History was made in Pennsylvania on July 26 as people gathered along the Ohio and Monongahela (Mon) rivers to see for themselves that concrete really could float. The spectacle was definitely something to see as 22 million lbs. (9.9 million kg) of reinforced concrete slowly made a 27.5-mi. (44 km) journey up the river.
The football-field sized chunk was one of the segments of a new navigation dam under construction near Braddock, PA. The dam project initiates the final phase of a program by the Pittsburgh District, U.S. Army Corps of Engineers (USACE) to modernize the locks and dams on the Monongahela River.
According to the USACE, approximately 44 million tons (3.9 million t) of commerce moves through the Port of Pittsburgh and along the region’s waterways, which include the Allegheny, Monongahela and Ohio rivers. That number is expected to double by the mid-2000s. Approximately half of the commerce must pass through the lower Monongahela River area, which includes Lock 2 near Braddock, Lock 3 near Elizabeth and Lock 4 near Charleroi. These three locks are currently the oldest operating navigation facilities on the Mon River, completed in 1905, 1907 and 1932.
To keep river transport safe and economical, the USACE began the project to replace the fixed-crest dam at Lock and Dam 2 with a gated dam, remove Lock and Dam 3, and construct two new locks at Lock and Dam 4. The new dam at Lock and Dam 2 will control the water level along the river and allow for flood control. The new larger locks at Lock and Dam 4 will accommodate large tows, which currently must lock through in sections. Finally, the elimination of Lock and Dam 3 will remove a major bottleneck. Final completion is scheduled for 2008, and the total estimated cost is $705 million.
According to the USACE, when the Monongahela River Project is completed, “The entire Mon River will be one of the most efficient waterways in the world.”
Lock 2 (Braddock Dam)
The Braddock Dam phase of the Monongahela River Project began in August 1999 and is scheduled for completion in December 2003. The contract amount is approximately $108 million, with funding provided by the government. In addition, the Waterways Industry contributes to the funding on a 50/50 basis via the diesel fuel tax to the Inland Waterways Trust Fund. The project owner is the United States Army Corps of Engineers, and Joint Venture partners are J.A. Jones Construction Company, Charlotte, NC, and Traylor Brothers Inc., Evansville, IN.
“In-the-Wet"
Construction
The Braddock Dam project utilizes innovative “in-the-wet” construction techniques to improve quality and save both time and money. It is the first use of such technology by the Corps, although float-in construction has been successfully used for many years for bridge piers, offshore oil and gas facilities and submerged tube tunnels. Using “in-the-wet” technology is expected to save between $5 and $15 million and reduce the construction time by one year.
The base of the dam was constructed in two large segments at a fabrication site on 30 acres of land at Leetsdale Industrial Park, which is approximately 15 mi. downriver from Pittsburgh.
Project Manager Dennis Olson said, “This is the first time the new in-the-wet construction method has been tried for a navigational dam anywhere in the world. Thus, the challenges have been numerous. The first challenge was to complete construction of the casting/launching basin in a very short time frame. During construction of this site, which is located at Leetsdale, a significant archeological find was made, requiring the Joint Venture to revise the planned site layout,”
Dam Segment No.1 is 333 by 104 ft. (101 by 31.6 m) and weighs approximately 11,000 tons (9,900 t) while Dam Segment No. 2 is 265 by 104 ft. (80.7 by 31.6 m) and weighs approximately 9,000 tons (8,100 t). Olson explained that the dam segment preparation incorporated several different methods of construction. Each segment was assembled from 438 reinforced concrete panels, which were precast in the conventional fashion, and steam curing was used to accelerate concrete cure times. However, erection of the panels was difficult because some of them weighed as much as 60 tons (54 t). The panels were interconnected in a gridlock fashion with a continuous concrete slab underneath, resulting in a boat-like structure with watertight interior cells. These cells and the use of transport bulkheads allow the segments to float because of Archimedes’ Law of Buoyancy, which states, “The upward force on an immersed object is equal to the weight of the displaced fluid.”
Olson said, “The segments are both heavily reinforced and the interior panels heavily braced to accommodate the loads which are imposed on the segments during the immersion process.”
The first Braddock Dam Segment entered the Ohio River from the casting basin in Leetsdale at 7 a.m. on July 26. Nearly 14.5 hours later, it arrived safely at its first destination in Duquesne. The journey moved the segment through Dashields and Emsworth Locks on the Ohio River and Lock 2 on the Monongahela River. Speed was limited to no more than 4 knots, but averaged between 2 and 3 knots.
Currently, the segment is moored at the outfitting pier in Duquesne and is undergoing final construction work. The next step is to tow it to the new Braddock Dam site, where it will be flooded and sunk onto a prepared underwater foundation system of sheet-pile cut-off walls and large diameter drilled shafts. Finally, the segment will be concreted into position. The second segment is scheduled to be launched in early 2002. Once both segments are in place, the remainder of the dam construction will take place above the water.
Olson noted, “While the ’float out’ of the first segment was an important step, it was but the first milestone in the project, with several other major milestones yet to be accomplished. Segment No. 1 is now in the process of being ’outfitted,’ which includes placing more concrete in the segment, plus the addition of a work deck, a ballast system for the immersion process, and the installation of both grout bags and winches for controlling the immersion process. Segment No. 2 is nearing completion, and then it ships to the Braddock site for outfitting once Segment No.1 has been ’set down.’ After immersing the segments, some 50,000 cu. yds. (38,000 cu m) of infill concrete must be placed to provide ballast for the segments.”
For final placement, each segment will be maneuvered downriver by a primary tow and guided by a snubbing tow. At the set-down site, mooring lines will be connected to the winches that are mounted on the segment. The lines will be used for final positioning over the horn guides before the segment is ballasted onto the set-down drilled shafts. Next, the segment will be lowered into position by adding water and using the horn guides, mooring lines and land-based survey control for guidance. Final positioning will require the use of hydraulic rams.
Project Size
According to Olson, there are approximately 220 employees assigned to the Braddock Dam project. Approximately 390,000 cu. yds. (296,400 cu m) of dirt was moved during the river excavation phase. The dam involves 89 78-in. (198.12 cm) diameter drilled shafts, four 160-ton (144 t) tainter gates, eight 40-ton (36 t) maintenance bulkheads, 70,000 cu. yds. (53,200 cu m) of concrete, and approximately 9.5 million lbs. (4.28 million kg) of reinforcing steel.
Equipment and Subcontractors
Olson said, “The equipment fleet is considerable on this project. It includes equipment owned by the Joint Venture, rented from one of the Joint Venture partners, and rented from third party vendors.” Some of the third party vendors include Brayman Construction Company, McDonough Marine, Knickerbocker, Beckwith Machinery, Godwin Pump, Cat One Call Rental, All Crane Rentals, Equipment Corporation of America, WACO Scaffolding, and Symons. Equipment assets owned by the Joint Venture total approximately $4.1 million, while equipment rental costs total nearly $200,000 per month.
Major equipment owned by Jones/Traylor includes a Vince Hagan Company HT10470 concrete central mix plant with dual 4.5-cu.-yd. mixers, a Grove RT 750 hydraulic crane, an ICE 44-50 vibratory pile hammer with caisson beam clamp, an NLB 1012D water blaster and a Volvo L150C rubber-tired front end loader. Traylor Brothers owns three American 9310 crawler cranes and a Manitowoc 3900 crawler crane, and J.A. Jones contributed two Manitowoc 4100 crawler cranes, one of which is a Series 2. In addition, the group is using a 60- by 22-ft. (18.2 by 6.7 m), 800 hp (596 kW) push boat MV “Andrew J” owned by Jay Hall Jr.
Major subcontractors include Wellington Power Corporation, Pittsburgh, electrical; IHP Industrial Inc., St. Joseph, MO, mechanical; and Luhr Brothers Inc., Columbia, IL, excavation.
Olson said, “There are numerous other subcontractors and vendors involved in this project, all of which are important to the successful completion of the project. Unfortunately, it is not possible to mention all of them.”
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