19 are molded these forms not shown include a semi cylindrical shape on one side for molding the portion of the caissons 35 37 that projects out of the back of the retaining wall at the top of these forms the studs or anchor bolts 82a d are positioned by wire retainers or the like concrete is then poured into the breast wall forms and allowed to harden in the final steps of the method the sound wall 31 is assembled over the top ends of the caissons 35 by first installing the post assemblies 63 onto the studs or bolts 82a d via nuts 83a d and then sliding wall panels 65 between opposing flanges 72a b of the i beams 70 of the post assemblies 63 as shown in fig9 to expeditiously remove the slack between the side edges of the panels 65 and the flanges 72a b of the i beams 70 wedging members 67 are inserted into the complementary shaped recesses 124 present in the corners of the wall panels 65 in the manner described in u s pat no 5 392 572 the entire specification of which is incorporated herein by reference as the panels 65 are slid between the flanges 72a b of the i beams 70 the weight of the panels cooperates with the inclined surfaces of the wedging members 67 to firmly press and retain the front side edges of the panels 65 against these flanges thus obviating the need for bolt and angle type slack removers while this invention.