Doing Big Things in Small Spaces. 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, a colossal Herrenknecht tunnel-boring machine (TBM) and the Brokk 400.

The Brokk 400, while nearly 1,400 times smaller than the TBM, is tenaciously excavating away to create five cross passages between the twin traffic tunnels under Biscayne Bay.

Design-build contractor Bouygues Civil Works Florida is using the compact Brokk to create the 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. Mazzia said, “Considering the cramped space, challenges in safe excavation and the need to stabilize the ground around the passages, the Brokk’s power, precision, size and versatility made it the right tool for the job.”

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.

“The most challenging aspect is definitely the confined space,” said Eric Deltour, the Bouygues cross passages superintendent. “This is different than traditional mining, where the miners have room to excavate. With the Brokk, our crews are able to get right in there and easily get the excavated material out.”

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’s power is on full display as it proficiently breaks through materials while reducing time, effort and potential hazards for the workers involved. “This is the perfect machine for this part of the project,” said Mazzia.