Utilizing HYSPAN™ precast rigid frame sections with a unique joint design, the single lane road under U.S. 460 was reconstructed into a two lane road after the metal plate arch failed.
Permatile teams engineered, precast, and transported the 114 rigid frame sections to the project site for installation by the contractor. A second single-lane tunnel was built under the four lane U.S. 460 simultaneously, to replace a failing metal plate arch.
Started in mid-summer 1994, the underpasses were completed in late August. Local highways and a pedestrian walkway occupy the HY-SPAN SUPERBOXES. Both structures have 17 foot rises, average lengths of 134 feet, and respective spans of 30 feet and 24 feet. Advantages of the HY-SPAN SUPERBOXES include the speed of installation and the ability to spread the load of the structure over substantial area, allowing low strength soil to be built on.
The Superbox design was chosen because of the questionable foundation conditions under the roadway and the superior bearing capability of the Superbox