Retaining Wall Surveys

A retaining wall that’s failing rarely shows it until the problem is already serious. Cracking, bulging or a visible lean are often the final stage of a process that’s been developing unseen for years, whether that’s water pressure building up behind the wall, reinforcement corroding, or voids forming within the wall’s core. By the time these signs are visible, remedial work is usually more extensive, and more expensive, than if the issue had been caught earlier.

Different Wall Types, Different Risks

How a retaining wall is likely to fail depends heavily on how it was built. Mass gravity walls rely on sheer weight and thickness to resist pressure, so voiding or thinning within the structure is the main concern. Reinforced concrete walls depend on the condition and position of internal steel, meaning corrosion or displaced reinforcement is often the bigger risk. Gabion and crib walls are less prone to internal voiding but can suffer from displacement or loss of fill material over time. Because the failure mode differs by construction type, we approach each survey differently rather than applying a single standard method regardless of what kind of wall we’re inspecting.

Reading a Wall With GPR

Our surveyors scan the wall using Ground Penetrating Radar on a systematic grid, recording variations in the radar signal as it passes through the structure. On a reinforced wall, this lets us map reinforcement position and cover depth, similar to a ferro scan, but interpreted against the wall’s likely loading and drainage conditions. Where a wall incorporates post-tensioned construction, we can extend the survey to include Locating Post-Tensioned Tendons, identifying their position before any drilling or coring takes place. On a mass gravity wall, we’re looking primarily for internal voiding, delamination or moisture ingress that could be weakening the structure from within. Wall thickness is measured as part of the same survey, giving a fuller picture of whether the wall still meets its original design specification.

Deliverables You Can Act On

You’ll receive a report and CAD drawing showing wall thickness, any voids or defects identified, and, where reinforcement is present, its approximate position and depth. Rather than a generic pass/fail summary, our findings are set out so a structural engineer can assess the wall’s remaining condition against its original design intent, informing whether the right next step is monitoring, targeted repair, or more significant remedial work.

Subvision Surveys carries out retaining wall surveys alongside our wider GPR and Sub-Surface Voiding detection services, so if a survey uncovers wider ground movement or drainage issues beyond the wall itself, we’re equipped to investigate that too rather than referring you elsewhere.

Get in touch to discuss a retaining wall survey for your site, or call 0333 920 942.

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RETAINING WALL SURVEYS FAQ’S

Retaining walls often fail from the inside out. Water pressure building up behind a wall, reinforcement corroding within concrete, or voids forming in the wall’s core can all weaken a structure long before any crack, bulge or lean becomes visible. By the time a defect shows on the surface, the underlying problem has often been developing for years. This is why a visual inspection alone can miss serious issues, and why a GPR survey, which looks at the wall’s internal condition rather than just its outward appearance, is often the only way to catch a problem early.

Yes. Mass gravity walls rely on weight and thickness, so our survey focuses on identifying voiding or thinning that could compromise that mass. Reinforced concrete walls depend on the condition of internal steel, so mapping reinforcement position, cover depth and any signs of corrosion becomes the priority. Gabion and crib walls behave differently again, with displacement or fill loss being the main risk rather than internal voiding. Because each wall type fails differently, we tailor our survey approach to the construction method rather than applying one standard process regardless of wall type.

Yes. On a reinforced concrete retaining wall, GPR can map the position and approximate depth of internal reinforcement, in a similar way to a ferro scan on a slab or column. This is interpreted alongside the wall’s likely loading and drainage conditions, since reinforcement position on its own doesn’t tell the full story, how it relates to moisture exposure and structural loading matters just as much. This gives a clearer picture of whether reinforcement is positioned as originally designed, or whether corrosion or displacement may be reducing the wall’s structural capacity over time.

Voids within a retaining wall can form for several reasons, including poor original construction, water washing out fine material over time, or gradual deterioration of the wall material itself. In mass gravity walls particularly, voiding reduces the effective thickness and weight the wall relies on to resist pressure from the retained ground, directly affecting its ability to do its job. Because voiding develops from within and isn’t visible from the wall face, it often isn’t caught until a GPR survey is carried out or until the wall has already begun to show external signs of distress.

Our surveyors scan the wall systematically using Ground Penetrating Radar, recording variations in the signal as it passes through the structure. Depending on the wall type, this identifies internal voids, delamination, moisture ingress, or the position of reinforcement, alongside a measurement of wall thickness across the surveyed area. The process is non-intrusive, requiring no drilling or coring into the wall, and can typically be carried out without disrupting any ongoing use of the site or structure, giving you accurate internal condition data without adding delay or damage to the wall itself.

You’ll receive a report and CAD drawing showing wall thickness, any voids or defects identified, and, where reinforcement is present, its approximate position and depth. Rather than a simple pass or fail summary, findings are presented so a structural engineer can properly assess the wall’s remaining condition against its original design intent. This helps inform the right next step, whether that’s ongoing monitoring, a targeted repair, or more significant remedial work, giving you an evidence-based route to a decision rather than working from visual inspection alone.

Yes. Subvision Surveys carries out retaining wall surveys alongside our wider GPR and sub-surface voiding detection services. If a survey identifies wider ground movement, drainage issues or voiding beyond the wall itself, we’re equipped to investigate that as part of the same visit rather than referring you to a separate provider. This is particularly useful where a retaining wall issue turns out to be connected to a broader site condition, giving you a fuller picture of what’s actually causing the problem rather than treating the wall in isolation from the ground around it.

Have Any Questions?

If you have any questions regarding our services feel free to contact the Subvision team.