Builders Sweat Details of Creating a Parkway
Transportation builders are striving to create a true parkway in Central Florida
The $1.6-billion Wekiva Parkway project, a joint effort of the Central Florida Expressway Authority (CFX) and the Florida Dept. of Transportation (FDOT), has been lauded nationally and locally as a standout example of collaborative planning between infrastructure builders and environmental interest groups. (ENR 8/15 p. 52) But the 25-mile-long project, located in a mostly rural section of Central Florida north of Orlando—featuring rolling terrain, unusual for Florida—also represents the similarly rare opportunity for roadbuilders to design and construct a true “parkway” in a greenfield setting.
With both agencies mandated by Florida law to construct the nascent toll road as a “parkway”—though state legislators offered few other guidelines—officials with CFX and its engineering consultants began the business of determining what constituted such a designation.
The state provided “a pretty broad definition,” says Scott Bear, program manager with CH2M, the Wekiva Parkway corridor consultant. The regional transportation authority—and its consultants—took the de-facto lead in determining parkway guidelines by virtue of its sections being the first in line to be built.
“Our task was to make sure there was consistency” for the entirety of the 25-mile-long tollway,” Bear says. “A lot of discussion” ensued, he adds, with topics including the use of hardscape features, landscaping, the incorporation of natural buffers and even avoiding the creation of “BURPS”—short for big, ugly, rectangular ponds—when constructing the necessary water retention areas.
Glenn Pressimone, CFX director of engineering, was sure of one thing: that the mission for building a parkway “wasn’t going to be just throw concrete and asphalt out there.”
Seeking inspiration from existing parkways such as the Blue Ridge and others in New York and elsewhere, “We tried to keep as much of a rolling terrain” as possible, Bear says.
Bifurcation, or separation, of opposing travel lanes by utilizing wider medians, a fairly common approach, is another basic step being used to achieve a parkway feel. But Wekiva designers went a step further, by also using bifurcation on the vertical axis—a feature made possible by the area’s hilly terrain.
“So your northbound lanes could be anywhere from 7 to 10 feet below the southbound lanes,” Pressimone explains.
By having one set of travel lanes higher than the other, “You feel like you’re on a high-speed corridor,” Bear says.
Overall, engineers also designed a section where both sets of travel lanes go well below the existing terrain.
“We’re in a relatively rare part of the state where the water table is deep, so we can actually bring the roadway template down,” says Don Budnovich, CFX resident engineer. For instance, in one 1.5-mile-long stretch currently under construction, the mainline gradually dives nearly 25 ft below its natural elevation. This particular section almost went in the opposite direction, though, with early designs elevating the roadway by as much as 25 ft, Pressimone says.
“When we saw early cross sections, we saw that was a lot of dirt,” he says of the amount of fill that would’ve been required. However, project team members quickly began second-guessing that approach and started wondering about the water table and the possibility of doing a cut section—a relatively uncommon tactic for Florida, given its usually shallow water table.
But “lo and behold,” Pressimone says, “the water table was in our favor in those sections.”
Another standard approach to enhanced aesthetics that the project owners and engineers flipped in a non-standard way involved the detailing of the MSE (mechanically stabilized earth) walls supporting elevated sections.
“We wanted something that had a lot of reveal,” Pressimone says, adding that the intent was to mimic natural stone as much as possible. The project team eventually settled on an ashlar stone form liner for the MSE walls, but the selection process proved painstaking.
Design of these units was “easily a six-month or more process,” Bear says. “There was a lot of time spent on the finish of those retaining walls.”
For instance, instead of just painting the wall units, the project team devised a multi-step coating system comprising three differently colored stains that are sprayed on and, in some cases, sponged on.
Since the items would be used throughout the length of the 25-mile roadway—which is being built via separate contracts, contractors and even owners—the project team went through an exhaustive effort of producing multiple mock-ups in order to formally specify the production process and end result in the bidding documents.
Also, after deciding on a particular aesthetic, the project team kept those early mock-ups on hand, which suppliers must prove they can match perfectly before beginning work. To date, though, only one firm, Finishing Systems of Florida, has won the job for all awarded sections, according to CFX. Even so, it took “seven or eight” attempts to match the early mock-ups, Pressimone says.
Haunches for Arches
Another early idea for achieving a parkway feel was simply stated by Pressimone: “Let’s throw in some arches.” However, making that a reality would prove more complex.
To incorporate the arch look, the project team is using haunched beams for as many of the bridge structures as possible. (While most are concrete beams, some steel beams were required.)
One critical portion of the project is Section 2B, a 1.5-mile-long segment otherwise known as the Systems Interchange, which is being constructed by Southland Construction Co. under a $79.6-million contract. The contractor has a hard-and-fast deadline of January 2018, due to the segment’s function linking the new tollway with the existing S.R. 429.
Here, the 2,550-ft-long Ramp K, which flies over 429—which in turn flies over a local road—is the contractor’s critical path, says Albertos Ribas, with A2 Group, the section’s construction engineering and inspection (CEI) firm. Ramp K construction is made of five units that collectively include 17 spans measuring 150 ft long each, and, in all, 58 U-girder beams, 44 of them haunched. Units 1 and 2 each measure 600 ft in length and include four spans, while Units 3, 4 and 5 measure 450 ft long and include three spans.
“Ramp K will be the first thing to start and it’ll be the last thing to end (construction),” Ribas says. “It dominates this whole schedule for the project.”
Including the haunches in the beams, which adds weight, affected span lengths in some instances and otherwise challenged designers.
According to Kenneth Zagers, senior project manager with Atkins, and engineer of record for the Ramp K bridge, the structure uses PCI Zone 6 (Southeast region) U-girders, modified to include a haunch that varies between 72 in. and 115 in. in depth, depending on location.
“The haunches, an aesthetic requirement, add to the complexity of modeling the shape,” Zagers noted to ENR Southeast via email. For instance, he says, “We had to use a second-degree polynomial to define the curve of the haunch in order to accurately determine the stress in the structure.”
There are three basic segment types: an end segment, which includes a haunch on one end; a middle segment, that is haunched in the middle; and span segments, which lack a haunch and maintain a constant 72 in. depth.
Fabricating the haunched beams—some of which measure nearly 10 ft in height, versus the standard 6 ft—also proved more complex than usual, and added costs, says the precaster.
Beyond requiring the purchase of new forms for the haunched sections, “It also required our workers to be much higher in the air while tying the steel and placing the concrete for the members,” says Tim Morley, general manager for Dura-Stress. Additionally, the height of the beams and the additional steel reinforcement required to form the haunch sections resulted in more man-hours and a longer production cycle, he says. (Project officials admit that designing and constructing to parkway specifications adds a significant amount to the overall cost.)
Beam production is scheduled to commence in September, with delivery of the first beams set for October. So far so good for this critical segment, says Ribas: “(Southland’s) work on the substructure work is going extremely well. We are definitely on schedule.”