The City of Boulder chose cast-in-place concrete for the box culverts carrying Colorado's Goose Creek under the Foothills Parkway. These 7-barrel and 5-barrel culverts, each more than 300 feet long, were built with 5x8-foot barrels.
Anticipating problems at the prebid stage through careful scrutiny of the contract documents can save hassles later and enable the contractor to make a more precise bid as well. The contractor should check the amount allowed for excavation because it may differ from the actual excavation needed on the jobsite. What to do about water flow at the site should also be considered at the prebid stage. Typically box culverts are built in a flood plain and below the water table, resulting in a water problem during construction.
The base slab for the box culvert was made 3 inches wider on each side to provide a base for the heavy crane-handled form panels. Labor saved in form alignment more than offset the cost of the extra concrete. Crane-handled forms were constructed of 3/4-inch overlaid (plastic faced) plywood backed by horizontal 4x4s. A rough-terrain crane picked and set each panel. The basic gang form construction was strong enough to permit use of heavy reusable ties at relatively wide spacing. The top of the culvert box was built as a suspended slab, with deck forms supported on rented horizontal shoring made of telescoping bar joists.