A method and apparatus is provided for producing subterranean walls comprised of granular material. The apparatus comprises a beam for making insertions into and extractions out of the ground to form a series of voids therein. The beam includes a hollow interior portion which receives a supply of granular material. The beam also has a plurality of outwardly projecting spurs on the outer faces thereof for scarfing the sidewalls of the void as the beam is extracted. The apparatus also includes a disposable shoe which is removably attached to the open bottom portion of the beam to prevent earthen material from entering the hollow interior portion of the beam as the beam is inserted into the ground. An actuating mechanism detaches the shoe from the open bottom portion of the beam after the beam has been inserted into the ground so that granular material is released into the void as the beam is extracted therefrom. The method comprises the following steps: suspending the beam above the ground; removably installing a disposable shoe onto the open bottom portion of the beam; inserting the beam and the removably installed shoe into the ground to form a void therein; delivering granular material to the hollow interior portion of the beam; detaching the shoe from the bottom portion of the beam; and extracting the beam from the ground while the spurs cut vertical channels in the sidewalls of the void and granular material flows through the open bottom portion thereof to fill the void with granular material.