Supporting the Elevated Boardwalk with Helical Piles at Pracht Wetlands

Thursday, May 28th, 2020 by Kendra Dunnigan

Challenge

The City of Wichita, KS had plans for an interactive eco-tourism park in the northwest corner of the city. Pracht Wetlands Park is a 91-acre natural waterfowl wetlands habitat and a first of its kind attraction. The centerpiece is a 12 ft wide, 1000+ ft long elevated boardwalk that winds throughout the park. The plan will be completed in 3 phases.

Designing the boardwalk with the desired elevation (4 ft average above grade) created issues around lateral buckling of the boardwalk over time. Installation of the project took place during the rainy season, making access to the wetland and moving around the site a complicated process. Additionally, we had to keep environmental concerns top of mind in our approach to the project so as not to disrupt the delicate ecosystem of the wetland.

Solution

Helical piles were chosen as the ideal deep foundation solution to support the new boardwalk. They were selected over other proposed solutions due to accessibility issues in the wetland and the ability to install them quickly, keeping pace with a tight construction schedule. The helical pile design included eighty (80) Model 450 (4.50-inch OD by 0. 337-inch wall) round shaft helical piles with an 8”- 10”- 12” helix plate configuration to support design working compression loads up to 60 kips. There were also thirty-three (33) Model 287 (2.875-inch OD by 0.203-inch wall) round shaft helical piles with an 8”-10” helix plate configuration, installed at a 30-degree batter to provide up to 16 kips of lateral restraint. The model 450 piles were installed every twenty-four (24) feet with two piles at each location, while the model 287 piles were installed alongside specific vertical pile locations and attached with a custom clamshell and clevis bracket.

The vertical piles were advanced to depths of 21 to 28 feet to achieve torque-correlated ultimate capacities of at least twice the design working loads. Installation of the project took place during the rainy season, making access to the wetland and moving around the site, complicated. In order to complete the installation, water-filled dams had to be placed around the perimeter of the project area in advance. Large pumps were then used to remove water and muck from that area to allow for manageable access. Due to the wetland conditions and the need for extra reach to install piles, a large 314 CAT track hoe was used to install all pile locations rather than typical smaller equipment. Every precaution was taken to limit the impact of the construction on the protected wetland and avoid potential damage from man and machine.

Results:

The project was completed in 15 working days with a 3-person crew. “The engineers were amazed at how quickly we were able to stage our materials and get them in place,” said Brent Foreman, Thrasher Project Lead. “People are always amazed by how much and how fast we get things done with the small crews that we run.” Hutton Construction Team Lead, Jason Gillig added, “Thrasher was an integral part of our team from the very start, helping not just Hutton with planning and construction coordination but our architect and engineering partners as well. Thrasher even met with the engineers in person to iron out the final design, layout and connection details. Thrasher and their product was a perfect fit for this project and a big part of its success.”

“Thrasher was an integral part of our team from the very start, helping not just Hutton with planning and construction coordination but our architect and engineering partners as well. Thrasher even met with the engineers in person to iron out the final design, layout and connection details. Thrasher and their product was a perfect fit for this project and a big part of its success.”