Compact Brokk Adds Efficiency, Safety to Port of Miami Cross Passage Work
On a scale of one to 10 for massiveness, the Port of Miami Tunnel (POMT) project is a 15. Connecting Dodge Island to Watson Island with two traffic tunnels is only possible with the help of some heavy hitters, and the heaviest of all is a colossal Herrenknecht tunnel-boring machine (TBM). With its 42.3-foot diameter cutter head, the TBM is carving its way under Biscayne Bay.
But the TBM isn’t the only workhorse in the project. The Brokk 400, while nearly 1,400 times smaller than the star performer, is tenaciously excavating away to create the cross passages between the twin traffic tunnels.
Design-build contractor Bouygues Civil Works Florida is using the compact Brokk to create the five cross passages between the project’s twin 4,200-foot traffic tunnels. The passages provide escape routes between the tunnels, as well as maintenance access and storage space.
The Brokk 400 came to Miami courtesy of Alain Mazzia, the Bouygues plant and equipment manager responsible for sourcing equipment. He first ran into a Brokk on a nuclear waste project in France, and when he looked at the challenging factors of POMT cross passage excavation; the unique machines came to mind. “I knew the Brokk was dependable, as was the support from the company,” he said. “Also, the machine is a good combination of size, power and tools.”
At only 14 feet long, 5 feet wide and less than 6 feet tall, the Brokk is small enough to stay out of the way when it’s in the main tunnels, where crews and larger machines are constantly coming and going. The machine also maneuvers freely inside the relatively cramped space of the passages, which range in height and width from 10 to 14 feet.
Inside those passages, the Brokk 400 delivers tremendous force with a hydraulic breaker to excavate hard soil, some of which is being artificially reinforced with grout or through a freezing process to add stability. Once the material is excavated and sized, crews are using a bucket attachment to remove it from each passage.
The next step is to place support ribs at 3½-foot intervals. The machine grasps the top section of a steel rib with a beam manipulator retooled specifically for the job, carries it to the installation point, lifts and positions it, then holds it in place while miners bolt the lower sections to it.
Finally, the crews are using the Brokk for qualitative excavation, where the precision and sensitivity of its remote control allow the operator to approach theoretical limits without over-excavating.
Throughout the process, the Brokk enhances safety for the miners. The remote control keeps the operator away from potential cave-ins, and the electric-drive ensures crewmembers aren’t exposed to dangerous emissions.
“The Brokk 400 is powerful and precise, and it’s quite safe,” Mazzia said. “It’s been the perfect machine for this part of the project.”
