Friday, November 4 was set to be a major milestone for the Port of Miami Tunnel. After years of planning and design, and having weathered the financial crisis by lining up a new equity partner, the project seemed to be on course for smooth sailing in 2011.
The Herrenknecht TBM arrived in Miami this summer and assembly work began on the massive machine. The Friday launch ceremony was just within reach when a lone city council member of a nearby town brought everything to a halt over concerns about where spoil would be dumped.
On the following Friday, the TBM started up, though local officials and the MAT (Miami Access Tunnel) concessionaire of Bouygues Travaux Publics and Meridiam Infrastructure were ironing out the details for where all of the spoil would end up as T&TNA went to press.
The two tunnel drives, each a little more than 1km in length, will make a gradual “S” shape as they connect Watson Island and the Port of Miami (on Dodge Island) beneath Government Cut. Each tunnel will have a 12.8m outside diameter and contain two traffic lanes, curbs, walkways, ventilation fans and safety features.
Since the project reached financial close in October 2009, design and build details were being finalized along with other preparatory work for the tunnel. This summer saw much progress as the MAT concessionaire worked toward the November launch.
Location and set up
The launch area for the TBM is quite constricted. The project is limited to working in FDOT’s right of way and also needed to lease property from the City of Miami to use for logistics staging, spoil staging and loading activity. Located on Watson Island, the tunnel starts in the median of MacArthur Causeway. Before the launch area could be excavated, the median needed to be widened to accommodate everything.
Excavations for the launch pit started this May. Roughly 100ft (30.5m) wide and 400ft (121.9m) long, it starts at ground level on one end and slopes down to a depth of 50ft (15.2m). From ground level to the portal there is a 5 per cent Slope. The reception pit on Dodge Island will be the same shape and dimension.
Large excavators were used for the launch area, however the ground proved to be too hard and difficult for standard backhoe equipment and needed to be pre-drilled. In the deepest part of the pit, there was pre-drilling 55ft (16.8m) in depth to loosen the ground prior to excavation.
“We took it down in two stages,” says Rick Wilson, COO and technical manager for the project. “The first stage we excavated deep enough in order to put the tie-backs in the side to hold the top part of the excavation back, and then after that was done we went on down to the grade level that we needed.”
He adds, “The geology varies quite a bit through the excavation. But it goes all the way from loose sand to strongly cemented limestone. So it was the strongly cemented limestone that needed to be pre-drilled.”
To support the excavation the project is using CSM panels on three sides and those are reinforced with tie-downs. On the bottom of the shaft there are 55ft tiedowns. “It worked out quite well,” Wilson says. “We had some water that we had to deal with coming from the bottom, but we’re dealing with that successfully.”
Excavation has started for the receiving shaft on Dodge Island, which will be the same shape and size as the launch shaft. “We’ve excavated down deep enough within the CSM walls so that we can do the tie-backs at the top,” Wilson explains.
As a subcontractor to Bouygues, Malcolm Drilling Company has constructed two sets of support of excavation, break-in and break-out plugs and soil improvement for the launch and reception of the TBM on each island.
To construct the 114ft wide by 62ft long by 50ft deep (35m, 19m, 15m) TBM plug on Watson Island for the TBM launch, Malcolm Drilling used a BG 40 BCM-10 CSM and a BG 50 equipped with a 12ft (3.65m) rock digging bucket constructed for the job by Continental Tool Company. “The CSM boxes along with the 12ft (3.65m) secant piles make up the break-in plug for the TBM,” says Wayne Broughton, superintendent, Malcolm Drilling.
After the TBM penetrates approximately 40ft (12m) into the plug, the sealing system between the tunnel shield and the pre-cast concrete segments can be installed.
Other subcontractors include Nicholson Construction, which announced in October it had been awarded a multi-million dollar contract to perform grout work that will fill voids in the existing rock layer with mortar grout mix.
A portion of Nicholson’s drilling and grouting work is being performed on-shore at Watson Island, while the other portion will be performed off-shore, using barges on the channel between Watson Island and the Port of Miami—based on the area’s cruise ships’ schedule. The offshore drilling and grouting will be performed under a double confinement system in order to avoid channel pollution.
Drilling operations will be recorded via a drilling parameter recording system. Nicholson reports all of the grouting work will be monitored using ‘Grout I.T.’, a Soletanche Bachy computerized control and data collection system.
“We are very pleased to be part of such a renowned geotechnical construction team, working alongside Herrenknecht and Bouygues Civil Works Florida,” says Laurent Lefebvre, executive vice president of Nicholson Construction.
Precast production
MAT has constructed a precast plant roughly 10 miles (16.1km) west of the work site and is producing the precast tunnel segments itself. As of the launch date, more than 2,000 of the total 12,000 segments have been manufactured and stored. The project requires four days of segments to be stored at all times.
Each segment measures 6.5m long, 7ft (2.1m) wide and 2ft (0.6m) thick, and weighs 12t. One ring consists of eight segments and a keystone. The plant has four production lines of eight molds each and 32 segments are produced each day. For reinforcement, rebar cages are being made off site by a subcontractor and are trucked to the precast plant.
Self-production of precast segments is something Bouygues has experience doing, and many of the local companies couldn’t compare, explains Wilson. “They have precast experience, but not the kind of tolerances that we have to deal with here. The segments have to be guaranteed for 150 years. So we had to work out an entirely new testing protocol with our client, FDOT, in order to produce segments that would be acceptable.”
To the Port and back
The Herrenknecht TBM with a 12.86m diameter arrived in Miami in June. Earlier this spring, the TBM was shipped to Holland on barges and trucks before the components were loaded onto a ship to sail to the Port of Miami. Once it arrived at the port everything was offloaded onto barges. The actual port is on Dodge Island, so all barges had to be moved to Watson Island where the TBM would launch. Roll-on/roll-off vehicles brought the TBM off of the barge and across the MacArthur Causeway in the middle of the night, stopping traffic for five nights straight.
During the next few months the TBM would be fully assembled with all six gantry cars prior to its launch in November.
“None of it was in the shaft when we started assembling it,” explains Wilson. “We had to lift everything with heavy cranes from the median area at grade to the shaft. The largest crane that we used was 800t capacity. It was a self-performed assembly. We had the rigging company assist us and we also brought in a team from Herrenknecht. They are still here as part of the commissioning and testing cycle that we’re going through right now.”
As the TBM started on November 11, the schedule projected eight months to excavate the first tunnel—the tube that travels eastbound to Dodge Island. There the TBM will make a U-turn before starting excavation on the westbound tube. “That will take about two and a half months, which will bring us up to next September,” Wilson says. Another six months is estimated for the second bore and operations for the TBM will remain on Watson Island for that drive. Or at least that’s the plan for now, he adds.
“We could have started at either side,” he says. “It just seems easier to start on Watson Island to support tunneling operations logistically. If we have to work out any process, it’s easier to do there than it will be on Dodge Island.”
Bouygues is running two 10-hour mining shifts and one four-hour maintenance shift every day, seven-days-a-week. There will be two interventions to inspect the cutterhead—before entering the channel on either drive. There are 107 disc cutter tools and 257 knife cutters on the TBM, and while wear prediction isn’t calculated, Wilson expected many of not all of the cutters will need to be replaced after the first bore.
Just days before the TBM’s launch ceremony, which, unbeknownst to most people, would not happen for another week, Wilson told TTNA the biggest challenge of the project is finishing on time.
He said, “It’s the same challenge that we have on most projects: staying on schedule, mitigating the set backs and things like that.
“So far we’ve managed to do that. This is a 55-month project to substantial completion and we’re right there.”
Machine assembly prior to drive Figure 1, The alignment between Watson Island and Dodge Island The TBM launches on the weekend of November 11-12
