When it is necessary to perform excavations of large diameter to be used as tunnels or shafts, in loose, thickened grounds or even conglomerates, with a strong presence of water that cannot be drained, an effective separation between the groundwater and the soil that will be excavated is realized by freezing techniques.

Horizontal and vertical perforations are realized along the perimeter of the tunnel or shaft, in which are insered some pipes containing a coolant (normally CaCl2 or nitrogen), with temperatures of the order of -45°C/ -120°C to freeze the ground around, forming frozen columns with diameters up to 2.0 mt.

The perforations can be realized using drilling probes, but in the case of tunnels is better to use larger equipment called positioners which permit to realize horizontal holes with height from the level of the wheels up to 10,20 mt, with considerable advantages of continuing the work in steps of 8-9 mt.