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Cianbro Hits Milestone in Shipyard Project

Published Wednesday Jun 23, 2021

Cianbro’s team of construction professionals at the company’s facility at Ricker’s Wharf in Portland has been working on a 5,000-ton concrete entrance structure for the Superflood Basin Project for the past year and a half and, on Sunday, June 20, a barge delivered the structure to its new home at Portsmouth Naval Shipyard.

Awarded to Cianbro in December 2019, the P-310 Superflood Project was the first phase of one of the largest infrastructure projects the Navy has undertaken at Portsmouth Naval Shipyard.

“This is a remarkable feat, and our team has truly risen to the challenge on one of the most technically complex projects our company has tackled,” said Andi Vigue, President & CEO of The Cianbro Companies. “The Superflood Project is a perfect example of the dedication and commitment of our team working to deliver quality outcomes; safely and on time.  We’re all very proud of their work, and now the construction team and others have the opportunity to celebrate all of that hard work, watching as the concrete entrance structure makes its way down the Fore River to its final destination.” 

In consideration of the Navy’s operational requirements and the limited shipyards with the capability to perform Portsmouth Naval Shipyard’s mission, contractors on the base must meet aggressive timelines, manage complex coordination challenges, and make schedule adjustments on short notice. Cianbro is committed to meeting these challenges at the shipyard in support of its mission.

The construction of the concrete entrance structure involves executing a sophisticated plan of jacking and ballasting to place the structure in the water on its foundation, where it will house an entrance caisson. Constructed and placed to tight tolerances, this caisson creates a locking system whereby water depths in the basin may be raised and lowered to meet operational requirements of the submarine fleet. 

The work onsite at the shipyard entailed construction of large concrete filled cellular cofferdams to extend the existing structures, fabrication, delivery and installation of the more than 5,000-ton precast concrete entrance structure, construction of temporary cofferdam cutoff walls, improvements to the existing granite wall via a sheet pile and concrete fill lining, dredging and rock blasting and removal, the addition of thousands of feet of landside concrete crane and trail rail systems, and modification to and addition of significant underground utilities needed to accommodate the superflood capability.


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