Virtual Control: Five scans stitched together capture the gate leaves. Gear rings and hinges were next
Image courtesy of Alberici Constructors

Mitchell Collins, chief surveyor with Alberici Constructors, St. Louis, helped take laser scanning and precision fabrication and concrete placement to new heights in 2012 on the Seabrook Floodgate Complex for the U.S. Army Corps of Engineers in New Orleans.


The schedule-driven project—which includes two 120-ton vertical-lift gates and one sector gate with a pair of 235-ton sector leaves—required tight dimensional control in fabrication and construction. Traditionally, that control would be assured by dry-fitting fabricated parts to place embeds accurately; the parts would then be removed for secondary pours.

But the contractor decided to have Collins laser-scan the parts during fabrication at Alberici's Hillsdale Fabricators, St. Louis, to ensure they conformed to the design dimensions and model them in 3D. Then, he scanned the install locations in New Orleans to verify fit and guide the secondary pours—all as the parts were still being created 600 miles away.

"That saved us many weeks," says Dave Calcaterra, Alberici Constructors vice president of operations and project manager on the Seabrook job. Alberici had committed to deliver the complex by July. "I don't think we would have made that date without Mitch using his lasers, verifying dimensions of the gates and having them fit-tested by scanning," he says.

"The fabricators did a fantastic job," says Collins, quick to deflect credit to his colleagues. The complex, 35-ft-tall sector-gate leaves each has a radius of 73 ft and forms a 70º angle. I-beams were rolled into curves to form the horizontal beams to support the skin plates; vertical I-beams were welded to the horizontals and to the radii from the center axis. "There are a lot of steel members, and all that welding at different times tends to pull that steel one way or the other," Collins says. "I used the scanner to make sure they were geometrically correct."

Calcaterra says Collins understands his tools, applies them well and can be depended on to accomplish what needs to be done. "That's not common. A lot of guys, you have to check up on and then have a third party check their work when they are done. He was pretty much on his own. He was our QA guy," Calcaterra says.