The earthworks — excavation, backfill and compaction — are the part of pool removal that determines whether the job is done properly. A pool that has been removed but poorly backfilled will settle over time: you’ll see surface depressions within twelve to eighteen months, drainage problems in wet Southern Highlands winters, and potentially structural issues if you ever build over the site.
Proper backfill and compaction is not a luxury item in pool removal — it’s the fundamental quality standard that separates a job done right from a job that causes problems for years. Southern Highlands Pool Removal arranges this work through licensed excavation contractors who understand the specific soil conditions in the Wingecarribee Shire.
Why Backfill and Compaction Quality Matters So Much
When an inground pool is removed, the void — typically 1.5–2.5m deep — needs to be filled with material that, once compacted, behaves similarly to the undisturbed soil around it. If the fill isn’t compacted properly, a number of things happen:
Settlement. Fill material under load (even just the weight of soil above it, plus seasonal wet/dry cycles) will compact over time. If it wasn’t pre-compacted during the removal, it compacts under gravity over the following months and years — creating a visible depression at the surface. In clay soils like those found in parts of the Southern Highlands, this process can be significant.
Drainage problems. A void filled with loose material can act as a sump — collecting groundwater from the surrounding soil and creating a persistently wet area on the surface. Drainage holes in the pool base (essential for partial fill-ins, also present in full removal) need to be properly placed and the fill material needs to allow water to pass through.
Building restrictions. If you intend to build over the site, inadequate compaction documentation may mean your builder or engineer can’t certify the site as suitable for a slab or structure without additional testing and remediation.
The Southern Highlands Soil Context
The Wingecarribee Shire has variable soil types that affect backfill and compaction requirements:
Reactive clay soils. Parts of the Highlands, particularly in the Moss Vale and western plateau areas, have expansive clay soils that expand when wet and shrink when dry. This soil movement (classified by reactivity index) affects compaction behaviour and the fill specifications needed to achieve a stable result. On highly reactive clay sites, the backfill specification may need to account for this movement.
Sandy loam and topsoil zones. Other parts of the Highlands — particularly in valley areas and the eastern escarpment fringe around Robertson — have better-draining loamy soils that compact more predictably.
Fill quality. The quality of imported fill material matters. Clean, well-graded fill without excessive clay content compacts well. Poor-quality fill (high clay content, contamination, large particle size variations) compacts poorly and creates future problems. We specify the fill quality in the job documentation.
The Excavation and Backfill Process
Preparation
Before backfill begins, the pool void needs to be in the right condition:
- Pool shell fully demolished or removed
- Drainage holes punched through the base (for both full and partial removal)
- All plumbing stubs capped below finished surface level
- Any unstable material or organic material removed from the void walls
Drainage Layer
A drainage layer of coarse gravel or clean crushed rock is typically placed at the base of the void — over the pool base (where it remains) or over the compacted sub-base in a full removal. This layer ensures groundwater entering the void can drain through rather than ponding.
Backfill in Layers
Fill material is placed in layers — typically 200–300mm uncompacted depth — and each layer is mechanically compacted using a plate compactor or vibrating roller before the next layer is placed. The maximum lift depth varies depending on the compaction equipment and soil type; following the correct lift depth is one of the most critical quality control steps.
Fill Material Options
- Imported clean fill. Screened, well-graded fill material sourced from a quarry or approved source. The most reliable option for consistent compaction.
- Crushed concrete rubble (to approved quantities). Broken concrete from the demolished pool shell can be used as fill to a maximum percentage set by the applicable development standard. Clean concrete rubble compacts well and is cost-effective.
- Original excavated material. If the material removed when the pool was originally installed was retained on-site and is clean, it can sometimes be reused as fill.
Compaction Testing
For customers who require documentation of compaction quality — primarily those planning to build over the site — we arrange compaction testing by a geotechnical tester who uses a nuclear density gauge or sand replacement test to confirm that the fill has been compacted to the specified percentage of maximum dry density. Test results are provided in a report format suitable for building approval purposes.
See our guide to building over a filled-in pool for what compaction specifications are typically required for different future uses.
Surface Finish
After compaction, the surface is graded to the required level (typically matching the surrounding yard level, with a slight fall for drainage), and left ready for your chosen surface treatment.
Compaction Standards for Different Uses
| Intended Future Use | Typical Compaction Standard |
|---|---|
| Lawn or garden only | 90–93% standard Proctor compaction |
| Vehicle access or light paving | 93–95% standard Proctor |
| Concrete slab (light use — shed, patio) | 95–98% standard Proctor |
| Building slab (residential structure) | 95–100% standard Proctor + engineer certification |
| Pool replacement (new pool) | Not applicable — full excavation of fill required |
These standards are indicative. Your structural engineer or building certifier will specify the exact requirement for your project.
Frequently Asked Questions — Pool Excavation and Backfill
What happens if the backfill isn’t compacted properly? Surface settlement within 12–18 months of the removal is the most common outcome — a visible depression where the pool used to be. In worse cases, the depression can become significant enough to cause drainage issues or create a hazard. Re-doing compaction after the event requires re-excavating the area, which costs more than doing it properly the first time.
Do I need compaction testing if I’m just putting lawn over the filled area? Not strictly required for lawn or garden use, but it’s a relatively low-cost addition to the job (typically $300–$600 for a test) that gives you documented assurance the fill is stable. It also helps if you ever change your mind and want to build on the area later.
What fill material is best for pool backfill? Imported clean, well-graded fill (free of clay balls, organic material and large stones) is the most consistent option. Crushed concrete rubble is also effective and can reduce costs by using material already on-site. We specify and source the fill material as part of the job.
How long does the backfill settle before the surface is stable? With proper compaction, there should be minimal settlement — perhaps 10–20mm over the first wet season for even well-compacted fill, due to moisture redistribution. Settlement significantly beyond this (50mm+) is a sign of inadequate compaction.
Can I request compaction certificates for my records even if I’m not building? Yes. We can arrange compaction testing on any job regardless of the intended future use. Some customers want this documentation for insurance or future sale purposes.
Want to ensure your pool removal earthworks are done to standard? Get a free on-site quote.