8 minute read
The Beauty of Environmental Design: How Wekiva Parkway Section 6 Harmonizes Progress & Good Stewardship
By Garrett Jones, PE
Garrett Jones is an engineer and project manager at Superior Construction. He is currently managing Superior’s I-4 and Daryl Carter Parkway Interchange project for the Florida Department of Transportation. Connect with him at GJones@superiorconstruction.com.
Heavy civil construction and environmental stewardship have often been at odds. Some view Florida’s economic development — stimulated by its thriving economy and growing population — as a threat to the state’s pristine natural habitats.
Balancing Florida's rapid development with the preservation of its unique landscapes is a delicate challenge, but it’s not impossible.
The WGI-Superior Construction design-build team’s $247 million Wekiva Parkway Section 6 project in Lake and Seminole Counties demonstrates how innovative engineering can harmonize progress while minimizing the environmental impact of construction.
Built across a federally designated Wild and Scenic River, Wekiva Parkway Section 6 is a vital stretch of the Florida Department of Transportation’s (FDOT’s) $1.6 billion Wekiva Parkway (SR 429). The Wekiva Parkway connects to SR 417, completing a beltway around Central Florida — home to unique springs, wetlands and diverse wildlife.
Segment 6 comprises nearly six miles of limited access toll road, primarily along the existing SR 46 corridor from SR 429 to just west of Longwood-Markham Road. Its centerpiece is the Wekiva River Crossing, a set of three side-by-side cast-in-place segmental bridges. The scope also included a non-tolled service road for local travel and nine wildlife bridges — allowing animals to pass safely between the Seminole State Forest and Rock Springs Run State Reserve — for a total of 18 bridges with over 1.268 million square feet of new bridge deck.
Protecting A Wild And Scenic River
The Wekiva River’s Federal Wild and Scenic River designation necessitated environmentally conscious construction methods. Throughout the preliminary design process, the WGI-Superior Construction team coordinated extensively with local agencies and stakeholders, including the National Park Service, to achieve approval in accordance with the National Wild and Scenic Rivers Act.
Each of the Wekiva River Crossing’s three complex 2,068-foot-long bridges included cast-in-place (CIP) concrete segmental spans totaling 880 feet with a 360-foot main span. They were constructed from the top down to eliminate work in the water, protect the surrounding environment during construction, and provide undisturbed and safe habitats for wildlife after completion. The design team and builder collaborated extensively during the design phase to ensure the custom form traveler would function as designed with the complex details associated with CIP segmental construction technologies.
“The bridge’s segmental superstructure is exceptionally durable thanks to being longitudinally post-tensioned and having a transversely post-tensioned top deck,” said Jerry Pfuntner, PE, SE of COWI (formerly Finley Engineering), the project's engineering firm responsible for the concrete segmental bridge design. “The superstructure and top deck surface remain in compression under permanent loads.
“Furthermore, cast-in-place segmental box girders have continuous bonded mild reinforcement along their interior and exterior surfaces. This reinforcement significantly increases capacity and durability, reducing the need for future maintenance.”
Access and staging were challenging due to the top-down approach. The design-build team’s solution utilized a carefully designed trestle to support large equipment access for pier substructures, minimizing the construction footprint and environmental impacts. The trestle allowed for the selective cutting of trees, preserving the natural environment to the greatest extent possible. Leaving a portion of the tree and the root systems intact facilitated erosion control and allowed for vegetation re-growth post-construction.
“To avoid environmental impacts when building the pier footings, we used a steel sheet pile cofferdam to contain materials during excavation,” said Superior Project Manager John Beltran.
Crews hauled away excavated soils and pumped discharge from dewatering activities into a sediment filter box. The team then used a concrete seal slab to minimize groundwater intrusion into the excavation.
To cut the piling two feet below the mud line, the team custom-fabricated a containment cell (see figure below) with an embedment plate at its bottom to ensure it was fully seated in the mud line. While carefully monitoring the water’s turbidity, floating barriers around the containment cell provided environmental protection by confining sediments that could adversely affect aquatic ecosystems. After crews removed all the piles within the cell, they pumped turbid water to the filter box on top of the bridge deck.
Because segmental construction requires post-tensioning systems that must be protected, Superior used a flexible filler of microcrystalline wax instead of grout to provide strand protection for continuity tendons, enabling tendon strand replacement over time if necessary.
For the conventional bridges, the design-build team used an overhang system that was delivered in 20-foot pre-constructed sections, enabling faster deck pours. Shelby Erectors — the team’s reinforcing steel and stay-in-place form installer — utilized a TyBot system, which uses lasers and cameras to make reinforcing steel tie connections, further speeding up production. RS&H performed construction, engineering and inspection services.
Devising Geotechnical Solutions
Several unforeseen conditions affected the project, including the COVID-19 pandemic and the discovery of several sinkholes throughout the project limits, which affected foundation installations at a couple of the bridge locations. Wood Environment & Infrastructure Solutions (Now WSP USA), an expert in Central Florida’s very challenging subsurface conditions, provided outstanding geotechnical solutions. Engineers redesigned the roadway with innovative traffic control plans to overcome five sinkholes and keep the project on schedule. Each sinkhole had a unique approach, as the geotechnical conditions represented different challenges.
The five relic sinkholes, filled with soft organic soils, were mitigated using rigid inclusions to increase the stability of the roadway embankments and to reduce future roadway settlements to tolerable levels.
Blending Into Nature
The Wekiva River Crossing’s main spans showcase the team’s commitment to structural efficiency and aesthetics.
“The community sought a railing that would have minimal visual obstruction of the Wekiva River," Pfuntner said. "To protect the viewshed, the team used a pedestrian rail that is minimally obtrusive but structurally sound.”
Engineers invoked the bridge's proportions to achieve the minimization target, ensuring it seamlessly integrated with the scenic environment.
The Superior-WGI team used a long box girder cantilever wing to decrease the bridge’s signature, increase shadows, add depth to the box girder webs, and reduce mass. The long wings also reduced the bottom soffit width and pier width.
This aesthetically pleasing geometry enhanced the user experience for pedestrians and boaters by reducing the bridge surface visible from the water and maximizing open space beneath the bridge. Relief patterns inspired by the main span piers grace the approach piers, reducing visual clutter and creating more open space beneath the superstructures.
The signature Wekiva River Crossing even features pier shapes inspired by trees and a concrete stain to match its surroundings. Its harmonious integration with the natural environment has garnered praise from its owner, residents and visitors, enriching the region's cultural landscape.
Transforming the Transportation Industry
Florida is renowned for its diverse wildlife and countless opportunities for outdoor recreational activities. The Wekiva Parkway Section 6 project respects this natural heritage while providing an exemplary transportation artery critical to the region's sustained growth.
"Section 6 of the Wekiva Parkway proves responsible engineering can integrate with sustainable development, and it sets a precedent for other regions facing similar challenges,” said Walter Kloss, PE, Vice President of Transportation Alternative Delivery for WGI, Inc.
As population growth continues, environmental design and engineering ingenuity can lead the way toward a more sustainable and prosperous future for the Sunshine State.
