Challenging bulkhead design: Dam closure system at Broken Bow and Hugo Lakes
Tulsa District of the U.S. Army Corps of Engineers would like to replace the bulkheads at Broken Bow and Hugo Lakes. These bulkheads are used to block water from flowing through the tainter gate bays when the tainter gates are serviced or inspected.
In 2015, the Mead & Hunt team analyzed the feasibility of multiple gate closure systems and provided a life-cycle cost for each system. The project was a great opportunity for my team to demonstrate our dam safety expertise on a large USACE project. The final report recommended Tulsa District procure a single segmental bulkhead to be used at both lakes.
Segmental bulkhead designs are widely used as a closure system. They have the advantage of being fully shop-fabricated with relatively light sections that can be removed from the water with a medium-sized crane. Assembly of a segmental bulkhead in the water requires proper alignment of bulkhead sections followed by fastening the sections together in a safe and reliable manner.
Last year, the district issued a task order to our Mason & Hanger and Mead & Hunt Joint Venture. We were asked to provide a preliminary design and cost estimate for a single segmental bulkhead system to be used at two dams. Our design had to include storage locations and each lake and launch locations for the bulkhead system.
The scope of work included a number of design constraints:
- No divers could be employed for assembly or placement of the bulkhead
- Use of only one crane for loading, unloading and assembly
- Minimize the number of personnel required to transport, mobilize and demobilize
- A six-foot operating reservoir level range at each project
- Challenging geometry at one of the launch sites
Our team used an iterative design approach that satisfied the design constraints. We varied the external dimensions and wall thickness of the bulkhead segments until a design for the segmental bulkhead system was achieved.
The resulting segmental bulkhead consists of individual segments that when joined constitute a bulkhead floating in a horizontal orientation. The bulkhead can be ballasted to rotate to a vertical orientation for placement at the upstream end of a spillway bay. Different combinations of the segments can be assembled to produce a bulkhead for use at both lakes.
The segments will be joined using pin and socket joints, tension connectors and flange bolts. These connection systems have a tolerance for misalignment as the segments are moved together. In addition, the systems permit assembly personnel to remain clear of pinch points during assembly. No divers are required for assembly or placement of the bulkhead.
Launch access at both lakes was considered, to allow the use of the district’s crane. Part of the design included developing a crane pad that limited the required crane radius and allowed deployment and recovery of the designed bulkhead segments.
Last week we submitted the final 65 percent design. I’m looking forward to working with Tulsa District to complete the design and see this system constructed and placed into operation. This exacting project has helped me hone my skills as a project manager and engineer.
I would love to discuss this very interesting dam closure system design project with you. I’ll be at the Society of American Military Engineers Federal Small Business Conference in Pittsburgh from November 15-17. Come visit me at Mead & Hunt booth #712.
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