The US Army Corps of Engineers (USACE), Pittsburgh District is the Owner of the Charleroi Locks and Dam 4 New River Wall Project, located on the Monongahela River in Monessen, PA. The Charleroi Locks and Dam 4 is one of nine structures which provide for year-round navigation on the Monongahela River between Pittsburgh, PA and Fairmont, WV. Charleroi Locks and Dam 4 consists of two lock chambers and a gated dam. This type of dam is constructed to permit increased control over the water level in the navigation pool upriver.
The new River Wall project is a component of a larger effort to improve and modernize the navigation facilities on the Lower Monongahela River between Braddock and Charleroi. The modernization effort at this site in Charleroi will ultimately result in the construction of two new 84-feet wide chambers to replace the existing 56-feet wide locks. The New River Wall portion of the work involved construction of an 884-feet long wall, with 459-feet on the upstream side of the dam and 425-feet on the downstream side, and is an extension of an existing stub wall. Performed as a joint venture by Trumbull Corporation and Brayman Construction Corporation, the work included a significant amount of “in-the -wet” construction techniques for the drilled shaft foundation system and concrete placements. Installation of 144-each drilled shafts was required to support the wall: 30-each 54-inch diameter and 114-each 78-inch diameter. All concrete placements for the drilled shafts were performed using underwater tremie placement techniques. The maximum concrete lifts were 15-feet and individually required three lifts. The top of each lift had to be cleaned by the diving team, prior to placement. Of the 21 new monoliths constructed to form the wall, 15 required “in-the-wet” techniques.
Following the dredging and drilled shaft work, 40-ton rebar cages were assembled on the surface and lowered to the bottom of the river using two floating cranes. Gang panels were then lowered into the water and assembled by divers to form the four sides of the monolith. When the form was complete, a tremie pipe was inserted inside the form to the bottom of the river and concrete placement began. The remaining six monoliths demanded construction of large cofferboxes. A total of 106 mass concrete pours and 47 underwater tremie placements were completed by the end of the project.
The contract also required the team to design and provide a state-of-the-art concrete batch plant, as well as to develop a large dredge material disposal site for this and future USACE contracts. The team furnished and installed a 2,000-LF conveyor system to supply concrete to the monolith and caisson concrete placements within three minutes of batching. The constructed batch plant had the capability to produce 180-CY per hour of project-specific concrete. In all, the project placed over 70,000-CY of concrete.
In addition, the New River Wall Project involved underwater installation of 14-each rock anchors with an innovative above-water approach. Our approach minimized diver utilization and allowed the team to overcome artesian conditions. Additional features on the project included de-watering, sheet pile installation, and the fabrication and installation of custom large fill/emptying valves with mechanical embeds. For those monoliths, which did not require de-watering, sheet piling (cut off wall) was driven and cut to grade prior to the first lift of mass concrete placement. This work was accomplished utilizing floating plants and divers. Full depth forms and the tremie placement method were then utilized for the underwater mass lifts.