Tricky geology and a dense urban environment marked the journey of Harriet, a lone tunnel boring machine that excavated dual 1.26-kilometer-long, two-lane highway tunnels under the Government Cut shipping channel in Biscayne Bay, to connect Dodge and Watson islands. The tunnels, plus approximately 4 km of roadway and a bridge widening, create a link to the PortMiami from Interstates 395 and 95, taking some 16,000 daily trucks off local streets.

Completed this summer, the $710-million PortMiami Tunnel project features the first large-diameter tunnels—with internal diameters of 11.3 meters—to be constructed through Florida's challenging carbonate sedimentary strata, requiring one of the state's most comprehensive ground investigations. Until this project, only shallow, small-diameter tunnels had ever been built in the state.