Abstract: A machine for making underground excavations by compacting soil comprises an eccentric shaft having journals on which there are mounted for a free rotation in a sequence, beginning from the front end, a conical member and tapered rolls forming in combination a conically expanding body. The eccentric shaft is coupled to a drive for rotation. The conical member has a through longitudinal diffuser passage, and the eccentric shaft also has a through longitudinal diffuser passage of a cross-sectional area enlarging in the direction away from the face of the excavation being made. The cross-sectional area of the passage of the conical member is smaller than the smallest cross-sectional area of the passage of the eccentric shaft by an amount such that the inside cross-sectional area of the passage of the conical member is substantially within the limits of the inside cross-sectional area of the passage of the eccentric shaft.