The return of marine borers to New York Harbor has had devastating consequences to many of New York City's waterfront structures that are supported by fast deteriorating timber piles. In recent years, New York City Economic Development Corporation (NYCEDC) has responded by developing a waterfront management and rehabilitation program for its piers and wharves including the St. George Fishing Pier's Pier 1; just steps away from the Staten Island Ferry.

As part of their recent redevelopment of the Staten Island Ferry Terminals that connect with the southern tip of Manhattan, NYCEDC deemed that the 60+ year-old Saint George Fishing Pier required below deck timber pile rehabilitation/encasement due to years of extreme marine erosion. A key component of a larger renaissance of St. George's wharf, pier, and bulkhead properties, the refurbishment and stabilization of the 845-foot-long pier would ensure the continued opportunity for the public to catch bluefish, flounder, blackfish, porgy and striped bass from the shoreline that feeds into Upper New York Bay.

To determine the scope of restoration and most efficient construction solution, NYCEDC's construction manager Turner Construction of New York, N.Y., hired Pennmax Engineering of Pound Ridge, N.Y., to provide underwater inspection and bid documents for the repairs. Based on their assessment of encasement repairs required to prevent future deterioration and extend the life of the structure, Pennmax specified 121, 20-foot long, stay-in-place fiber-reinforced polymer (FRP) pile jackets that would be filled with lightweight concrete.

According to Pennmax's principal owner John Pensiero, the most critical performance spec was durability to extend the life-cycle integrity of the concrete.

"We chose a stay-in-place form to provide additional durability, protection, and economic efficiencies since no stripping was required," Pensiero said. "We also specified a quarter-inch form thickness to withstand ice/debris impact forces and prevent erosion of the concrete from tidal action."

Turner Construction and NYCEDC approved the Pennmax drawings for the project and then Turner procured Trevcon Construction Company Inc. of Liberty Conrer, N.J. to perform the underwater construction. Trevcon, in turn, selected Molded Fiber Glass Construction Products (MFG-CP) of Independence, Kan., to satisfy the project specifications for the FPR pile forms. Because of the underwater construction of the pile restoration; Pier 1 will remain open to the public during construction. The project began in October 2008 and is scheduled for completion this summer.

Pile Jacket Performance
To help restore the structural integrity to the deteriorating piles, MFG-CP, a division of Molded Fiber Glass Companies, met Penmax's performance specs in providing a structurally stronger single seam FRP solution designed to leave in place — which meant no removal assembly time.

Made from chop strand mat and woven roving, the two materials provide better physical properties so the jackets meet/exceed specifications vs. gun-roving/chopper gun applied which is not as strong. The resulting FRP composition benefits provide resistance to abrasion while adding structural stability and impact resistance when concrete or grout is properly placed in the form. Additionally, they are chemically resistant to acids, alkalis and most solvents and are durable in seawater.

The Pier 1/Pile Jacket specs include:

• Thickness: a quarter-inch thick vs. an eighth-inch standard
• Diameter: 30-inch
• Length: 20-foot
• Weight: 400 pounds. per form
  
  

"Because the forms extend up 20-plus feet and would initially contain fluid concrete, they had to be strong enough to endure the concrete pumping operations and prevent blow-out. MFG-CP's pile forms met the required thickness and tensile strength to ensure that they wouldn't blow-out during the pour," Pensiero said.

The MFG-CP pile jackets are lightweight and relatively easy to install; featuring a slip-joint/ tongue-and-groove closure configuration which makes underwater assembly easy for divers. The FRP pile jackets also offered a flexible, peal-away liner design seam and a resin bond finish to the jacket − eliminating the need to sandblast for chemical adhesion to work in conjunction with the lightweight stone concrete pour.

Due to the 20-foot extension of the jackets in deeper water, the jackets used a bell-and-spigot connection. This saves time in installation, allows for stacking and adds more strength structurally for concrete placement during the pumping operation.

According to Ron Treveloni Jr., Trevcon project manager, installation began by using steel reinforcing around the existing pile that was measured to fit the FRP form.

"Then three to four dock builders dropped each form in the water and set it on a floating platform to each pile location," Treveloni said. "A single diver then installs each form with the assistance of two dock builders; fastening each pile's tongue-and-groove configuration in place."
Treveloni noted the unique concrete pour processes.

"We used a concrete pump at the bulkhead because no concrete trucks were allowed on the pier," he said. "Hard pipe extending about the length of a football field from the land pumped to a hose on the pier, and then down to the diver at the base of the pile.

"The concrete pumping pushed from the bottom up at 3 yards per pile. There were two pumping ports on each pile − one on the bottom and one in middle. Each pile was poured in two lifts, taking about a half hour per pile."
Treveloni said they used a 3/8-inch lightweight stone concrete. "It's a tricky concrete, but it was mandatory because the additional weight could pose potential structural damage to the pier."

Conclusion
With the growing need for strengthening waterfront infrastructures including pile deterioration due to ice, marine borers, floating debris, chemical pollution, oils, acids, water and tidal pumping, there is an essential charge for alternative, cost-effective restoration solutions.

Combined with the correct epoxy/concrete bond, the FRP repair jacket forms surrounding existing piles, whether timber, steel or concrete, can efficiently refurbish instead of replacing the existing pile − t hus, strengthening them to their original or greater strength.

In addition to pile replacement savings, the MFG-CP jacket installation also accommodates the efficiency of requiring no pier, terminal or facility shut-downs. MFG-CP offers standard diameters available in 12-inch through 36-inch and can accommodate custom sizes for unique applications. Lengths are produced to specifications and ultraviolet resistance accommodations are available.

"MFG has been our choice of FRP pile jacket forms since we started this type of work," Treveloni said. "Not only have they given us quality products but their service and the ability to meet delivery dates is outstanding."