Abstract: A method is provided for constructing an underground wall in a trench, include using multiple chains on an endless chain cutter and individually controlling the speed and/or direction of the chains, various configurations of cutter bits and agitator bars on the chains, a technique for assembling the endless chain cutter in a horizontal position outside of a starter trench, then erecting the endless chain cutter to a vertical position in the starter trench. A guide frame straddles the starter trench. The endless chain cutter is repeatedly moved within the guide frame, then the guide frame is re-positioned until the entire length of the trench has been excavated. A central portion of the trench may be cut deeper than outer portions to create interlocking joints between adjacent wall sections and added stability for the resulting wall. Side gap barriers seal gaps between the sides of the endless chain cutter and side walls of the trench.