Near surface geophysical methods have been widely used in geotechnical applications over the last two decades. This is due to the important geotechnical information these methods can provide, regarding the boundaries between geological formations, differences in the rock/soil water saturation, the presence of cavities, faults and the depth of bed rock.
A variety of surface geophysical methods can be used for detecting and delineating of subsurface cavity. The selection of the suitable surface geophysical method depends on the site conditions and a physical property contrast existing between the desired target and the surrounding soil and rock.
The Multi-channel Analysis of Surface Waves (MASW-2D) method in particular has been effectively used in bedrock investigations, soil and rock characterization, as well as in imaging voids and weak zones in rocks due to its low cost and high resolution results .
Electrical resistivity tomography (ERT) is a geophysical method used to image the subsurface using differences in measured electrical resistivity at the surface.