Compact Work Under The Ocean In Miami

Nearly 16,000 vehicles travel through the Port of Miami, FL, daily, clogging downtown streets, creating safety hazards and restricting the port’s growth. With little land available above ground to expand roadways and bridge structures, the Port of Miami tunnel project will help relieve some of the congestion with the construction of twin tunnels. The total construction costs are estimated to be $607 million.

“Constrained space is the primary challenge for this project,” says Moneiba Hernandez, surface superintendent, Bouygues Civil Works Florida, the design-build contractor for the project. Providing compact equipment — including attachments — for support functions inside the tunnel boring machine and around the equally tight jobsite on shore, include a Bobcat T300 compact track loader, E50 compact excavator and nine 4×4 3400XL utility vehicles working in tandem on the 24/7 operation. The Bobcat machines and attachments were acquired from the local dealership, Bobcat of Metro Dade, in Hialeah Gardens, Fla.

Work began in 2010 and currently Bouygues Civil Works Florida is excavating under the ocean floor with a massive tunnel boring machine, manufactured in Germany, consisting of a four-story cutter head mounted on a body longer than a football field. It cuts a path between 23 to 43-feet a day, making way for the placement of a series of precast concrete segments.

These concrete walls form the rings of a 42-foot diameter tube that — when completed in 2014 — will contain two traffic lanes, curbs and walkways connecting Watson Island and the Port of Miami beneath Government Cut, the main shipping channel in Biscayne Bay. Once the tunnel boring machine reaches the southern side of the cut, it will be repositioned to cut an identical 4,200-foot tunnel back to the mainland. Altogether there will be four traffic lanes, two in each direction, to improve the traffic flow between Watson Island and the Port of Miami.

Efficiency underground
Despite its gigantic size, the workspace for support functions behind the cutter head varies from only 13- to 20-feet wide, and must be shared with water trucks, service vehicles and construction equipment. Also commanding real estate is a conveyor system that carries approximately 1,200 tons of excavated spoil per hour beyond the entrance. The compact E50 excavator’s small stature — only 18-feet long, 6 feet, 4-inches wide and 8 feet, 3-inches tall — allows it to easily remove spoil that drops beneath the conveyor without disrupting other traffic.

Bobcat 3400XL utility vehicles add more site maneuverability in the confined tunnel, says Chris Hodgkins, president of general contractor MAT Concessionaire LLC. The company purchased their own 3400XL to transport crews, inspection teams and tours of visiting media and dignitaries — including U.S. Secretary of Transportation Ray LaHood.

“The 3400XL is our contractor’s vehicle of choice for getting in and out of the tunnel. Because there’s a five-degree grade and the lowest point is 120 feet below sea level, we needed something quick, durable and reliable,” Hodgkins says.

The T300 is helping spread a cement-treated base and grading approximately 100-linear feet per day, which Hernandez says will eventually form the permanent road surface. “It is a very constrained space but the Bobcat loader is good because it can also move fast despite the restriction,” Hernandez says.

Compact productivity
On the mainland, the compact track loader is typically fitted with a bucket, a pallet fork or a sweeper to perform a variety of earthmoving and cleaning roles around the tunnel worksite’s limited space. Frequently, it is tasked with grading areas prior to crews pouring slabs or building service roads. Another daily function is removing backfill from an earthen wall. It also cleans the truck wheel washer bay, transferring multiple loads of accumulated site mud and debris to a spoil basin.

Hernandez has confidence in using the agile 81-horsepower compact track loader for any job involving earthwork, partly due to the track system’s combination of flotation and traction in mud and other challenging soil conditions. “The tracks help with maneuverability because the soil is sometimes sandy,” Hernandez adds.

The versatility of the E50 compact excavator’s attachments, including a hydraulic breaker, allows Bouygues Civil Works Florida crews to break up rock and existing pavement. The unit’s 12-inch trenching bucket and advanced hydraulics are used to dig trenches for the simultaneous installation of up to three utilities.

The compact excavator’s high breakout force assists operators in building a berm around the site’s spoil basin. It also is excavating a bed for the construction of site ponds, and is called upon again to perform the ponds’ finish work. “It is a versatile piece of equipment,” Hernandez says.

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