Abstract: A method and a device for obtaining a water-tight shield in a soil apt to being disintegrated by liquid jets, by driving a tool into the soil and filling the furrow left by the tool while it is taken off, by a settable mortar, the operation being repeated step by step so that the tool every time encroaches upon the shield portion obtained during the preceding operation. The tool is driven into the soil through the injection of a settable grout used for disintegrating the soil, which supports the walls of the excavation and is mixed with the disintegrated soil so as to provide a mortar which after setting will form the impervious shield, the injection of grout being carried on during taking off of the tool.