Almost 3,000 lineal feet of precast tunnel runs beneath the Boeing Company's 747 airplane assembly plants in Everett, Washington. This tunnel is used for pedestrian traffic and utility distribution. The design uses a precast concrete arch comprising two quarter-circle segments bearing on a cast-in-place floor slab. A cast-in-place closure strip at the top of the arch joins the precast elements together, eliminating the need for connection hardware and field welding.
