Braddock New Gated Dam on Monongahela River, Allegheny County, PA
Innovative “in the wet” construction began the summer of 2000 for this project, located approximately 11 miles south of Pittsburgh. The original dam was completed in 1906 and was replaced by a gated dam to improve navigation along the lower Monongahela River. The Braddock Locks, located on the Monongahela River, are responsible for transporting 19 million tons of freight per year.
The duration of construction included five winter seasons, with daytime highs between 19 and 25 degrees Fahrenheit and temperatures falling into the low teens to zero at night. High winds often drove wind chills to temperatures below zero. There were ice floes on the river, and at times the river would freeze over entirely. The team continued to work through the winters using crane barges secured with spuds. Deck barges were moored upstream of the crane barges to divert ice floes. Concrete production was maintained by heating the materials and protecting placed concrete from freezing.
Two portions of the dam, consisting of football-field-sized precast hollow-core concrete dam segments, were constructed at an offsite precast yard. The larger of the two sections was 333 feet long, 106 feet wide and 40 feet high.
Precast panels were assembled in a large cofferdam basin excavated alongside the Ohio River. The basin was then flooded and the segments floated out into the river. Each segment was towed upstream through two locks before reaching its final destination, approximately 29 miles.
The dam sits on 89 drilled shafts 78 inches in diameter and 40-foot-long rock-socketed. When the segments were transported to the site, they were aligned and then submerged in the river to sit on top of the shafts. The structure was then levelled and gaps between the river bottom and the precast unit were filled with concrete. The new dam structure is 82 feet high, about half of which is under water.
Market: Federal Heavy Civil
Service: Marine Infrastructure
Project Value: $125 million
Start Date: 1999
Completion Date: 2004