PURPOSE: To improve the transmission of stress in wall body and the reach of concrete by a method in which an angle iron bar section and a horizontal iron bar section are provided on both sides of a partition steel plate, and vertical iron bars are welded to the up- and downside of the horizontal iron bars.

CONSTITUTION: A steel joint 1 consists of a partition steel plate 3 and large numbers of folded type horizontal iron bars 9, and each folded type horizontal iron bar 9 consists of an angle iron bar section 9A and paired horizontal iron bar sections 9B. For each folded type horizontal iron bar 9, the angle iron bar section 9A and the horizontal iron bar section 9B are provided on both sides of the partition steel plate 3 and pierced each othr through the through holes 10 of the steel plate 3. In the adjacent folded type horizontal iron bars 9, the top of the angle iron bar section 9A of one iron bar 9 is welded with the horizontal iron bar section 9B of the other iron bar 9. Reinforcing vertical iron bars 8 are welded to the up-and downsides of the horizontal iron bar section 9A, and a preceding wall body 2A and a following wall body 2B are connected with the steel joint 1 to build up a continuous underground wall.