Over 68,000 bridges across the U.S. are classified as scour critical by FHWA standards. In 1999, the Kentucky Transportation Cabinet (KYTC), through the efforts of Fuller, Mossbarger, Scott & Mat Engineers and funding from the FHWA, proposed a series of bridge scour contracts to protect 17 scour critical bridges in six counties.
The scope of the Graves County creek project required the placement of A-Jacks concrete armor units within an engineered matrix around the piers on both sides of the creek crossing. A total of 5,050 hard armor units were placed after excavation providing a coffer dam throughout the installation process. Scour depths were determined and scour contraction was accounted for, which justified placing A-Jacks eight feet upstream of the piers and tied in A-Jacks across the full width of the streambed under the bridge.
The installation lasted two days. Six laborers and two pieces of excavation equipment were used to clear and prepare the site as well as backfill the units at the end of construction. A-Jacks are recognized as a permanent high performance and cost effective scour countermeasure alternative to riprap. They are one of six acceptable scour countermeasures endorsed by the FHWA.
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