Tunneling Under Water Makes Port of Miami Project a Challenge

Infrastructure Drilling Job to Ease Traffic Backups

TBM Tunnel Boring Machine — The Tunnel Boring Machine, or TBM, breaks out in July 2012 on the east side of the Miami Port project. Officials expect the completed tunnels to alleviate traffic congestion leading to and from the port. Source: Florida

The TBM was built by the German manufacturer Herrenknecht. At the start of the project it was the largest diameter soft ground TBM in the United States.

Harriet Tunnel Boring Machine — The Tunnel Boring Machine, dubbed Harriet, breaks ground in the launching pit on the western side of the tunnel. Harriet took her name from Harriet Tubman, the abolitionist known for the Underground Railroad in the 1850s and 1860s.

Harriet TunWorkers built the cement frame of Miami tunne — Workers built the cement frame of the tunnel in the wake of the tunnel borer. Source: Florida Department of Transportation photos Department of Transportation photos

The Port of Miami has been a problem since the Reagan administration, causing traffic snarls and wasted time. Nearly 16,000 vehicles—almost 5,000 of which are semi trucks—travel to and from the port each day. Because the traffic to get to the port winds through downtown Miami, it creates a lot of congestion. Thousands of vehicles have chosen to bypass this route entirely because it’s such a mess, opting to take a route through the Everglades instead.

Despite the fact that state officials have long been aware of the need to expand the Port of Miami, getting permission and funding to enact the project has been a matter of contention since the early 1980s. Back then, the port was only connected to the mainland by a two-lane road with a drawbridge. The government proposed to connect the port to the mainland by a tunnel, but the plan was scrapped in favor of a six-lane bridge instead.

The project has remained controversial since its introduction, though, and came close to being killed several times. According to Liz Fernandez at the Florida Department of Transportation, financing challenges nearly derailed the completion of the $1.062 billion project several times. By deciding to make it a public-private partnership instead of a strictly privately funded one, the tunnel avoids needing to charge tolls.

“The contract for this project was different from any other one we’ve worked on,” said Fernandez, with the FDOT, District 6. “There are no tolls in the concession agreement, meaning that the public sector assumes all the risks. This concept for funding won the Project Deal of the Year for 2009.”

Once the city of Miami and Broward County agreed to contribute the shared funding, the project could finally move forward. The scope of the project was nothing short of ambitious.

“The project comprises of the construction of dual 37-foot diameter, eight-tenths of a mile long, two-lane highway tunnels between the two man-made islands of Watson and Dodge and under the Government Cut shipping channel in Biscayne Bay, a state-designated aquatic preserve. In addition to the tunnels, the project includes approximately two and a half miles of roadway and access improvements on Dodge and the widening of the MacArthur bride and causeway on Watson,” said Luz Weinberg, director of communications for Bouygues Civil Works Florida, the contractor working on the project.

Geological conditions also made the project more challenging.

“The geological conditions under Government Cut are extremely unique because they’re soft limestone, and tunnels have never been built in those conditions before,” Fernandez said. The tunnel is also the first one in the United States that has a passive fire protection system, built with specially treated fireproof concrete panels.

Compensating for these conditions required some extra planning.

“These underground conditions were our main construction obstacles,”

Weinberg said. “We developed a Complementary Geotechnical Investigation Report, in which we were able to identify eight different types of weak rock layers. Consequently, they completed a sub-surface method plan in which they proposed ways to mitigate the typical challenges under soft-ground conditions such as water intrusion, face stability of the excavation and ground support for operations.”

Ultimately, the contractor constructed cross passages and created tunnels through the eight layers of earth by using hydraulic mucking and by using the earth-pressure-balance method (EPBM).

The construction crew used a 43-foot diameter tunnel-boring machine called Harriet, which was specifically created for this project. Another company, Malcolm Drilling, had to come in to work on shallow soil mixing for another phase of the project. This had to be placed to a depth to 23 feet.

To work within site spacing limits, the tunnels were brought together at both ends into one single shaft, creating a separation of only 14 feet between them. Malcolm Drilling used Cutter Soil Mixing barrettes to ensure that the tunnels remained stable during construction.

Because the ground conditions were less stable, Malcolm used cutter soil mixing panels to allow the team of Bouygues divers to access the cutterhead. They will also use advanced grouting techniques to enable ground freezing to construct two of the five cross passages that link the two tunnels.

Despite the incredible number of obstacles faced in getting to the point of beginning this project and the geological challenges involved in completing it, the project is finally moving along on schedule. According to Fernandez, the tunnel is on schedule to open to traffic as of May 2014.