24” Bottom Block Height 18” x Width 48” x Depth 24” The Big Block 24″ Bottom Block is used as the base block or first course block in retaining wall construction. The 24″ bottom block is flat on the bottom and sits upon the crushed gravel or AB3 leveling pad. Click here for a PDF version. Click here for a DWF version. Click here for a DWG version. Return to "Big Block Retaining Wall Engineering" page.