Geology and detection of underground cavities
The detection of underground cavities using geophysics is part of a risk reduction process, thus reviewing the integrity of the terrain before moving heavy equipment overhead such as cranes. It is also used to delimit the extent of possible underground voids and subsidence for repair planning.
When we need geophysics
The georadar makes it possible to study the first meters of geological layers and determine the location and extent of underground cavities, sinkholes and subsidence. The use of the georadar is recommended at the slightest sign of subsidence, such as potholes in clay and cracks in harder materials. However, in cases where the surface is firm and supports its own weight, the material below may sink until a significant void has developed under the surface layer with no visible warning signs. The surface can break when heavy loads are applied or, if the vacuum reaches a size where it can no longer support its own weight, collapse on its own.
Causes of underground cavities
- Socavon (the causes of which can be geological or man-made, such as broken water pipes, old sewers, buried basements, and compromised disused mine shafts).
- Washing of materials due to the movement of groundwater that carries some material (typical in coastal walks and parking lots, ports and retaining walls).
- Natural subsidence in which the ground itself moves and settles over time.
What equipment do we use
The combination of resistive electrical tomography (ERT) and georadar allows the detection of underground cavities with higher quality. Georadar data accurately determines the size of an anomaly in a homogeneous, low-conductivity medium, and ERT helps determine areas of high resistivity at the cavity location. If we combine these two geophysical methods, using the depth of the interfaces in the radargrams as information, a priori to restrict the inversion of the electrical resistivity models, we obtain resistivity models that are better adjusted to reality.
Example of Detection of Cavities with Electrical Tomography
Electrical resistivity tomography is an effective tool for identifying cavities in the subsurface. In this case study, areas with high resistivity were detected, associated with the presence of air in underground cavities.
This method enabled precise mapping of the cavities, alerting the client to potential risks and providing critical information for their project. Electrical tomography is ideal for addressing complex geological challenges and ensuring success in engineering and construction projects.
These electrical tomography studies are also useful for identifying geological units in the subsurface, allowing for the precise definition of contacts and boundaries between different geological formations.
