A geotechnical report after a pool fill-in typically costs $800-$2,500 (indicative range) and is essential if you might ever build anything permanent over the site. If the pool removal is purely for more backyard space and you will never build over the area, a compaction certificate from the contractor may be all you need. But for any future shed, garage, granny flat, or extension, a geotech report is the document that makes it possible, and getting it commissioned during the fill job is far cheaper than retrofitting it later. Our pool excavation and backfill service includes staged compaction; speak with the contractor about arranging testing at the time.
What a geotech report actually tests
A geotechnical investigation for a pool fill-in site typically includes:
Compaction testing. The most common method is the nuclear density gauge test or sand-replacement test, checking the dry density of compacted fill layers against a reference standard. The two standards used in Australia are:
- Standard Proctor (AS 1289.5.1.1): The baseline. Most residential fill is specified at 95% Standard Proctor maximum dry density.
- Modified Proctor (AS 1289.5.2.1): A higher-energy compaction standard used when heavier loads are expected. Required for most garages and commercial slabs.
Layer-by-layer records. Good practice is to test each 150-200mm compaction layer as it goes in, not just the surface. A reputable contractor will pause and allow testing at each stage. Before fill is even ordered, our pool fill volume calculator guide explains how to work out the total cubic metres a given pool void needs, which is the number the layer-by-layer testing plan is built around.
Soil classification. The report identifies the native soil type beneath the fill (clay, sand, silt, rock), which determines how a structural engineer will design footings for any future structure.
Site classification. For building purposes, the report may assign an AS 2870 site classification (A, S, M, H, E, or P), which tells the building certifier and engineer what reactive soil conditions are present.
Occasionally the investigation, or the excavation itself, reveals rock beneath the pool’s original footprint before the geotechnical picture is even complete; see our guide on rock excavation surprises during pool removal for how that affects backfill depth, cost and timeline.
The reference engineer for finding a qualified geotechnical professional is Engineers Australia find an engineer.
A geotechnical report assesses how the placed fill behaves for footing design, which is a separate question to whether the fill itself was legitimately sourced and classified before it went in the ground; see our guide on VENM vs ENM clean fill rules for pool backfill for that side of the paperwork, and our guide on where pool backfill dirt actually comes from and what it costs for the sourcing and pricing side before it’s even delivered to site. Where the fill is the pool’s own demolished concrete rather than imported material, our guide on reusing crushed pool concrete as backfill covers the rules and compaction considerations specific to that option.
When one is needed vs nice-to-have
| Situation | Geotech report? |
|---|---|
| Turf or garden only over fill | Not required; compaction certificate usually sufficient |
| Light garden shed (exempt development) | Nice-to-have; certifier may not require it |
| Larger shed or carport needing approval | Likely required by certifier |
| Garage, granny flat, or habitable room | Required in nearly all cases |
| Sloping block or known problem soils | Recommended regardless of structure type |
| Future home sale | Strongly recommended; supports disclosure |
For sloping Lake Macquarie blocks where fill retention is involved, see pool removal on sloping blocks. For flood-prone areas in Maitland and the Hunter where fill height limits apply, see flood-prone pool removal in Maitland.
Typical cost & who commissions it
Indicative costs for geotechnical work on a residential pool fill-in site in the Hunter region:
- Compaction testing only (contractor-arranged, during fill): $300-$700, usually billed as part of the removal job
- Post-fill geotechnical investigation (full bore and report): $800-$2,500 depending on depth, number of test holes, and report complexity
- Retrospective investigation (fill done years ago, unknown quality): $1,500-$4,000+ as accessing and assessing older fill is more complex
Who commissions the report depends on the situation:
- During the removal job: The pool removal contractor often arranges compaction testing as part of their quality process. Ask for this to be included in the quote.
- For a building project: The builder or owner-builder commissions a geotechnical engineer before engaging a structural engineer for footing design.
- Retrospectively for sale purposes: The homeowner commissions it as a disclosure document for buyers.
The hidden costs of pool removal guide covers geotechnical testing as one of the line items people often forget to budget for.
What to keep on file for the future buyer
Buyers and their building inspectors will want evidence that the site is safe to build on. Keep:
- The original pool removal approval (DA, CDC, or council letter)
- The final inspection certificate from the certifier or council (see final sign-off and inspection after pool removal)
- Layer-by-layer compaction test results from the fill job
- The geotechnical report if one was commissioned
- Any structural engineer’s footing notes if a structure was subsequently built
Store these documents with your property title documents. They have no expiry date and add tangible value when you sell, as buyers avoid the expense of commissioning their own investigation. See selling a house with an old pool for how pool site documentation affects buyer confidence.
For more on what you can build over the filled site, see building a shed or garage over a filled-in pool and building over a filled-in pool.
FAQs
Can I get a compaction certificate without a full geotechnical report?
Yes. A compaction certificate (from a contractor or a materials testing company) confirms that the fill was placed to a specified compaction standard. A full geotechnical report goes further and classifies the subsoils, assesses reactive soil conditions, and produces an AS 2870 site classification. For anything more than a light shed, you want the full report.
How deep does the testing go?
For a pool fill-in, testing should cover all filled material, which is the depth of the original pool, typically 1.5-2.5 metres. The engineer will also test native soil below that depth to understand bearing capacity for footings.
How long does a geotechnical investigation take?
Site attendance is usually half a day. The written report follows within 1-2 weeks. For a building project with a known timeline, commission the investigation early in the design process.
What does AS 2870 site classification mean?
It is the Australian Standard for residential slabs and footings. It classifies soil reactivity from A (least reactive, usually sands and gravels) to E and P (highly reactive or problem sites). The classification determines what slab and footing type a structural engineer will specify.
Is a geotech report needed for a partial fill-in (pool shell left in place)?
Often yes, particularly if any structure is planned. The pool shell was not designed as a footing and its long-term structural behaviour as a buried void-former needs to be assessed by an engineer before building above it.
Related reading
- Compaction testing after pool fill: what the certificate covers
- Building a shed or garage over a filled-in pool
- Building over a filled-in pool: full guide
- Final sign-off and inspection after pool removal
- Pool excavation and backfill service
- Selling a house with an old pool
- Get a free quote