above two segments are attached together to form a section the section is either lifted onto or dragged over the installation form to take on the desired arched form of arch shaped forming members 36 37 shown in fig6 and 7 spacers are then inserted in the gaps with specially shaped spacers provided as required such predetermined shapes being established by the gaps that take shape when the wall section is placed on the forming members cable 17 is then secured in place by using fastener plates 51 on appropriate blocks the spacer not shown for the gap in which fastener 51 is placed will necessarily be inserted after the plate is in place after the cable is snugly secured in its final position by use of turnbuckle 18 installation form 35 is dropped to the phantom position shown in fig6 and the completed section is suspended on lift arm 50 crane assembly 46 then transports the completed section from its position above the installation form to the position shown in phantom at which time another section can be formed in a like manner when the next formed section is completed it is moved to a position adjacent the previously formed section whereupon the two section are secured to.