Experimental Evaluation of Fiber Reinforced Polymer Piles in Load-Bearing Applications

This study was conducted to evaluate the performance of fiber reinforced polymer (FRP) piles in load-bearing applications for the Maine Department of Transportation, with the purpose of assessing pile strength, drivability, and durability. FRP piles were driven at a site between Richmond and Dresden, ME along the Kennebec River with dense glacial soils including cobbles and boulders. These piles were 12.2 m (40ft) in length with a nominal diameter of 610 mm (24 in) and manufactured using a [0/45/90/- 45] degree stitched E-glass fabric and a polyester resin. Piles were tested as concretefilled samples with 4layers of reinforcing fabric and a nominal thickness of 12.7 mm (0.5 in) or hollow samples with 8 layers of reinforcing fabric and a nominal thickness of25.4 mm (1 in). One of the hollow piles had a 1.22 m (4ft) concrete plug cast at its toe prior to pile driving. A Delmag D36-32 open ended diesel hammer with a maximum rated energy of 123 kN-m (90,560 ft-lbs) was used to drive piles to a target capacity of2670 kN (600 kips). After driving, piles were extracted to document damage and evaluate residual properties using flexural and axial compression tests. During driving, piles experienced varying levels of damage. Hollow piles exhibited a brooming failure at the head and the toe after encountering hard driving. The pile with a concrete plug at its toe experienced less severe damage at its toe than the hollow piles. The concrete-filled pile did not show signs of damage in the field, but the concrete-FRP bond failed during flexural testing. All piles achieved a geotechnical capacity over 1 780 kN ( 400 kips). Driven and extracted piles were brought to the University of Maine Advanced Structures and Composites Center to be tested in flexure and compared with undriven and load-cycled piles. Driving and cyclic loading did not appear to affect the stiffness of concrete-filled or hollow piles. There was no apparent loss in capacity due to driving or cyclic loading, but trends were ultimately inconclusive due to the small sample size and scatter of the data. Both piles that received hammer blows while filled with concrete lost composite action during flexural testing, indicating that additional reinforcement may be required for driving concrete-filled FRP piles. Driven and undriven pile sections were also proof loaded in axial compression to 4450 kN (1000 kips). Hollow piles did not show any change in behavior due to driving, but trends in the concrete-filled piles were inconclusive due to differences in concrete age. Mechanical and geotechnical properties of the FRP material were examined using flat FRP plates with 2 layers of reinforcing fabric and a nominal thickness of 6.4 mm (0.25 in). This testing established compressive, tensile, and shear properties along with interface friction values using three different granular soils (Ottawa sand, MaineDOT Type B aggregate backfill, and glacial till) at two different relative densities (50% and 75%). The FRP material was tested to verify compliance with the American Association of State Highway and Transportation Officials Guide Specification for Design of Bonded FRP Systems for Repair and Strengthening of Concrete Bride Elements [ 1] durability requirements. The material did not meet minimum property retention requirements