A single straight crack with one side sitting lower than the other is a sub-base failure, and that is earthworks. Cracks that open in summer and close in winter are reactive clay moving under a sub-base that was never thick enough for a Class M to H1 site. In the Endeavour Hills and Hallam clay belt, that third pattern is the one we see most, and re-topping the concrete without fixing the base just buys you three years.
Casey's north-west clay swells 30-50mm through a season. That is not a defect, it is the soil doing what AS 2870 says Class M to H1 soil does, and the design is supposed to account for it. A driveway built on 100mm of crushed rock over that clay will crack. The same driveway on 200mm of properly compacted sub-base over a stabilised subgrade will not. The difference in build cost is a few thousand dollars; the difference in outcome is ten years. Our driveway preparation page sets out the depths we actually use in each soil zone, and Endeavour Hills has the local detail.
Water in the wrong place.
Because the finished surface levels are wrong, and it is the single most common defect we get called to fix. The ground next to a slab should fall away from the building at a minimum of 50mm over the first metre, and surface water should never be directed toward the footings. When a pad is trimmed to look flat rather than shaped to fall, or when topsoil is later spread back over the top and kills the grade, water sits against the edge beam. On reactive clay that is genuinely serious - persistent moisture at one edge of a slab and dry soil at the other is what causes differential movement and structural cracking.
The classic Casey version: landscaper spreads 150mm of garden soil against the house after handover, burying the slab edge and reversing the fall. The earthworks were fine. The grade is now wrong and the warranty conversation is a mess because two trades each blame the other. If your block has this, the fix is usually a day of re-grading plus an agricultural drain, in the $2,500-$6,000 range, and it is worth doing before the next winter rather than after. Drainage trenching covers how we cut the aggie line and tie it to a legal discharge point.
A four-year-old driveway in Hampton Park.
Owner called about a 70m² concrete driveway with a 25mm step where it met the garage slab, one straight crack two-thirds of the way down, and a puddle that never dried. Built four years earlier by the volume builder's subcontractor. Reactive clay, Class H1.
What we found on excavation: 90mm of crushed rock where the engineer's detail called for 200mm, placed directly on unstripped topsoil that still had grass roots in it. No stabilisation. The pad had been trimmed flat, so the fall toward the street was about 4mm per metre where 20mm would have been sensible. Everything visible was a symptom of one decision made in one afternoon four years earlier.
The repair: break out and cart away the existing slab (three tipper loads at $340), strip 300mm of contaminated subgrade, lime-stabilise, rebuild 200mm of sub-base in two compacted lifts with a density test, re-grade to a proper fall, and hand back a base ready for the concreter. Earthworks $8,900. New concrete by the concreter, another $9,400. Total about $18,300 to fix what would have cost roughly $2,800 extra to build correctly.
That ratio - roughly six to one - is consistent across every one of these we do. It is the reason the pricing guide shows what a proper sub-base costs rather than what the cheapest one does, and why the settlement and aftercare guide is worth reading in the first two years of a new build, not the fifth.
The test results are the only real proof.
Ask for the compaction test results, and ask for them before the slab goes down, not after. A properly executed controlled-fill pad in Casey has density testing to AS 1289 at a frequency set by the engineer or by AS 3798, typically one test per 300 cubic metres per lift or better on a domestic pad. If the contractor cannot produce a lab report with the site address, dates, the target density and the achieved result, then nobody actually knows what your house is sitting on. A verbal 'yeah we rolled it' is not a test.
And on the repair question: some of it, at a price. Surface grading, drainage correction, driveway sub-base rebuilds and retaining a failing batter are all fixable after the fact - expect $3,000 to $18,000 depending on scope and access. What is very hard to fix is uncompacted fill directly under a slab, because the only real remedies are underpinning or resin injection, and those are $25,000 upward and involve an engineer. That asymmetry is the whole reason we push people to get the testing done at pad stage. Ten minutes of test cost at the right moment saves a five-figure problem five years later.
If you are mid-build right now and reading this because something looks off, get a second opinion before the next stage locks it in. We will look at a pad and tell you honestly whether it is a problem, and we say "that is fine, leave it alone" more often than not. See site cut and fill for how a pad should be built, or the local trades directory if you need a geotech or an engineer rather than us.
Casey suburbs we cover.
Warning-sign questions.
What are the early warning signs of badly compacted fill?
Look for a soft or spongy feel underfoot after rain, a driveway or path that has dropped a few millimetres against a fixed edge like a garage slab or a kerb, hairline cracks that run in a straight line rather than randomly, and puddles that appear in the same spot every time. On a new build the tell is often the driveway meeting the garage - if there is a lip forming within the first two years, the fill under it was never properly compacted. None of these are cosmetic. They are the fill telling you it is still settling, and it will keep going for years.
How do I know if my site cut was done properly in Casey?
Ask for the compaction test results, and ask for them before the slab goes down, not after. A properly executed controlled-fill pad in Casey has density testing to AS 1289 at a frequency set by the engineer or by AS 3798, typically one test per 300 cubic metres per lift or better on a domestic pad. If the contractor cannot produce a lab report with the site address, dates, the target density and the achieved result, then nobody actually knows what your house is sitting on. A verbal 'yeah we rolled it' is not a test.
Are cracks in my driveway a soil problem or a concrete problem?
The pattern tells you. Random spidery cracking across the surface with no displacement is usually a concrete issue - shrinkage, a poor mix, or curing too fast in summer. A single straight crack with one side sitting lower than the other is a sub-base failure, and that is earthworks. Cracks that open in summer and close in winter are reactive clay moving under a sub-base that was never thick enough for a Class M to H1 site. In the Endeavour Hills and Hallam clay belt, that third pattern is the one we see most, and re-topping the concrete without fixing the base just buys you three years.
Why is water pooling against my house after new earthworks?
Because the finished surface levels are wrong, and it is the single most common defect we get called to fix. The ground next to a slab should fall away from the building at a minimum of 50mm over the first metre, and surface water should never be directed toward the footings. When a pad is trimmed to look flat rather than shaped to fall, or when topsoil is later spread back over the top and kills the grade, water sits against the edge beam. On reactive clay that is genuinely serious - persistent moisture at one edge of a slab and dry soil at the other is what causes differential movement and structural cracking.
Can bad earthworks be fixed after the house is built?
Some of it, at a price. Surface grading, drainage correction, driveway sub-base rebuilds and retaining a failing batter are all fixable after the fact - expect $3,000 to $18,000 depending on scope and access. What is very hard to fix is uncompacted fill directly under a slab, because the only real remedies are underpinning or resin injection, and those are $25,000 upward and involve an engineer. That asymmetry is the whole reason we push people to get the testing done at pad stage. Ten minutes of test cost at the right moment saves a five-figure problem five years later.
Something on your block not looking right?
Free look, honest answer. We say "leave it alone" more often than we quote a fix.