Project Florida Power & Light St. Lucie Nuclear Power Plant channel protection Design Consultant Greenman-Pedersen, Inc. Contractor/subcontractors Underwater Engineering Services, Inc. Florida Dredge & Dock Blue Goose Construction Product application ArmorFlex articulated concrete block revetment provides protection from storm-induced erosion along cooling water intake and discharge canals for a nuclear power plant on Florida’s Atlantic coast.

Hurricane damage leads to hard-armor solution for channel repair.

During the 2004 and 2005 storm seasons, hurricanes devastated some U.S. Atlantic shorelines. Hutchinson Island, a barrier island on the coast of Florida’s Martin and St. Lucie Counties is home to the St. Lucie Nuclear Power Plant, operated by Florida Power & Light (FPL). The plant has been in operation for approximately 40 years, and its 1-mile-long, horseshoe-shaped, cooling water intake and discharge canal runs from the plant to the Atlantic Ocean. Hurricanes striking the area took their toll, causing severe erosion to the canal embankments.

Conventional repair methods would have required shutting down the plant, drying out the canals, and performing the repairs. FPL wanted a repair method that could be implemented with the plant units running. Options for the canal repair included stone, rip rap, cast-in-place concrete, and other heavy-duty conventional erosion control means.

FPL decided to request design-build proposals that incorporated an ArmorFlex concrete revetment system installed while the plant was in operation. The ArmorFlex system is a flexible, interlocking matrix of machine-compressed, cellular concrete blocks of uniform size, shape, and weight. The matrix is then connected by a series of polyester rope cables, which pass longitudinally through preformed ducts in each block and provide articulation between the adjacent blocks. Blocks are designed with beveled side walls to allow for flexibility in all directions.

Articulated concrete block revetments are being placed along the 1-mile-long cooling water intake and discharge canals at Florida Power & Light’s St. Lucie Nuclear Power Plant to protect the embankments from damage caused by hurricanes and severe storms.

During the bidding and evaluation process, CONTECH Construction Products Inc. submitted an extensive engineering proposal to Babylon, N.Y.-based design consultant Greenman-Pedersen Inc. (GPI) on the ArmorFlex product. The proposal included reports of wave testing conducted at Delft Hydraulic Lab in the Netherlands, overtopping flow analysis conducted by the Federal Highway Administration, and tests on hydraulic stability during overtopping flow conducted at Colorado State University. The ability of the system to resist the forces of wave action and the effect of the drainage layer were important considerations in the selection process.

FPL relied on several factors—experience, work approach, materials, applications, and overall team competency—to select the contractor, Underwater Engineering Services, Inc. (UESI), of Port St. Lucie, Fla. UESI, along with GPI, selected subcontractors Sims Crane, Tampa, Fla.; Blue Goose Construction, Ft. Pierce, Fla.; and Florida Dredge and Dock, Tarpon Springs, Fla., to win the project based largely on best proposal and product experience. The proposal highlighted UESI’s extensive experience with installing ArmorFlex systems, including the large installation at FPL’s Sanford power plant canals, as well as its ability to provide an innovative approach to challenging project requirements.

Engineering, design, and installation
UESI used the engineering services of CONTECH Construction Product’s internal design team for the design-build project. The project specification called for changing design criteria as a function of where the articulated concrete blocks (ACBs) were to be installed and what forces were acting on them at that specific area. In general throughout the project, revetment was designed according to two primary forms of analysis—hydraulic stability for overturning and wave attack.

For below water placement, dive crews direct the crane operator and help guide the mats into place.

The first form of analysis determined the factor of safety for hydraulic stability. This analysis was done with regard to project geometry, velocity, and shear values set forth by the project specification. The stability analysis was performed according to industry standards for articulated block. Secondly, wave attack analysis was performed according to the Pilarczyk Method for articulated block systems. As expected when investigating wave attack—typically more stringent of the two forms of analysis—the wave attack conditions defined the block thicknesses selected for this project.

UESI had previously completed many large-scale projects using ACB mats, but had some unique problems to overcome at the St. Lucie Nuclear Power Plant. The canal revetment involved placement and precise grading of a drainage layer made with #57 stone sandwiched between layers of geotextile fabric. This would provide the optimal revetment design and high protection from wave attack.

"This project is unique in itself in that there are many obstacles to either work around or temporarily remove on the embankment slope," said Dean Reynolds, UESI project manager. "Part of the intake canal is fenced, and FPL requested that the repair be implemented without affecting the fence. This has made one part of the intake canal inaccessible to the typical equipment used for a repair such as this."

The 30-foot-deep canals have an embankment length of approximately 150 feet. Of that, 100 feet is underwater. UESI planned for its subcontractor, BGC, to use excavators placed on sectional barges to provide access and minimize turbidity (an important consideration to FPL plant operations) during construction. Additionally, excavators are using a GPS system with a cab-mounted screen that allows the operator to see where his bucket is in relation to the required grade. The grade is provided in electronic format and is loaded into the GPS equipment.

The barge-mounted excavators can grade accurately to a depth of 30 feet but could not accommodate the volume of material that had accumulated and washed down to the bottom of the intake canal. UESI extensively researched specialty dredges and found that Florida Dredge & Dock had a dredging vessel suitable for this application. Its variable-length cutter head suction dredge can remove the large volumes of material that had accumulated in many places along the intake canal bottom.

Channel revetment at the plant began in January 2008. UESI estimates that approximately 1.3 million square feet of ArmorFlex ACB mats and 1.7 million square feet of geotextile fabric will be used. The St. Lucie Plant canals represent approximately a 1-mile-long work area. The large-scale project includes extensive cut-and-fill embankment work and working around embankment obstacles, with the majority of installation work being done underwater. UESI planners have used comprehensive and detailed work plans to keep the project ahead of schedule through uniquely configured areas.

ArmorFlex mats arrive on site on flat bed trucks as a system of pre-assembled mats and are lifted with a spreader bar for placement. For the intake canal, UESI is using a 250-ton crane to maneuver the 16,000-pound ACB mats, which are staged ahead of the placement crane by a smaller crane. Geotextile (filter fabric) is placed by UESI dive crews using a series of weights and pipes that keep the fabric on the subgrade, especially in the underwater area, which experiences 1-foot-per-second (fps) current.

ACB mats are lifted by crane in accordance with specific lifting and rigging plans and placed as far as 175 feet from the crane location. As the ACB mats are placed into the water, dive crews direct the crane operator and two divers work together to help guide the mats into place. Four, 38-foot-long mats cover the embankment from bottom to top.

UESI and CONTECH have been working together when field conditions have required expedited service or specialized mat sizes. The lateral seams between the four mats are filled with a 4,000-pounds-per-squre-inch concrete.

"The underwater seams feature concrete designed with special ’anti—washout’ admixtures that is pumped and placed by divers," said Graham Cover, UESI superintendent. "Despite having to contend with the current in the canal, the concrete mix has performed as designed with regard to segregation and lack of turbidity."

Once work commences in the discharge canal, UESI will work with a smaller barge-mounted crane and ferry ACB mats to the crane for placement. In the discharge canal, the UESI dive crew will encounter water temperatures that may reach 100 degrees (heat sink water from cooling the plant). Accordingly, UESI plans to use chiller units to pump chilled water through the divers’ suits to form a cool barrier to the hot water.

Environmental aspects
Canal water turbidity was a primary concern for FPL because excessive turbidity could foul plant condensers and affect operations and output. UESI addressed this concern during planning for all working operations. Work methods to place fill and grade underwater are being accomplished with excavators to reduce the distance materials travel through the water column. Since the ACB mats are precast, they can be placed without creating turbidity as well.

UESI is using two, moored sonde units supplied by Lockner Environmental to monitor turbidity upstream and downstream of work areas every 15 minutes and transmit the information to a website via cellular technology. The website monitors the data and sends text alerts to project personnel whenever preset turbidity levels are reached. This system allows crews to identify potential problems and react to them expeditiously, contributing to reduced labor costs and avoiding repetitive testing frequently required by manual systems.

Additionally, a comprehensive Spill Prevention and Refueling Plan was developed incorporating state-of-the-art equipment, measures, contingencies, and management.

Quality control and safety
FPL demands that contractors working at its St. Lucie Nuclear Power Plant meet the highest safety and quality standards. Early in the project, multi-beam sonar was used to perform bathymetric surveys and ensure that the subgrade was within specification requirements. Because of the amount of floating equipment and the space required to collect bathymetric data effectively, it became apparent it could not be done without affecting the construction. GPI had to change methods and use a GPS grade system mounted on a rod for data collection to verify grade conditions. In addition to the spot checks with the GPS system, GPI relies on UESI dive teams to perform visual inspections of the subgrade before any of the areas are approved for geotextile and ACB mat placement.

Teams from GPI and CONTECH work to make sure all documentation regarding manufacture of the mats is received, and they check quality on site prior to the mats being unloaded.

UESI’s safety program has also been managed effectively through comprehensive and detailed site safety and work plans. These plans, integrated with FPL safety requirements, include extensive training, daily meetings, human performance measures, and error-prevention methods. On a heavy construction project of this magnitude, these controls are in place to manage worker safety around heavy load lifts using crane and rigging, grading and excavation with heavy machinery, and marine vessel operations all integrated near an operating nuclear power plant.

The project is also unique in that it involves commercial diving. To provide additional perspective, the project, on a daily basis, typically logs 38 man-hours of diving time, with more than 700,000 pounds of ACB mats stockpiled or placed by crane.

Once complete, the canals are expected to operate more efficiently and have additional protection from future storms. The project, expected to be complete by November 2009, has been touted as one of the most unique of its kind in the world. More than 1.2 million square feet of mats will be placed during the next two years, making it the largest ArmorFlex project in CONTECH history.


Joe Frederickson is construction manager for Underwater Engineering Services, Inc., Port Saint Lucie, Fla. He can be contacted at jfrederickson@uesi.com.