Ground Risk · Service
Void, Cavity and Underground Tank Detection
Finding the empty space beneath a road, apron, floor or embankment before it announces itself — loss-of-ground washouts, settled backfill, karst cavities and abandoned structures located from the surface.
Owned fleet only: 1.5 lakh+ km delivered, 100 km a day peak output and a best month of 700 KM in 30 days. A ₹1,00,000 per-project minimum applies outside Delhi NCR to cover rig and crew movement from Faridabad. NCR sites have no such floor.
Overview
Subsidence is the symptom, not the event
By the time a surface dips, cracks or collapses, the ground has usually been failing quietly for months. A leaking sewer washes fines out of the surrounding soil; a poorly compacted service trench settles under traffic; groundwater dissolves a path through soluble rock. Radar reads the boundary between solid ground and the loosened or empty zone above it, so the problem is found while it is still an inspection item rather than an incident.
- Voids, washouts and loosened backfill
- Abandoned tanks, wells and old structures
- Continuous coverage, not spot boreholes
- Findings ranked so remediation is targeted
What Causes Them
Where the empty space comes from
Leaking Drainage
A cracked sewer or storm line steadily washing soil fines away into the pipe.
Leaking Drainage
A cracked sewer or storm line steadily washing soil fines away into the pipe.
Poor Trench Reinstatement
Backfill placed without proper compaction, settling under repeated axle loading.
Poor Trench Reinstatement
Backfill placed without proper compaction, settling under repeated axle loading.
Water Movement
Groundwater or surface ingress carrying material out from beneath a slab or embankment.
Water Movement
Groundwater or surface ingress carrying material out from beneath a slab or embankment.
Dissolution Features
Natural cavities forming in limestone and other soluble ground over long periods.
Dissolution Features
Natural cavities forming in limestone and other soluble ground over long periods.
Buried Structures
Forgotten septic tanks, wells, basements and culverts left in place and later covered.
Buried Structures
Forgotten septic tanks, wells, basements and culverts left in place and later covered.
Made Ground
Old fill and demolition rubble consolidating unevenly beneath a newer surface.
Made Ground
Old fill and demolition rubble consolidating unevenly beneath a newer surface.
Where We Are Called
Sites that justify a void survey
City carriageways where a depression has appeared and the municipal engineer needs to know its extent before deciding between a patch and a proper excavation. Airport aprons and taxiways, where a void beneath a slab is a safety matter and closing a stand for exploratory digging is expensive in itself.
Industrial floors carrying heavy plant, where settlement under a machine base is both a production and a structural problem. Railway formations and approach embankments, where loss of support is dangerous and inspection windows are short. Dam toes, canal banks and flood embankments, where seepage paths and internal erosion are the concern rather than a surface hole.
And increasingly, pre-purchase and pre-development due diligence: a plot with a history of industrial use, unrecorded fill or old structures, surveyed before anyone commits to a foundation design. In every case the value is the same — continuous coverage that tells you where to dig, instead of boreholes that tell you only about the points you happened to choose.
Method
Survey approach and reporting
| Primary method | Ground Penetrating Radar at lower antenna frequencies to favour depth over fine resolution |
|---|---|
| Antenna frequency | Typically 100–400 MHz depending on target size and required depth of investigation |
| Survey pattern | Close-spaced orthogonal grid across the area of concern, extended beyond the visible symptom |
| What is interpreted | Loss of signal continuity, strong reflection at an air or water interface, and disturbance of natural layering |
| Anomaly classification | Findings graded by confidence and apparent significance so remediation can be prioritised rather than blanket-applied |
| Confirmation | Borehole, probe or camera survey recommended at selected anomalies where the client needs certainty before design |
| Deliverables | Anomaly plan with grid reference and estimated depth, radargram extracts for key findings, and an interpretation report |
| Repeat monitoring | Baseline and follow-up surveys on the same grid where a feature is being watched over time |
Radar shows a contrast, not a certificate. An anomaly consistent with a void may be a genuine cavity, a saturated zone, a change in fill material or a buried object — and depth of investigation falls sharply in clay-rich or waterlogged ground. We report what the data supports, grade our confidence honestly, and recommend intrusive confirmation where a decision carries real consequence.
Commercials
What the survey is priced against
Void work is quoted by area and by grid density, and the second one is the variable most clients do not expect. Detecting a large cavity needs only a coarse grid; detecting a small washout at the same depth needs lines close enough that the feature cannot sit between them. Tell us the smallest thing you need to find and the price becomes explainable.
Depth of interest follows: shallow slab-support checks are quick, while investigating several metres down means lower frequencies, slower progress and more interpretation. Surface type matters too — smooth concrete and asphalt give clean data, while broken ground, loose gravel and vegetation degrade it and slow the crew.
Access and operating conditions complete the picture. Live carriageways, airport airside areas and operating plant all require escorts, permits or night windows. Where a client wants confirmation boreholes, those are a separate civil activity priced on its own. See our cost guide for how radar work is quoted generally.
Assurance
How an anomaly becomes a finding
Nothing is called a void on the strength of a single line. Every candidate anomaly must appear on crossing traverses before it enters the report, which is why grid spacing is agreed in writing before mobilisation rather than decided in the field. Interpretation is done against a site-calibrated velocity rather than a textbook default, so quoted depths mean something. Each finding carries a confidence grade and a plain statement of what else could produce the same response, because an engineer deciding whether to close a runway or dig up a road deserves the alternative explanation as well as ours. Where features are being monitored over time, repeat surveys are run on the identical grid with the same equipment settings so genuine change is distinguishable from survey variation. Work is delivered under our ISO 9001:2015 quality system with raw data retained for independent review.
What our own fleet has actually delivered
FAQ
Void detection — common questions
An air-filled space produces a strong, distinctive reflection because air and soil are so different electrically. Water-filled and partially collapsed features are subtler but still detectable. What radar cannot do is confirm the finding physically — that needs a probe or borehole.
It depends far more on the soil than on the equipment. Dry sand, gravel and rock allow several metres; clay, black cotton soil and saturated ground can cut usable depth to a fraction of that. We assess the ground before committing to a depth of investigation.
If you want to know whether the cause extends beyond the visible damage, yes. Surveying the surrounding area regularly shows the affected zone is larger than the symptom — which changes the repair scope and stops the same failure returning next season.
They answer different questions. Boreholes give certainty at a point; radar gives continuous coverage across an area. The efficient approach is radar first to find where the problems are, then a small number of boreholes placed on those anomalies rather than on a blind grid.
Usually a lane or a working section is enough, with traffic management around it. On airside and operating industrial areas we work to your permit system and, where required, in night windows.
Grouting and structural remediation are specialist trades we do not claim. Our role is to define the problem accurately enough that a remediation contractor can price and target it properly, rather than treating a whole area on suspicion.
We have pushed to 100 km a day on unobstructed corridors, using night working and company-owned radar systems. A single 30-day programme has delivered 700 KM, which remains our record. In total we have completed more than 1.5 lakh km of GPR survey. Actual pace on any given site is governed by utility density, access windows and the output format required.
Ground settling where it should not be?
Send us the location, the surface type and what you have already seen — we will propose a grid and a depth of investigation that matches the risk.
Request a Void SurveyVoid and cavity detection — method, output and detailed questions
Mezux Touch investigates suspected voids beneath roads, slabs and paved areas, which is a different survey question from finding a pipe. A void is not an object; it is an absence, detected by the way radar responds to the boundary between soil and air or water. That makes grid density the governing variable, because a cavity smaller than the line spacing is stepped over entirely. Most voids we find are caused by water: a leaking drain washing fines out of the surrounding soil, or repeated saturation moving material until the ground above loses support.
How the work is run
Line spacing is set against the smallest cavity that would matter to the client, not against a standard grid, and it is usually far tighter than a utility survey would need. Passes are run in both directions because a void's response varies with the angle of approach. Where a suspected void is found we scan outward from it to establish its extent rather than just its centre, since the client's real question is how much ground has lost support. Where a finding is ambiguous we say so and recommend a probe rather than reporting a cavity that may be a soft zone.
What you receive
A plan showing suspected voids with their extent rather than a single point, graded by confidence and by how consistently they returned across passes. Depth to the top of each anomaly. A signed report stating the grid density used, because a void survey's value depends entirely on that figure and a client comparing quotations deserves to see it. Where the likely cause is identified, such as a drain running through or beside the anomaly, that is set out so the remedy addresses the cause rather than only the symptom. Recommendations for probe or intrusive confirmation where the response was ambiguous.
Beyond the basics
How small a void can you find? That depends entirely on line spacing, which is why we state it. A cavity smaller than the grid is stepped over, so the grid is set against what would matter to you.
Can you tell a void from a soft zone? Often, from the sharpness of the response, but not always. Where it is ambiguous we say so and recommend a probe rather than committing to a finding.
What usually causes the voids you find? Water, in almost every case — a leaking drain washing out fines, or repeated saturation moving material until support is lost above.
Do you report the extent or just the location? Extent, because the client's real question is how much ground has lost support. We scan outward from a find rather than stopping at its centre.
Is this the same as a utility survey? No, and the two should not be priced alike. Void work needs far tighter grids, which means slower coverage and a different rate.
Terms used on this page
Loss of fines — the washing out of small soil particles by water movement, which leaves a cavity behind. Grid density — how closely survey lines are spaced, the single figure that determines what size of void can be found. Soft zone — weakened ground that is not yet an open cavity, which can read similarly to a void. Extent — the plan area over which support has been lost, as distinct from the point where a void was first detected. Probe — a slim intrusive confirmation used to verify whether an anomaly is a genuine cavity.
