The U.S. Army Corps of Engineers Pittsburgh District successfully installed the two massive precast concrete cross culverts in the new middle wall at Monongahela River Lock and Dam 4 at Charleroi near Pittsburgh, Pa., Jan. 31.The $70.5 million work on monoliths M22 to M27 performed by Joseph B. Fay Company, Russellton, Pa., is part of the $2.7-billion Lower Monongahela Locks and Dams 2, 3, 4, or Lower Mon Project. The work underway at Charleroi involves building new middle and river walls that comprise a new riverside lock chamber.The 12-ft-high by 14-ft-wide by 34.5-ft-long precast culverts are stay-in elements within the new middle wall that will allow the future landside lock chamber to empty water from the chamber into the river.Each culvert weighed about 115 tons and was installed within tight tolerances and clearances inside a flooded coffer box work area. The entire lift weighed 130 tons with rigging."There were two tight points (the contractors) were concerned about and the clearance was in the range of inches," said Bob Burstynowicz, project engineer, Pittsburgh District.Using a large A-frame crane, the contractor "slowly and carefully" lowered the culverts into location onto and between the drilled foundation shafts that were constructed ahead of time, said Kirk McWilliams, resident engineer, Lower Mon Project Area Office."The installation was very challenging," said McWilliams. "The culverts had to be installed in a very precise location."A team of divers in the water ensured the culverts set down in their proper location and elevation. Army Corps engineers were challenged to determine how best to design and install the precast culverts so that the future land chamber could empty while not affecting the operation of the new river chamber, currently under construction, said Burstynowicz.Other challenges included achieving a minimum concrete compressive strength of 7,000 pounds per square inch, or PSI, that would "resist the load" the culverts placed on the foundation. After test panels failed to meet that requirement, engineers found a different solution. "We added additional reinforcing under the culvert to help distribute the load," said Burstynowicz. The contractor built the culverts on the deck of a barge using concrete from the project's onsite concrete batch plant, he added."It was a very successful operation," said McWilliams. "The culverts have been embedded in tremie concrete and we're ready for the next phase of construction." In a future contract option, the two culverts will be connected to the new river wall and emptying basin.