Seven months after the first historical journey, the second segment of Pennsylvania’s Braddock Dam made an identical 27.5-mi. (44 km) trip up the Ohio and Monongahela rivers.
On Feb. 27, the 9,600-ton (8,640 t) block of floating concrete was pushed by two towboats from the fabrication site in Leetsdale to an outfitting pier at Duquesne. According to the U.S. Army Corps of Engineers (USACE), the second segment is the smaller of the two, measuring 265-ft. (80.7 m) long and 104-ft. (31.7 m) wide. The first section, which traveled the rivers last July, measured 333 ft. by 104 ft. (101.4 by 31.2 m) and weighed 11,600 tons (10,440 t).
According to Project Manager Dennis Olson, each segment was built from 438 precast concrete panels, some weighing as much as 60 tons (54 t).
The dam segment was built by Jones-Traylor Brothers Joint Venture, formed by A. Jones Construction Company, Charlotte, NC, and Traylor Brothers Inc., Evansville, IN. Construction workers were assisted in the move by crews of the motor vessels Joe T. and A.A. Vestal. While the dam was in transit, all waterborne travel was restricted to establish a safety area.
One difference between the second move and the first was the number of observers. Because of security restrictions imposed after the Sept. 11 terrorist attacks, no public viewing was allowed from the USACE’s lock facilities along the way. However, viewing was still allowed at public areas, such as bridges, public wharfs and Point State Park.
Segment No. 2 will remain at the outfitting dock until May 2002, when it will continue the journey to Braddock.
Segment No. 1 Update
The first segment of the dam reached its final destination late last year. On Dec. 5, it was towed downriver 1.5 mi. (2.4 km) from Duquesne to Braddock to be maneuvered into position on its foundation. The 48-hour project required closing the Monogahela River.
According to the USACE, the segment was outfitted with positioning winches and other equipment at the Outfitting Dock in Duquesne. Mooring lines also were connected to fixed anchor piles at various positions in the river near the final set-down location.
While crews from J.A. Jones and Traylor Brothers were positioning the structure over its grid, its location was surveyed extensively, enabling them to position the segment to a tolerance of plus or minus 2 in. (5 cm).
The next step was to slowly fill 30 ballast tanks with enough water to sink the section onto six 6.5-ft. (1.9 m) caissons at the bottom of the river. Horn guides, mooring lines and land-based survey controls were used for guidance, and hydraulic rams were used for precise positioning. Finally, the piece was leveled and grouted into place on the foundation. Vertical and horizontal alignment of the segment was held within 1 in. (2.5 cm) of the specified design values.
The construction of the Braddock Dam is just one phase of a $705-million Monongahela River Project designed to make it “one of the most efficient waterways in the world.” Final completion of the entire project is set for FY 2008.
The $108-million Braddock Dam phase began in August 1999 and will be completed in December 2003. The project utilizes innovative “in-the-wet” construction techniques in order to improve quality and save both time and money. It is estimated that construction time will be reduced by one year, and cost savings will be between $5 million and $15 million.
The decision to use in-the-wet construction was made in July 1997, and innovative design and acquisition processes were required to meet the specific challenges. To aid in understanding of the technology, the USACE contracted Cartesian FX to produce two 3-D digitally animated videos. One of the videos was distributed to more than 300 contractors as part of the Request for Proposal package. The contract was awarded to the Joint Venture in July 1999.
Olson reported that approximately 220 employees are assigned to the Braddock Dam job. Approximately 390,000 cu. yds. (296,400 cu m) of dirt was removed for the river excavation phase. The project will use 89 78-in. (198.1 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. (4.3 million kg) of reinforcing steel.
Major subcontractors for the assignment include Wellington Power Corporation, Pittsburgh, electrical; IHP Industrial Inc., St. Joseph, MO, mechanical; and Luhr Brothers Inc., Columbia, IL, excavation. Bergmann Associates was the lead design architect/engineering firm, and subconsultants were Ben C. Gerwick and D’Appolonia.
The equipment list for Jones-Traylor includes a Vince Hagan Company HT10470 concrete central mix plant with dual 4.5-cu.-yd. (3.4 cu m) mixers, a Grove RT 750 hydraulic crane, an ICE 44-50 vibratory pile hammer, an NLB 1012 D water blaster, and a Volvo L 150C rubber-tired front-end loader. In addition, Traylor Brothers owns three American 9310 crawler cranes and a Manitowoc 3900 crawler crane, and J.A. Jones has two Manitowoc 4100 crawler cranes.
Olson noted that equipment assets owned by the Joint Venture total approximately $4.1 million, and additional equipment rental costs total nearly $200,000 per month.