Contractors working for the U.S. Army Corps of Engineers Pittsburgh District install a 23-foot-tall concrete shaft enclosure weighing approximately 120,000 pounds as part of the guard wall at the Monongahela River Locks and Dam 4 in Charleroi, Pennsylvania, Nov. 16, 2023. The contractor utilized an A-frame crane named "Big Al" to lift, relocate, and position the shaft enclosure. Over nearly two decades, the Pittsburgh District has been engaged in constructing a new 720-foot-long by 84-foot-wide navigation chamber in Charleroi. This year, they filled the chamber with water and installed new miter gates. The completion of the guard wall constitutes the final phase of this extensive construction project. (U.S. Army Corps of Engineers Pittsburgh District photo by Michel Sauret)