Background
Located in Demopolis, AL, Demopolis Lock and Dam is a critical piece of infrastructure that allows for navigation of the Tombigbee River. In mid-January 2024 a large portion of the lock chamber sill broke off, causing the lock chamber to become immediately inoperable. Due to the large impact this damage caused, USACE deemed this an emergency project and brought Brennan on early in the design process to develop a quick, constructable solution. Brennan partnered with R&D Maintenance Services, Inc., a local maintenance contractor that regularly works with the USACE Mobile District, to perform the repairs.
Design/Solution
In cooperation with USACE and R&D Maintenance Services, Brennan assisted with a design to repair the lock chamber which included constructing a new concrete sill extending downstream to fill in the breached area and tie into the existing portions of the remaining sill concrete. Due to fluctuating tailwater elevations during this time of the year, the work needed to be performed underwater. To accommodate the underwater design, Brennan partnered with Westbrook Engineering and came up with a simple W-beam and EFCO formwork system that could be easily installed underwater. Additionally, large stainless steel bulkhead panels were fabricated to create cast-in-place monolith joints. This eliminated the need to form and pour the monoliths separately. After formwork was installed, Brennan placed 6 lifts of SCC and 1 lift of conventional concrete to reach the top elevation of the existing miter gate sill. Originally the cure time between lifts was set at 7 days. However, Brennan hired a thermal control engineer and the cure times were brought down to 3 days. This significantly reduced the overall project duration and allowed Brennan to complete the project before USACE’s cutoff date to reopen to the navigation industry.
Results/Lessons Learned
The repairs to the lock chamber were completed and the lock was opened to navigation in mid May, two weeks ahead of the target lock opening date set by USACE. Internal concrete temperatures and differentials stayed within limits of the thermal control plan and no substantial concrete cracking was observed on the vertical face or top slab of the new sill concrete. This was considered a great success given the rapid time frame of the design phase. Not only was the lock chamber opened prior to the target date, Brennan also provided a long term solution for USACE with a quality end product similar to that of a normal project timeline.
General Comments
Brennan has performed several large underwater concrete projects in recent years, proving their expertise in delivering innovative and effective solutions for underwater formwork and concrete placements.
