When Funding Became Available, Harrisburg Int’l Was Ready to Go With Levee Project

When Funding Became Available, Harrisburg Int’l Was Ready to Go With Levee Project
Author: 
Ken Wysocky
Published in: 
September
2021

The recent rehabilitation of an aging levee will help protect Harrisburg International Airport (MDT) from flooding for decades to come. In the meantime, the $22 million project also offers a valuable lesson about the benefits of planning ahead.

Nearly 20 years ago, the Pennsylvania airport began working with a design firm for plans to repair and rehabilitate a levee built by the United States Army Corps of Engineers to prevent flooding from the nearby Susquehanna River.

The 13,000-foot-long earthen structure, which runs along the west side of the airport’s 10,000-foot sole runway, faced increasing erosion problems caused by excessive vegetation growth, burrowing animals and damage inflicted by ice jams and other heavy debris.

facts&figures

Project: Levee Rehabilitation

Location: Harrisburg (PA) Int’l Airport

Approx. Cost: $22 million

Funding Sources: FAA; state of Pennsylvania; Susquehanna Area Regional Airport Authority

Funding: May 2019

Initial Design: 2004

Construction: Nov. 2019-June 2020

Design & Construction Management:
Urban Engineers Inc.

Consultant Subcontractor: Navarro & Wright Consulting Engineers Inc.

General Contractor: 
KC Construction

Geotextile Fabric: Contech Engineered Solutions (a Quikcrete company)

Key Benefit: Continued protection of runway & other critical infrastructure against flooding of nearby river

“It hadn’t reached the point where it threatened the integrity of our runway and other critical infrastructure, but we knew it ultimately would reach that point without rehabilitation,” says Tim Edwards, executive director at MDT. “We basically had a repair project fully designed in 2004, but there was no funding available from the FAA at the time.”

That changed in 2018, when the federal agency made special supplemental appropriation grants available to smaller airports with shovel-ready projects. With design work already completed, and 50,000 operations/1.2 million passengers handled in 2017, MDT met both major requirements.

“So we pulled the plan from the shelf, dusted it off and updated it,” Edwards explains. The airport promptly submitted an application for a $20.2 million grant, which FAA approved in May 2019. It’s the largest federal grant the airport has ever received, Edwards notes.

“I guess you could say we were in the right place at the right time,” he adds.

Additional funds were provided by the state of Pennsylvania and Susquehanna Area Regional Airport Authority, which owns and operates MDT and three other small airports.

General contractor KC Construction Inc. started work in November 2019 and completed the project in June 2020, nearly six months ahead of schedule.

Urban Engineers Inc., the firm that designed the project years before, provided final design, bid-phase services, environmental permitting, FAA coordination and construction management services. Navarro & Wright Consulting Engineers Inc. performed materials testing, surveying and additional inspection services as a sub-consultant to Urban.

Building Blocks

The levee was built in 1958 when the airport, then a U.S. Air Force support base, needed a longer runway to handle larger aircraft including B-47 and B-52 bombers. To gain enough space for the runway, engineers extended the shoreline farther into the river, which required adding a protective levee as well.   

Dave Spaulding, deputy director of engineering and planning for the regional airport authority, notes that the method selected to rehab the aging levee is somewhat unconventional. Instead of using riprap, or large rocks, to armor the levee, engineers specified mats of articulated concrete block for stabilization and erosion control.

Overall, the project design called for 1 million square feet of articulated concrete block mats. Though they vary in size, a typical mat used on the project measured about 8 x 21 feet and weighed roughly 6,600 pounds.

The mats, supplied by Contech Engineered Solutions LLC, are hand-strung together by a continuous loop of 3/8-inch high-strength nylon rope.

During the project, crews installed about 6,700 mats, sometimes 130 to 140 a day. “We believe this is the largest ACB (articulated concrete block) project in the country,” says Bobby Machiesky, on-site project manager/superintendent for KC Construction.

Spaulding reports that the concrete block mats proved to be more cost-effective and easier to install than riprap. They also are more effective at preventing erosion and controlling vegetation growth and damage from burrowing animals, he adds.

The life expectancy for the mats is about 50 years.

Layer by Layer

There was more to rehabbing the levee than installing concrete block mats.

First, crews had to restore a riprap road along the “toe” of the levee, adjacent to the river, to provide access for excavators, trucks and other equipment. Then, they removed all vegetation and applied a herbicide to ensure that no live growth remained.

“We didn’t want the contractor to have to remove large root balls that would impact the integrity of the levee or cause more erosion,” explains Brian Peda, deputy practice leader/construction engineer for Urban Engineers. “There was so much vegetation that it was like a forest in some spots.”

With the thick vegetation cleared, workers laid down a felt-like geotextile fabric to promote water drainage and prevent erosion and plant growth. That, in turn, was covered with a 4- to 6-inch base layer of about 1½-inch stone to further aid drainage. 

Next, crews installed a mesh geogrid with square 1/4-inch openings to reinforce and stabilize the stone layer. “Without that geogrid material, the stone could wash out during a high-water event,” Machiesky explains.

After the geogrid layer was in place, the heavy lifting began.

Crews used a large excavator with spreader-bar attachments to set the concrete block mats on top of the geogrid. After a few mats were in place, workers placed concrete into the horizontal gaps between them, effectively grouting the mats together.

Next, crews used a skid-steer loader outfitted with a cylindrical broom attachment to fill the cinderblock openings and the vertical gaps between mats with the same kind of stone used in the base layer. Peda likens this step to brushing in sand between paver blocks when building a patio. “You’re packing all that stone into open voids to further lock in the concrete blocks,” he explains.

KC Construction opted to begin laying concrete block mats at the bottom of the levee and work upward to get out of potential high-water zones as quickly as possible.

To set the bottom row of mats firmly in place, the contractor dug a 3-foot-deep anchor trench at the bottom of the levee and filled it with concrete to ground level. That formed a solid base that will prevent the heavy mats from moving down onto the toe of the levee, notes Machiesky.

Exacting Standards

The contractor used a concrete mix designed to withstand 4,500 pounds per square inch of pressure after it cures for 28 days. To ensure the strength and integrity of the concrete, workers filled eight cylindrical molds—6 inches in diameter and about 12 inches long—every time they poured 50 cubic yards of concrete.

Each time, six of the eight cylinders were taken to a lab, where they were load tested in a hydraulic press after curing for 28 days. The other two remained on site for 28 days of field curing. If any cylinders failed the load test, crews were required to remove and replace the associated concrete.

“We had no low breaks in the 3,000 yards of concrete we poured on site,” Machiesky reports, noting that the company records every concrete placement using real-time, kinetic-positioning GPS equipment, made by Topcon Positioning Systems Inc., to track pour areas and their corresponding test samples.

Overall, the project also required 24,000 cubic yards of riprap to build the access road, and 22,000 cubic yards of stone to build the base layer and fill holes in the cement blocks and voids between the blocks and mats.

Working on the sloped face of the levee was a job for experienced equipment operators, and not for the faint of heart. The structure is about 30 feet tall when measured from the average river level, and the grade of the slope ranges from 33% to 50%. The top of the levee is only about 12 feet wide.

“Sitting on that slope with a 100,000-pound excavator while picking up a 6,600-pound mat at that angle is difficult,” Machiesky emphasizes. “The further you ‘boom out’ to lay the mats down, the riskier it gets.”

Critical Communication

Construction crews had to communicate frequently with air traffic controllers, especially when working in or passing through restricted areas where their equipment could interfere with the localizer and glide slope systems. As such, the primary areas of concern were the access points at both ends of the 10,000-foot runway.

On days when visual flight rules were in effect, crews were allowed to take equipment near the restricted area when necessary. But if cloud cover or rain moved in, crews had to vacate those areas quickly to avoid affecting the navigational aid equipment—no easy task with excavators that only travel a few miles per hour.

“That happened three or four times,” Machiesky recalls, adding that the project generally enjoyed good weather.

Edwards notes that the project team planned the work near navigational aids only when clear skies were predicted.

“We’ve worked on smaller airports before,” adds Machiesky. “But nothing on this scale, with such a large runway and such big jets landing and taking off.”

In 2020, MDT logged 37,720 aircraft operations. It is served by five airlines, including American Airlines, Delta Air Lines and United Airlines, and primarily handles various commercial-service airliners and several wide-body cargo aircraft.

The runway as a whole was not closed during the project, but 393 feet on the south end was closed for five days to allow workers to install articulated concrete block mats at the top of the levee where it wraps around the end of the runway.

“That limited the amount of takeoff run available, but it didn’t deter any air traffic,” says Spaulding.

Keys to Success

Airport authority officials credit Fred Testa, MDT’s former airport director, for initiating the levee rehab, and Tim Edwards, its current executive director, for his proactive move to secure funding.

“Without their efforts, this never would have happened,” says Spaulding. “A big part of our success here was having a levee design on the shelf, ready to go in the event that funding became available. The window of opportunity for submitting a grant application was very small, so having a project design ready for submission was huge.”

Spaulding also highlights the value of the comprehensive, daily communication and coordination that occurred among the FAA, Urban Engineers and KC Construction—especially when navigational aid equipment came into play.

“It was a very well-coordinated project,” agrees Edwards. “Both KC Construction and Urban Engineers really kept things on track. Sometimes you just get lucky with a contractor, and in this case, we were lucky to work with KC Construction. We’d never worked with them before, but they were wonderful—no delays or constant change orders.”

Peda notes that meeting with airport officials at the start and end of each week ensured that everyone knew what work was occurring and what areas of the project were affected. Urban Engineers also emailed a map to key stakeholders every evening, outlining the location of the next day’s work.

“That way, we didn’t have to call, say, 10 people every day,” he explains. “We received a lot of positive feedback for that approach.

“Overall, on a scale of one to 10, I’d give the project a 10,” he adds. “Everything went pretty smoothly and according to plan.”

Subcategory: 
Environmental

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