Confirming the As-Built: Non-Intrusive Slab Investigation at a Waste Transfer Facility
When a slab fails, the first question is why. Drawings alone rarely have the answers.
HIGHLIGHTS
Complete slab construction resolved across the accessible floor area: two full layers of reinforcement, slab thickness and surface-finish rebar, with no core taken.
Zones where the top layer of reinforcement was missing, identified and mapped against the structural grid.
Every finding delivered as annotated CAD drawings and thickness heat maps, giving the engineering team defensible data to act on.
BACKGROUND
A section of the facility's slab had failed in shear. For the engineers, the question was not only how to repair it, but why it had happened, because the cause determined the cure. Three explanations were possible: the slab had been inadequately designed, it had been built differently from the design, or it had been damaged in service by the heavy plant and bulldozers operating across the site. Each pointed to a different response, and none could be ruled out without knowing what was actually in the slab.
A materials testing partner engaged TRACE to establish the true construction of the reinforced concrete first-floor slab and compare it against the available drawings. Breaking out concrete across an operational facility was not practical, so the investigation had to be entirely non-intrusive.
OBJECTIVES
The survey set out to answer one critical question: was the slab poorly designed, incorrectly constructed, or damaged through use? To get there, TRACE confirmed the slab thickness and reinforcement arrangement against the available drawings, identified any differences in the as-built construction, and assessed whether the slab showed signs of alteration or damage in service.
SOLUTION
The survey used a Proceq GS9000 ground-penetrating radar (GPR) system, a high-resolution array operating across a 500–3000 MHz frequency range for detailed imaging of the first metre of concrete, scanned on a regular orthogonal grid at 0.8 m centres wherever access allowed. Stored materials, obstructions and standing water from rainfall meant the full floor could not be reached, so TRACE recorded exactly which areas were surveyed.
TRACE's analysts then processed the data off-site, calibrating it using the hyperbola-matching method, which fixes the radar's depth readings against the concrete itself, before interpreting it against known construction patterns to separate genuine deviations from noise. Rather than handing back raw radargrams, TRACE translated the findings into annotated CAD drawings and heat maps that answer the engineers' questions directly.
[ST1]Taken from the report. I've assumed your audience will value this level of KEY FINDINGS
Across most of the surveyed area the slab showed a consistent arrangement: an overall depth of approximately 250–600 mm, comprising a reinforced concrete structural slab of roughly 200–400 mm with surface finishes above. Two layers of reinforcement were detected at nominally 300 mm centres, with localised areas at 150 mm centres consistent with overlapping bars.
The key finding in this survey was unambiguous. In the defined zones, the top layer of reinforcement was absent, which was a clear departure from the expected arrangement, mapped precisely against the structural grid. The survey also identified reinforcement within the surface finishes above the structural slab and captured how slab thickness and finish depth varied across the floor as heat maps.
Some depth readings were affected by standing water on the day, and bar sizes cannot be determined by radar alone. Both were flagged in the reporting, so the engineers knew exactly where the findings were firm and where to read them with more caution.
BENEFITS
The engineering team gained a clear, structured picture of what was actually built, rather than a folder of raw scans to interpret for themselves. Because the survey was non-intrusive, that came without cutting into the slab, or the disruption that breaking out concrete would have caused in a live, operational facility.
OUTCOME
And it answered the question the engineers came with. The slab had been well designed and well built, thick and heavily reinforced. But where front loaders repeatedly pushed waste across the floor, the machines had gouged out the top layer of concrete and the bars within it. That top mat was what resisted punching shear; with it stripped away, and under the heavy, dynamic loads of the plant, the slab could no longer do its job. The cause lay not in the design or the construction, but in what operational use had done to the structure, and TRACE's survey mapped exactly where, giving the engineers a defensible basis for the decisions that followed.
Additionally, although outside the survey's scope, the same GPR data held early indicators of corrosion risk elsewhere in the slab, deterioration that could drive a future problem if left unchecked, giving the client sight of an issue still on the horizon.
[ST1]Again, let me know if too detailed for your audience, happy to simplify.l, but can take out some of the granularity if too much
[ST2]i have tried to simplify this from the report using google. Let me know if this needs adjusting
