Abstract: A structure for forming a vertically orientated wall comprises a flexible front panel having a longitudinal axis, a transverse axis and substantially continuous front surface; a flexible rear panel positioned rearwardly and parallel to the front panel; and a plurality of cross members connecting the front and rear panels. The front and rear panels define an upwardly opening cavity therebetween for accepting filler material, such as concrete therein. The rear panel includes at least one longitudinally disposed laterally deformable portion, such as a channel or zig zag pattern, which allows for the associated expanding and contracting of the rear panel during adjusting of the arcuate configuration of the wall structure.