A New Rail Bridge for the New River

$53 Million High-Level Bridge Caps SFRTA’s Double-Tracking Effort

By Debra Wood

After experiencing significant increases in Tri-Rail ridership, the South Florida Regional Transportation Authority decided to double track its entire 72-mi corridor, enabling it to increase the number of trains and decrease wait times. The recent completion of the $53 million high-level New River Bridge segment in Fort Lauderdale wraps up the five-year, $333.8 million initiative.

“It will make a difference to passengers,” SFRTA spokesperson Bonnie Arnold says of the overall double-tracking effort. “We will go from 40 to 50 trains a day.”

About 12,200 people ride Tri-Rail daily, up 30% from 2006. The track runs from Miami to West Palm Beach.

The recently completed Tri-Rail bridge replaces an 85-year-old bascule bridge. (CSX will continue to use the existing track and bascule bridge for its freight trains.) Prior to the new New River Bridge, however, nautical traffic had priority over rail and often delayed train travelers, Arnold says. The new bridge provides 55 ft of clearance above the South Fork of the New River at mean tide.

Washington Group International of Boise, Idaho, received the $53 million New River design-build contract in July 2003 from SFRTA. The Florida Department of Transportation owns the rail corridor, provided oversight during construction, and will maintain the bridge.

The firm designed the 3,688-ft-long bridge with 94-ft-long spans of cast-in-place concrete with precast concrete girders and a cast-in-place concrete deck. An additional 2,600 lin. ft of approaches employ T-Wall earth-retention structures.

advertisement

The firm lengthened span distance, decreasing the number of spans, and employed a single round column and cap design, rather than the original four 6-ft drilled shafts per column the rail line planned. A limited work area, only 40-ft wide, positioned between Interstate 595 and the active rail line along the Interstate 95 corridor, led engineers to re-evaluate those original plans.

The use of these single, nonredundant piers helped the project’s progress considerably, says Rod Woodhouse, design manager for Washington Group.

“Because we would have had to put in the sheet pile, drill the four drilled shafts and put the cap on it, it would have effectively eliminated travel along the corridor as we built the columns and caps,” Wilbor adds. By using nonredundant shafts, “it allowed us to build sequentially instead of trying to build the entire (pier) structure straight up and then move to the next and move to the next. Access was a huge issue.”

Woodhouse estimates it would have taken three to four weeks for construction workers to complete each four-shaft/pile cap foundation, before they could move the cranes to the next one.

“The single shaft didn’t create a roadblock,” he says. “We could get around it with the drilling crane.” The drilled shafts average 80 ft long.

In addition to saving time, Washington Group estimates the use of single-shaft piers shaved about $17 million off the price of the project. A single 10-ft pier cost about 25-30% more than the 6-ft. piers, but the design called for far fewer of them.

Bridge subcontractor GLF Construction Corp. of Miami subcontracted the drilled-shaft foundation work to Case Atlantic Co. of Clearwater, Fla., and began drilled-shaft testing in July 2004.

The size of the shafts presented their own hurdles.

 “The 10-ft-diameter drilled shafts were the first in Florida of that size and the first in Florida to be considered mass concrete that not only required temperature monitoring but cooling pipes to keep them cool while they cured,” says Joe Beaird, project manager for GLF.

Using a system designed by CTL Group of Skokie, Ill., GLF installed four cooling tubes, with thermo-coupled temperature monitoring equipment at three locations along the axis of the shaft and perimeter. River water flowed through steel pipe embedded in the concrete to dissipate heat buildup during the curing process. GLF monitored the temperature every two hours, comparing the differential between the center and perimeter.

The project team added fly ash to the concrete mix used for everything from the drilled shafts to the decks.

“Fly ash supports a lower heat of hydration in the concrete, which creates less heat buildup and [decreases the] opportunity for cracking,” Wilbor says. (At one point fly ash became unavailable, so Washington Group substituted steel slag.)

Once Case Atlantic completed the shafts, GLF built the columns, caps, girders, main span steel and deck. It employed an overhead-launching truss to erect each of the 228 94-ft-long, 54-ton girders. The company set 24 spans in three months, and during its best week set four spans.

“Clearances between existing and new structures were often measured in inches,” Wilbor adds. “Even formwork clearances had to be considered as part of the design.”

Engineers also widened the flanges on the six bridge girders, so they touched, avoiding the need for deck forms. The main span utilized a composite steel floor beam and concrete deck design, reducing the amount of steel in the floor beams by more than 500,000 lbs. The team used precast whenever possible.

Bergeron Land Development of Pembroke Pines, Fla., completed the earthwork and T-Wall approaches. The company installed a load-transfer platform over the high organic soils, which is supported by vibratory concrete columns placed by Hayward Baker of Pompano Beach, Fla.

Once GLF finished the bridge, Herzog Contracting Corp. of Pompano Beach, laid the track, and the bridge opened for train traffic in April.

New River Rail Bridge Project Team
Owner: South Florida Regional Transportation Authority
Prime Contractor: Washington Group International, Boise, Idaho
Design: Washington Group International, Deerfield Beach, Fla.
Construction Management: Rust Constructors, a subsidiary of Washington Group
Foundations and Bridge structure: GLF Construction Corp., Miami
Earthwork and T-Wall approaches: Bergeron Land Development, Pembroke Pines, Fla.
Ground stabilization: Hayward Baker, Pompano Beach, Fla.
Track installation: Herzog Contracting Corp., Pompano Beach, Fla.
Drilled Shaft Design and Civil Testing: Williams Earth Sciences, Largo, Fla.

Useful Sources:
Tri-Rail Double Track Corridor Improvement Program
http://www.tri-rail.com/double_tracking/fact_sheet.htm