To complete an underground section of roadway, an Arizona contractor had to develop equipment for placing 7-ton precast concrete panels in tight quarters. The contractor, M. M. Sundt Construction Co., was to provide the lighting, signing, pavement markings, and electrical and mechanical systems. The only unusual part of the job was that the mechanical systems involved ventilation because the road is underground. The Arizona Department of Transportation designers had called for ventilation chambers shaped by precast panels. Sundt project managers had to devise a method for casting and erecting those panels within a closed space, given only 3 inches of clearance at the top and bottom. They came up with the idea of modifying a wheel loader that had large enough tires and the needed lift capacity. To attach the panel to the strongback, the design team used formed conical chambers in the panel and mated them with expandable, reusable bolts. This was the typical construction sequence:
- Attach panel.
- Break bond and lift clear of slab.
- Strip bond breaker and clean vertical edges.
- Lift and rotate to vertical position.
- Move forward to position adjoining previously placed panel.
- Move into final position.
- Hold panel in position until fastened.
- Release panel.
- Back loader away and repeat cycle.