North Carolina’s coastline is one of the most vulnerable for a direct hurricane strike facing the Atlantic Ocean due to its protruded coastline. Factor in low-lying land, the Lumber, Pee Dee, and Cape Fear rivers, and the potential of catastrophic flooding is very high. In 2016, Hurricane Matthew stalled across the region keeping inland waterways above flood levels for weeks. Less than two years later, Hurricane Florence struck southeast North Carolina dumping more than 25 inches of rain. As a result, multiple Duke Energy substations were inundated with flood water, and power to much of the region was out. Technicians were unable to begin making repairs until the water receded. This left substations down for more than five weeks, leaving thousands of Carolina residents without power.
Having faced a pair of “Storms of the Century” in two years, Duke Energy had to quickly develop a solution to protect their substations from flooding prior to the height of the upcoming hurricane season. After failed attempts to raise the substations and construct temporary flood walls, which were destroyed by Hurricane Florence, Duke Energy needed to implement a permanent solution – and do it within a tight timeline.
Duke Energy ultimately selected CMI for their ability to meet two major criteria: long-term weatherability and project schedule. UltraComposite® FRP and ShoreGuard® PVC Vinyl Sheet Piles were specified due to the material’s operating lifespan, non-conductivity, environmental sustainability, and lower total cost of ownership compared to steel or concrete. Duke Energy was able to establish aggressive installation schedules with guaranteed project pricing, leveraging CMI’s capacity management program and stable supply chains.
“We were looking for a flood wall and seepage barrier that would give us adequate protection but at the same time have low maintenance and have longevity,” said Charlie Sandifer, regional engineer for Duke Energy’s southern district. “Our desire is to stay ahead of the floodwaters.”
Ryan Mosier, Duke Energy Corporate Communications Director, emphasized the thorough research and nationwide exploration undertaken by Duke Energy, citing a visit to the Atlantic County Utilities Authority (ACUA) wastewater treatment plant and wind and solar farm in Atlantic City, NJ. The ACUA project, featuring a 4,896 linear foot flood wall constructed with CMI’s UC-95 UltraComposite (FRP) Sheet Piling, served as an influential reference. Duke Energy adopted the same equipment and methods, utilizing CMI’s PileClaw® Steel Mandrel to drive the UltraComposite sheets into the ground for their seven substations.
Sheet pile installation began in June 2020 and each of the seven sites presented its own challenges. Gary Greene Engineers, with assistance from CMI’s Engineering department, was the lead engineer on the project. Construction was completed by HEPACO, Langston, and Cianbro. ShoreGuard 950, UltraComposite 50, and UltraComposite 75 synthetic sheet pile profiles were ultimately chosen based on site-specific soil parameters and varying flood wall height design requirements. The seven flood walls extend six to eight feet above grade at each site and the sheets were driven to varying depths utilizing CMI’s PileClaw mandrel to drive the sheets accurately and increase daily production. The relative lightweight SG-950, UC-50, and UC-75 sheet piles proved pivotal in meeting the demands of installing sheet pile in tight spaces around the seven substations. Removable aluminum gates allow crews access to the sites and can be quickly installed ahead of any forecasted flooding. TimberGuard® walers were installed at the top and each side of the flood walls to add strength.
Duke Energy determined the substations would need a permanent sheet pile wall that would keep flood waters out and block seepage. Steel sheet pile was initially considered but quickly dismissed due to the inherent volatility in steel prices, installation costs, and safety concerns. Additionally, the susceptibility of steel to corrosion in highly charged environments played a pivotal role in Duke Energy selecting CMI’s UltraComposite FRP Sheet Pile and ShoreGuard PVC Vinyl Sheet Pile to protect their flood-prone substations.
CMI’s Engineering department worked with a team of Duke engineers and local engineer, Gary Greene PE, to provide calculation packages for each of the seven substation flood walls. The design guidelines were based on the USACE’s Design Guide for I-Walls along with the USACE’s latest Engineering Manual for Flood Walls.
After dealing with two catastrophic “Storms of the Century”, resulting in millions of dollars of damage, loss of life, and extended periods of power outages, the Carolinas are now more prepared when the next hurricane or flood event strike the coast.
