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Allegheny Lock 6 Emergency Erosion Repair

Location: Armstrong County, PA
Owner: US Army Corps of Engineers, Pittsburgh District
General Contractor: Brayman Construction Corp.
Value: $2.9 Million
Date Complete: September 2009

This project included emergency erosion repair as identified during a periodic survey. The underwater inspection identified an area of erosion along an approximate 200 ft section of the dam that extended approximately 29 ft under the structure directly adjacent to an existing hydroelectric facility.

The repair work consisted of filling the existing voids beneath the structure and installing additional scour protection downstream of the dam to provide against future scouring. Sheetpiles were used to seal off the downstream section of the dam and open void. Tremie grout was placed between the sheets and the dam to one foot below the base of the dam. With the sheets in place and bulk grout injected along the toe of the dam, a series of 10 in diameter grout injection holes were drilled through the apron of the dam to facilitate the installation of additional grout to fill any remaining voids. In all, over 800 cy of grout was placed to fill the voids beneath the dam.

During repair operations, work was periodically halted due to high water fluctuations of the river. All critical dam repairs were substantially completed by mid-January 2009. The downstream scour protection work consisted of rip rap placement, derrick stone placement, along with the placement of a high strength concrete cap between the top of the installed sheet pile wall and the apron of the dam.  These renovations were accomplished once river conditions returned to manageable levels and offered a safer working environment.