A device and process for sinking vertical wells. A pair of rotary digging heads have horizontal axes mounted on supports for movement of such axes towards and away from each other between a central position close to the axis of a well and a peripheral position adjoining the wall of the well being formed. The different heads are spaced apart so that the horizontal components of the reactions resulting from them cancel each other out. A process for using the device to form a well wherein the heads are initially close together and progressively move apart as the well is formed.