On May 6, tunnel crews with Bouygues Civil Works Florida completed the last leg of mining for the second of two, twin 4,200-ft-long tunnels for the $1-billion tunnel project at PortMiami. That morning, the project's 380-ft-long tunnel-boring machine—nicknamed Harriet—broke through for the last time, landing back on Watson Island, where it had first launched in November 2011.

After that initial launch, crews worked for nearly nine months boring the first tunnel under Biscayne Bay, breaking out on Dodge Island on July 31, 2012. To turn the TBM around and get it headed in the opposite direction, crews used a giant Teflon turntable to rotate the cutterhead and shield in preparation for boring the last twin tunnel and the trip back to Watson Island.

When completed, the tunnel will provide trucks servicing PortMiami with direct access to Interstate 395 and I-95. The design-build project—which is being delivered via a public-private partnership—marks the first time that a large-diameter tunnel has been bored through coralline limestone, which is highly porous and unstable.

Louis P. Brais, project executive with Bouygues, told ENR earlier this year that after Harriet's work is done, "there's a lot left to do." The project's deadline for final acceptance by the Florida Dept. of Transportation is August 2014.