Excavation wraps up on Miami Port link 10 May 2013
Peter Kenyon, TunnelTalk
The return drive for the Miami Port traffic tunnel is complete after the Herrenknecht hybrid TBM holed through for contractor Bouygues Civil Works Florida on its return leg to Watson Island.
Herrenknecht hybrid TBM breaks through

Herrenknecht hybrid TBM breaks through

"Progress on the project has, given the very unusual ground conditions, been remarkable with the mining of the westbound tube averaging four rings per day versus the three rings achieved on the eastbound tube," said the Miami Access Tunnel (MAT) Concessionaire CEO Trevor Jackson.
"With the tunnel boring now complete, the project has entered its final stages of M&E installation, finalization of buildings, and changes to the roads at either end. These tunnels will be the safest in the USA, having passive fire protection boards, active fire suppression in the form of a deluge system as well as cross passages as escape routes. Additionally there is complete safety protection from any storm surge with the two portal structures located above the maximum surge level and a failsafe of closing waterproof gates at either end."
Following Monday's (6 May 2013) breakthrough work now begins dismantling the giant TBM. "Whatever can be saved will be saved; the electric motors, the hydraulics. But all other parts will be recycled for future projects or just recycled," said MAT Vice President Chris Hodgkins. Work is scheduled to continue for another 12 months on fit-out, including building the two-lane highway inside each tunnel and completion of the remaining cross passages.
Western drive completed in six months

Western drive completed in six months

For the 1.1km westbound drive, which broke ground in October last year (2012) following successful completion of the parallel eastbound drive, advance rates were faster. Best daily advance was 16.76m, with a best weekly performance of 88.7m recorded during the six month return journey to Watson Island. The earlier drive, which launched in November 2011, took eight months to complete.
For the western drive to Watson Island 81 hyperbaric interventions were recorded for inspection and tool changes, for a total of 283 man entries. Entries to the excavation chamber were under pressures in the range of 0.7 bar to a maximum 3.1 bar. "The largest issues our TBM team encountered were mechanical breakdowns, which are neither unusual nor uncommon, and were addressed by our periodic maintenance plan," said the contractor's Director of Communications Luz Weinburg. At its deepest point the tunnel invert lies 36.5m below mean sea level.
For the twin drives a hybrid TBM system from Herrenknecht was selected. The machine operated in either the normal EPB mode, with material discharging from the screw conveyor onto a continuous conveyor muck hauling system, or in a 'water control process' (WCP) mode that bypassed the discharge gate and directed material from the screw conveyor through a mini-crusher and into a slurry pipeline circuit for pumping to a separation plant on the surface.
  • Undersea alignment of Miami Port Tunnel

    Undersea alignment of Miami Port Tunnel

  • Twin tunnels run under the Government Cut (left)

    Twin tunnels run under the Government Cut (left)

A straight EPB system was initially selected but subsequent geological investigations confirmed that additional technologies would be needed to manage conditions under the Cut. The geology was described as recent sedimentary carbonate rock with low consolidation and high variability, both horizontally and vertically, in terms of resistance, porosity and cohesion. Extra geological investigations also identified lower than anticipated fines content, making it not only too porous for a slurry operation, but also borderline favorable for efficient EBP operation in places.
The twin tube traffic tunnel and its associated works will create a new connection under the main shipping canal, the Government Cut channel, to the cruise and container port on Dodge Island. The new route will divert heavy port traffic away from the city streets of Miami and direct it instead through the tunnel and via a widening of the MacArthur Causeway and bridge from Watson Island to Interstate Highway I-395.
Bouygues Civil Works Florida, as contractor for the project, is a division of the giant French parent group Bouygues, which has a 10% stake in the private equity portion of the project's PPP procurement. Private equity group Meridiam holds the matching 90%. The US$607 million design-build construction contract is with the Miami Access Tunnel (MAT) group, which secured the 35-year PPP project in 2009. Transfield Services is contracted to operate and maintain the tunnel through the concession period. Client for the project comprises three public agencies: the Florida State Department of Transportation (FDOT), Miami-Dade County and the City of Miami. FDOT will make annual operating and maintenance payments to MAT once it is passed into service.

Gallery

References
First drive through for Miami Port link - TunnelTalk, August 2012
Groundbreaking gets Port of Miami Tunnel underway - TunnelTalk, July 2010

           

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