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.

Cavidades Tomografia elèctrica
Cavidades georradar

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.