Application Guide
Geophysical Equipment for Cavity & Sinkhole Detection
Natural karst, old mine workings and dissolution features threaten foundations, roads and railways. Geophysics locates voids before they collapse.
A void is a strong physical contrast: missing mass, very high (air-filled) or low (water- or clay-filled) resistivity, and a strong radar reflector. No single method is reliable in all conditions, so cavity investigations normally combine a primary method with a second one to confirm anomalies before drilling.
Microgravity is the classic method because it measures missing mass directly and is unaffected by electrical properties, but it is slow and needs careful terrain and building corrections.
Methods Compared
| Method | Detects | Typical Depth | Limitations |
|---|---|---|---|
| Microgravity | Air- or water-filled voids, mine workings, low-density zones | Depends on void size — detectability falls with depth | Slow; needs precise levelling and terrain corrections |
| Electrical resistivity tomography | Air-filled (resistive) or clay-filled (conductive) voids, karst | Tens of metres | Resolution decreases with depth; urban access can be difficult |
| Low-frequency GPR | Shallow voids, collapse zones, subsidence | Typically up to several metres in resistive ground | Little penetration in clay |
| Seismic (refraction, MASW) | Weak zones, rockhead, loosened ground | Tens of metres | Indirect detection of voids; noisy sites are challenging |
Depths are typical field values — actual performance depends on ground conditions, target size and survey design.
Infrastructure and urban sites
Roads, railways and urban plots add access limits, buried services and vibration noise. Microgravity copes well with electrical noise; GPR is quick on paved surfaces; ERT can be run along verges or in 3D grids. Survey design starts from the expected void size and depth, which determines whether a feature is detectable at all.
Recommended Instruments
A selection from our catalog. We source many more models — tell us what you need.
Which Condition Tier?
Gravimeters hold their value and are frequently supplied Absolute Certified with drift and calibration checks. Earlier-generation gravimeters such as the CG-5 are a cost-effective Refurbished route into microgravity.
See the condition tier guide for what New, Refurbished, Absolute Certified and Surplus each include, or the industries overview for related sectors.
Frequently Asked Questions
What is the best method to detect underground cavities?
Microgravity is the most direct, as it measures the missing mass of a void. ERT and GPR are commonly used alongside it, and anomalies are always confirmed by drilling or probing.
How large a void can geophysics detect?
As a rule of thumb, a void becomes difficult to detect when its depth exceeds about two to three times its diameter, though this varies with method and site noise.
Can GPR find sinkholes under roads?
GPR is effective at detecting shallow voids and loosened ground beneath pavements, especially with low-frequency antennas in sandy or rocky ground.
Other Applications
Utility Locating & Mapping
Ground penetrating radar and electromagnetic (EM) instruments find buried pipes, cables…
UXO Detection
Unexploded ordnance surveys rely on magnetometry and time-domain electromagnetics to find…
Archaeological Prospection
Geophysics lets archaeologists map buried ditches, walls, kilns and graves across whole…
Groundwater & Aquifer Characterisation
Electrical and electromagnetic methods map aquifers, clay barriers, bedrock and saltwater…
Concrete Scanning & Structural NDT
Concrete-scanning GPR locates rebar, post-tension cables, conduits and voids before…
Agricultural Soil Mapping
Electromagnetic conductivity meters map soil variability across whole fields in a single…
Mineral Exploration
Mineral exploration geophysics narrows search areas and defines drill targets — magnetics…
Seismic Site Characterisation
Seismic methods measure the stiffness of the ground directly — depth to bedrock,…