Seawall Construction with GFRP Bars

Introduction
  • In 2016, Flagler Beach, FL, was severely impacted by Hurricane Matthew.
  • A secant-pile seawall is under construction to mitigate future storm impacts.
  • The seawall will be approximately 1.5 km (nearly 5000 ft) long and utilizes glass-fiber-reinforced polymer (GFRP) bars as reinforcement.
Project Background
  • SR A1A Importance: Designated evacuation route but vulnerable to storm surges.
  • Existing infrastructure, including steel sheet piles, suffered corrosion and erosion, leading to failure during Hurricane Matthew.
  • The new seawall aims to support the highway if sand dunes get eroded during major storms.
  • The project includes dune reestablishment to maintain the local environment's character.
Specifications and Standards
  • Project Standards: The design adheres to several specifications:
    • Florida Department of Transportation (FDOT) Structures Manual (2018)
    • AASHTO LRFD Bridge Design Specifications
    • ACI 440.1R-15 for structural concrete with FRP bars.
  • Concrete Requirements:
    • Class IV concrete without silica fume with a 28-day compressive strength of 5500 psi (38 MPa).
    • Grout must have a minimum flow rate of 15 seconds and compressive strength of 4000 psi (28 MPa).
  • Environmental Considerations: The design accounts for a harsh marine environment, requiring a minimum resistivity of 300 Ω·cm due to high chlorides (1320 ppm).
GFRP Properties and Testing
  • Laboratory Testing: Conducted at the University of Miami's Advanced Structures and Materials Laboratory:
    • Tests confirmed GFRP bars exceed FDOT specifications for cure, glass transition temperature, fiber content, moisture absorption, and tensile properties.
  • GFRP Characteristics:
    • High tensile strength (approximately twice that of steel)
    • Low weight (about one quarter of steel)
    • Non-corrosive, which contributes to minimal maintenance costs.
Seawall Construction Details
  • Piles:
    • Auger-cast piles, 36 in. (910 mm) in diameter.
    • Primary piles (36 ft) reinforced with 25 No. 8 GFRP bars, secondary piles (20 ft) with a single bar.
  • Construction Sequence:
    • Uses a guide wall for aligning and defining pile locations.
    • Installation took 4.5 months, with 1847 piles installed using a rotating sequence.
    • Primary and secondary piles interlock, ensuring homogeneity in foundation walls.
  • Installation Efficiency:
    • GFRP cages resulted in 32-52% time savings compared to steel reinforcement in typical projects.
Environmental and Aesthetic Impact
  • Completed seawall construction includes a dune to mitigate scouring and preserve environmental aesthetics.
  • A variety of environmental considerations ensured the seawall blends with the local landscape, maintaining the area's “Old Florida” feeling.
Final Thoughts
  • As GFRP technology continues to evolve, its integration into projects emphasizes durability and cost-effectiveness while addressing environmental impacts.
  • Ongoing collaboration among various engineering and construction entities is pivotal for project success.