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A Sensitive Build

Water to the west, structures to the north and south and a tunnel below create a demanding construction environment for new Austal USA shipbuilding bay.










Project Name: Austal Assembly Bay 5
Location: Mobile
Construction Manager: Keith Howell, Thompson Engineering
Engineer: Thompson Engineering
Lead Structural-Robert Harvey
Lead Civil-Wade Burcham
Design/Build General Contractor: Thompson Engineering
Architect: Sandy McArthur, Watermark Design
Major Subcontractors: Jordan Pile Driving Inc. (auger cast piles); A & B Electric (electrical and fire alarm); SJ&L Contractors (site work and storm drainage)
Project Construction Value (Assembly Bay 5): $18 million
Project Construction Value of Assembly Bay 5 and the Cove Reclamation Project: $30 million

Austal USA, the Mobile-based North American headquarters of the Australian shipbuilding company, employs more than 1,000 people in the Mobile Bay area. As the company works to build ships for the U.S. Navy, including 10 Joint High Speed Vessels as part of a $1.6 billion contract, new facilities are needed. In January, Austal USA selected Thompson Engineering to provide design and construction services on the newest Assembly Bay facility at its aluminum shipbuilding facility in Mobile. The new facility, known as Bay 5, will be used for the assembly of U.S. Navy combat ships. It spans more than 58,000 square feet, with a clear height of 102 feet and clear width of 125 feet.

Assembly Bay 5 will include a 30,000-square-foot steel mezzanine with two levels; multiple engineering, administrative and conferencing rooms; EMA stations, and assembly logistics facilities, says Henry Seawell, chairman of the board for Thompson Engineering. The project, which was designed to meet the latest International Building Code requirements, includes a massive amount of advanced technology aluminum hull fabrication and specialized welding and mechanical support equipment, as well as 12 offices on the ground floor level and five on the mezzanine upper level. The building was designed for three 40 metric ton capacity, top running double girder cranes, each having multiple 20 metric ton hoists. The exterior of the building includes full width rolling doors on the east and west sides, which are each 106 feet wide and 102 feet high.

Any project of this size is bound to have challenges, and Bay 5’s waterfront location adds to the challenge. First, the site poses a logistical problem for the workers. “There is very little working room at the site,” Seawell says. “With the existing Assembly Bay 6 immediately south of the structure and a 400-employee worker assembly and break room facility and structural bridge spanning over the Bankhead Tunnel to the north, minimum access is available for the delivery, storage and maneuvering of the large amounts of building materials needed to complete the project.”

To combat the issue of working space, Thompson Engineering’s project team crafted a unique deep foundation and design of the site and structure, along with a fast track schedule to ensure that the site could accommodate the project. At times, Thompson has also employed the rising structure as a construction staging and assembly facility. Engineers and project managers have had to stick to careful planning procedures to help satisfy the strict construction timeline.

Another, even greater challenge was the critically small land area available before construction began at this east bank Mobile River facility. “We were challenged to create stable and workable land areas next to and beneath the Bay 5 Facility with an initiative known as the Austal Cove Reclamation project,” Seawell says. “This previously undeveloped site, which had been created by the Highway Department in the 1940s when the historic Bankhead Tunnel was excavated and installed underwater, was an open water cove partially filled with extremely soft river sediments.”

To make the soft cove land stable and useful, Thompson designed and built a new bulkhead and filled the area to an elevation of 10 feet above sea level. “This was a sensitive build,” Seawell says. “The Bankhead Tunnel, completed in 1940, runs through and under the middle of the entire shipyard facility at this site.”

Designing and building the cove reclamation project required Thompson’s marine design expertise, Seawell says. For instance, the project involved using specialized ground improvement technology for the underlying weak sediments, below-water bracing systems for the marine retaining walls adjacent to the tunnel and long span pre-stressed concrete girders, and high capacity bridge spans supported on a combined pipe/sheet pile wall system designed to withstand heavy shipyard operations while assuring that no additional loading will be applied to the tunnel.

Once complete, the Austal Assembly Bay 5 will connect to the neighboring, smaller Assembly Bay 6 building to create a larger ship manufacturing facility. But the project will also pave the way for another future improvement: The new Assembly Bay will accommodate a future modification and rebuild of the existing Assembly Bay 6, which will create one large structure containing Assembly Bays 5 and 6 under a single roof.

Nancy Mann Jackson is a freelance writer for Business Alabama. She lives in Florence.

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