The purpose of the dilatometer Marchetti test is the designation of the strength and deformation parameters of the soil in situ by the deformation of a thin circular steel membrane, mounted in the plane of one side of a steel blade-shaped probe, inserted vertically into the soil.

The dilatometer is pressed from the terrain surface and the measurements can be performed at different range, for example every 20 cm. Pressure measurement is performed at every depth at two positions of the membrane: first, when it is in one plane with the blade, the pressure required to initiate movements of the membrane is measured (measurement A), then the pressure after its pulling out by 1.1 mm towards the soil is measured (measurement B). In addition, the pressure after the membrane's return to the starting position can be measured as well (measurement C).

The dilatometric tests are, most commonly, used for low-bearing soil investigations, in particular the organic ones. The SDMT test is additionally extended by data from the seismic module.