Underwater Piles

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The first application of PileMedic™ for repair of underwater piles was recently completed at Guilford House Condominiums, Bay Harbor Islands, Florida (Fig. 3). The project is located on the environmentally sensitive South Florida intra-coastal waterway. Approval from the Florida Department of Environmental Protection DEP was required prior to restoration.

The 14-inch x 14-inch piles (Fig. 4a) had substantial steel corrosion and spalled concrete. There was no original design or repair methodology. The contractor, CSI, recommended using the new system for the piles that supported an overlook on the pool deck. Use of conventional pile jackets was contemplated. However, the contractor chose the PileMedic™ system for ease of installation and the added structural enhancement.

The laminates were packaged in 4-ft wide x 300-ft long rolls. The manufacturer’s specification requires a minimum double-layer wrap plus an 8-inch overlap beyond the starting point. This reduces the inter-laminar shear stresses between the two plies of PileMedic™ and ensures that the pile is confined by two plies of laminates all around, i.e. 360⁰. Unlike the jackets shown in Fig. 1, this system leaves no plane of weakness along the height of the jacket.

For this application, it was decided to encase the piles in 21-inch diameter cylindrical shells; this was a tightly fitting circle that would leave a small gap (about ½ inch) between the jacket and the pile at the four corners of the piles. The circumference of such shell is 66 inches. Thus, the laminates were cut into 66+66+8= 140 inch long pieces. This allowed for creating a two-ply cylindrical shell with a diameter of approximately 21 inches plus an 8-inch overlap at the end.

The two-component epoxy supplied by the manufacturer is environmentally safe and complies with the highly stringent requirements for lining potable water pipes. The epoxy is also moisture-insensitive and it cures under water, eliminating the need for any coffer dams. The epoxy was mixed using a jiffy mixer and it was applied with a thickness of 40 mil to the 66+8=74 inch length of the laminate; the first 66 inch length of the laminate that will be placed next to the pile does not need to be coated with epoxy (Fig. 4b).

Since the water was relatively shallow, the workers could pick up the laminate and walk it in water. At this time the laminate is wrapped around the pile to create the 21-inch diameter shell (Fig. 4c). At this stage, the uncured epoxy coating serves as a lubricant allowing the laminate to slide easily as the crew makes final adjustments to the diameter of the shell. Ratchet straps were used to fix the diameter of the shell and prevent it from unraveling before the epoxy cures (Fig. 4d). The cylindrical shell can be moved vertically along the height of the pile to its final position. In this case, it was pushed down into the mud to create a seal at the base.

An underwater grout was mixed and pumped with a hose into the annular space between the jacket and the pile (Fig. 4e). As the tremie mix rose to the top, it displaced the water in the annular space until the entire annular space was filled with grout. At this stage, the hydrostatic pressure of the grout pushes the two layers of the PileMedic™ jacket tightly against one another while the ratchet straps prevent the jacket from opening up. At the same time, the heat generated from the hydration process of the grout helps with the curing of the epoxy. Depending on the ambient temperature, the epoxy will cure in several hours at which time the ratchet straps can be removed. The repaired piles at the conclusion of the project are shown in Fig. 4f.

In repair of underwater piles, it is common to schedule the work around low tide hours and working continuous 8-hour shifts may not be efficient. Nevertheless, on this project, the repair of fourteen piles was completed in 4 working days using a 3 man crew.