A regional aquatic centre is a major public asset, and when one starts showing signs of movement, the questions come quickly. Warwick Indoor Recreation and Aquatic Centre had reported settlement and level variation, and there was an understandable concern that the pool shells might be deteriorating where nobody could see. The owner, Southern Downs Regional Council, faced the familiar fork: commit to intrusive investigation and possible major works, or find a way to understand the structure first.

South-East Scanning was engaged to take that first look while the pools were drained for maintenance. The job was to assess the condition of the Olympic pool, children's pool, rapids pool, and surrounding suspended slab, identify any voiding, moisture pathways, or loss of support, and do it all non-destructively, so the investigation answered the question without adding to the repair bill.

The Brief: Confirm Or Rule Out, Before Spending

The council had observed level variation in parts of the facility and wanted to know whether it signalled a structural problem beneath the pool shells. That is exactly the kind of question where guessing is expensive. Cutting into a pool shell to investigate is costly, disruptive, and, if the structure turns out to be sound, avoidable. The brief was to use non-destructive methods to characterise the pool shells and slabs, then advise where, if anywhere, intrusive verification was actually warranted.

Our Approach: One Survey, Read At Three Depths

We can build a detailed picture of a pool shell without touching it, by combining methods that each look at a different depth and reading them together. On this job that meant pairing high-frequency concrete scanning with a dual-frequency GPR system, so a single visit covered everything from the reinforcement near the surface down to the conditions well beneath the slab.

One Survey, Three Depths

High-frequency scanning reads the rebar, while the dual-frequency GPR reaches the intermediate and deep zones beneath the shell.

High-frequency concrete scanning with an IDS C-Thrue, run on a 250 by 250 mm grid, mapped the reinforcement layout, cover depth, and slab consistency in the upper shell. A Leica DS4000 dual-frequency GPR then did the deeper work: its 900 MHz antenna read intermediate slab conditions, pipework, expansion joints, and localised dielectric variation, while its 200 MHz antenna reached the deeper zone where voiding, washout, and loss of support would show up. Grid-based C-scans were collected where the geometry allowed, and representative linear B-scans were used on the curved and figure-eight sections. Everything was processed in Geolitix.

Two honest notes on method. First, the facility is indoors, so satellite positioning was not available; the data was aligned using relative positioning rather than full georeferencing, which is appropriate for this kind of condition assessment. Second, the pools had only recently been drained, so residual moisture remained in the shells and surrounds. Moisture affects how radar behaves, and we read the data with that in mind. GPR is an indirect, interpretive method: it reveals patterns and changes, but it does not confirm material type, corrosion, or structural integrity on its own. Where something needs to be certain, intrusive verification is the next step, and we say so.

Reading The Colour Maps

The radar results are presented as colour maps where cool blues are weak, consistent returns and warmer colours are stronger ones. A neat, repeating grid of strong lines is simply the reinforcement, the signature of a well-built, uniform slab. What draws attention is not a single bright spot but a pattern: a diffuse, noisy, or disrupted zone that breaks the regular rhythm of the data.

Reading The Data

A regular grid indicates consistent construction; a localised noisy zone is indicative, by observation, of changing subsurface conditions and flags an area for a closer look.

What We Found, Pool By Pool

Across the facility, the story was reassuring. Most of the structure produced clear, coherent, repeatable radar responses, consistent with well-constructed reinforced concrete and showing no evidence of widespread voiding, washout, or structural instability. The interest, where there was any, was localised.

Findings Across The Facility

Sound overall, with a short watch-list. Schematic layout only, not to survey position.

The Detail

What It Meant For The Client

The most useful finding was not a problem, it was the absence of one. The data did not support the fear of widespread deterioration. The Olympic pool in particular read as the most consistent of the structures, and there was no evidence of large voiding or major loss of support anywhere in the scanned areas. For an asset owner staring down the possibility of major intrusive works, that is a genuinely valuable result: it took the worst-case scenario off the table on the available evidence.

That said, an honest assessment does not hand over a clean bill of health from non-destructive data alone, and we did not. Three localised areas earned a place on a watch-list: the deeper reflections toward the Olympic pool deep end, the noisy response along the perimeter where settlement had been reported, and the comparatively noisy exterior shell of the rapids pool. The perimeter response is the one most relevant to the council's original concern. GPR cannot tell us whether that level variation came from historical settlement, construction tolerances, infiltration, or ground movement, only that conditions there differ from the surrounding perimeter. Confirming the cause needs a closer look, and where movement is involved that means a structural engineer and a formal level survey, not a radar report.

The Path Forward

Rather than a blanket recommendation to investigate everything, the findings supported a proportionate, staged plan:

• Hold off on broad intrusive works. The data does not justify widespread coring across the Olympic, children's, or rapids base slabs.
• Verify the watch-list, if and when it matters. Targeted core sampling or localised verification at the Olympic perimeter settlement zone, the deep end, and the rapids exterior shell, prioritised if movement continues or works are planned there.
• Bring in an engineer for the movement question. A structural engineering assessment and a level survey to determine whether active settlement is occurring at the reported perimeter zone.
• Monitor the interfaces. Keep waterproofing, perimeter joints, drainage, and overflow systems maintained, these are the usual moisture pathways in aquatic structures, and watch the settlement-prone perimeter for changes in level, cracking, or drainage behaviour.
• Use corrosion-specific testing if needed. If reinforcement corrosion or "concrete cancer" is suspected, half-cell potential testing or targeted verification is the right tool, GPR cannot confirm corrosion on its own.

Why This Matters

Non-destructive investigation is often framed as a way to find problems. Just as often, its value is the opposite: confirming that a structure is sound, and replacing a vague, expensive worry with a short, specific list of things to check. For a council managing a busy public facility on a budget, knowing where not to spend is worth as much as knowing where to.

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