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Tilt-Up Solution for Lock and Dam Project

By: Wendy Ward

When the 100-year old Braddock Locks and Dam on the Monongahela River south of Pittsburgh, Pa. needed replaced, Tilt-Up construction played an important role in the equation. An in-the-wet method
was chosen over the typical in-the-dry method, which restricts the 22 million tons of annual commerce on the river for long periods of time. The goal of the project was to replace several locks and dams on the Monongahela River to increase traffic flow and service to Pittsburgh.

The in-the-wet method meant the two large sections of the dam had to be constructed up-river. Once completed, the sections floated down the river to their resting place. The two sections, 333 feet and 265 feet long and 110 feet at the widest spot, were built out of site-cast panels (438 of them). Since the panels had to be temporarily braced to the ground and each other, they were considered a Tilt-Up structure measuring up to 50 feet tall.

Section one weighed nearly 17,000 tons and was floated down the river in July of 2001. Section two, weighing 13,500 tons, was floated in February of 2002. After being sunk into place, these sections made up the bottom third of the lock. The groundbreaking 27.5-mile trek proved to be tricky at times. The trips took almost 15 hours each and were very complicated as they had to travel under bridges and through existing locks and dams. The concrete segments were towed through Dashfields and Emsworth Locks on the Ohio River, nearly filling the lock chambers. The section of concrete, 3,300-horsepower primary tow boat, two assistant tow boats and escort vessels travelled in the heavily used water of the Port of Pittsburgh as thousands of onlookers lined the riverbanks and cheered.

Most of the design and build bids for the project involved the in-the-dry method of river coffer dams, which restricts the river traffic for years. In contrast, the in-the-wet method kept the river open while the structure was being built. The ACOE- Pittsburgh accepted “best value proposals to the government” and the joint venture of JA Jones/Traylor Brothers was selected. Time of schedule, cost and the in-the-wet method offered the best value to the city of Pittsburgh.

The in-the-wet construction project was completed to rave reviews. For the first time in civil engineering history, an inland navigation dam was created using innovative float-in technology, wherein two massive concrete dam segments, fabricated on land, were launched, floated in place and submerged onto a previously constructed large diameter drilled shaft foundation.

Some concerns that were dealt with by using a Tilt-Up design occurred in the construction phase and involved the lifting and bracing of the 438 panels needed for the floating ship. One challenge involved construction of the floating ships that were strong enough to withstand water pressure and able to be maneuvered down the river with the help of tugboats. Another challenge was that the two sections of concrete had to be able to fit through the locks along the way and also had to be able to drift under the many overhead bridges. These concerns were overcome with innovative engineering, which took great consideration with respect to the laws of buoyancy and water displacement.

According to Mike Wolstenholme, National Tilt-Up Sales Manager for Meadow Burke Products, the main lesson learned was that conventional thinking is not always the best solution. Wolstenholme said, “The in-the-wet method using Tilt-Up ’ships’ floated in to place saved time and eliminated river traffic issues.”

The Braddock Locks and Dam were originally built from 1902 to 1906 and the project underwent revisions in 1953 and then replacement in 2004. It is comprised of a 721-foot gated dam, a 110-foot-by-720-foot land side lock, and a 56-foot-by-360-foot river side lock which provide for an 8.7-foot vertical lift. From 2000 to 2005, more than 2,200 recreation vessels, 3,800 commercial tows and 17.8 million tons of cargo passed over the Locks. Cargo consists of coal, petroleum, chemicals, crude materials, manufactured goods, farm products, manufactured machinery and other commodities. The average annual transportation cost savings associated with this facility from 2000 to 2005 is over $124 million. The completion of the project occurred in April of 2004. The project cost was $107.4 million.

The Braddock Dam project incorporates significant new and innovative business practices with respect to design, construction, procurement and contract management that have received notable interest and endorsement. Further, it is yet another example of how site-cast Tilt-Up construction can solve design and construction challenges.

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TILT-UP TODAY, a publication of the Tilt-Up Concrete Association, is THE source for Tilt-Up industry news, market intelligence, business strategies, technical solutions, product information, and other resources for professionals in the Tilt-Up industry. A subscription to TILT-UP TODAY is included in a TCA membership. Subscriptions for potential TCA members are also available. If you would like to receive a complimentary subscription to the publication, please contact the TCA.