These 80-year-old structures are critical components of a system that ensures consistent navigability and access along the Mississippi River from Minnesota to the Gulf Coast. Due to their advanced age, the locks required increasingly complex rehabilitation work, particularly when it came to replacement of the anchorages—large hinges from which the miter gave leaves are hung. 

Photos courtesy of Massman Construction

Given the structures’ importance to river traffic, rehabilitation outages had to be kept to a minimum. Typically, the work begins with installation of 114-ft-wide bulkheads across the lock chamber to allow for removal of the upper miter gates. However, discovery of extensive damage of an upstream bulkhead recess slot at Lock 25 complicated the building team’s carefully mapped construction plans. Resequencing Lock 25 work between the two seasons enabled the team to integrate emergency repairs into the project’s limited budget and schedule, even with the design and fabrication of custom 30-ft-high stay-in-place formwork installed within a three-sided cofferdam.

Photos courtesy of Massman Construction

Following removal of the upper miter gates at both locks, the project team utilized specialized diamond wire saws for an around-the-clock effort that surgically removed approximately 2.5 million lb of concrete from around the embedded anchorages. Twelve anchorages underwent full replacement with components fabricated from 4-in.-thick steel plate while four others were partially replaced. The project also included electrical system rehabilitation and installation of new geotechnical instrumentation.

Photos courtesy of Massman Construction

A comprehensive safety plan spanning all disciplines involved in the project ensured all risks were addressed despite the expedited schedule. The plan covered facets ranging from accessing cofferdam work areas nearly 30 ft beneath the Mississippi’s surface to establishing controlled perimeters around wire-sawing operations.

Photos courtesy of Massman Construction

As a result, the project team logged more than 60,000 hours with no recordable incidents or lost-time injuries. Even with the unexpected repair needs, the project was completed ahead of schedule.