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. The beam includes a top portion, an open bottom portion, and a hollow interior portion therebetween which receives a supply of granular material. In usage, the beam is inserted into the ground to form a void therein. The apparatus also includes a disposable shoe which is removably attached to the open bottom portion of the beam. In usage, the shoe prevents earthen material from entering the hollow interior portion of the beam as the beam is inserted into the ground. The apparatus further includes an actuating mechanism which 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 granular material flows through the open bottom portion thereof to fill the void with granular material.