McLean County, Kentucky
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State of Kentucky
Kentucky Transportation Cabinet (KYTC)
Over 68,000 bridges across the U.S. are classified as scour critical by Federal Highway Administration (FHWA) standards. In 1999 the Kentucky Transportation Cabinet (KYTC) proposed a series of bridge scour contacts to protect 17 scour critical bridges in six counties.
The scope of the McLean County bridge required the use of Armortec A-Jacks concrete armor units placed within an engineered matrix around the piers on both sides of the creek crossing. A total of 900 A-Jacks units were placed after excavation, providing a coffer dam throughout the installation process. Scouring depths were determined and scour contraction was identified. This justified the placement of A-Jacks 8-ft. upstream of the piers and tied in A-Jacks across the full width of the streambed under the bridge.
The installation lasted only two days. Five laborers and two pieces of excavation equipment were used to clear and install the A-Jacks 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 and are defined in HEC-23 as one of six acceptable scour countermeasures endorsed by the FHWA.
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