Addressing the rapid deterioration of timber piles supporting New York City waterfront structures exacerbated by the return to New York Harbor of marine
Jim Williams
Addressing the rapid deterioration of timber piles supporting New York City waterfront structures Û exacerbated by the return to New York Harbor of marine borers Û New York City Economic Development Corporation (NYCEDC) developed a waterfront management and rehabilitation program for its piers and wharves. Refurbishment and stabilization of the 60-plus-year-old, 845-ft.-long St. George Fishing Pier, part of the Staten Island Ferry Terminals redevelopment, would require below-deck timber pile encasement due to years of extreme marine erosion.
Retained by Turner Construction on behalf of NYCEDC to determine the scope of restoration, Engineering (Pound Ridge, N.Y.) specified 121, 20-ft.-long, stay-in-place, fiber-reinforced-polymer (FRP) pile jackets filled with lightweight concrete. Pennmax principal John Pensiero notes, As the most critical performance spec was durability to extend service life of the concrete, we chose a stay-in-place form to provide additional durability, protection, and economic efficiencies, since no stripping was required. We also specified a ∫-in. form thickness [versus ?-in. standard] to withstand ice/debris impact forces and prevent concrete erosion from tidal action. Accordingly, Independence, Kan.-based Molded Fiber Glass Construction Products (MFG-CP) was enlisted to provide FRP pile jackets, and Trevcon Construction Co. was selected to perform underwater construction.
MFG-CP met Pennmax’s performance specs by supplying a single-seam FRP solution. The forms’ superior structural strength is attributed by their manufacturer to component materials, including chop strand mat and woven roving, which provide resistance to abrasion while adding structural stability and impact resistance with proper placement of concrete or grout. Further, the 30-in.-diameter forms are durable in seawater and chemically resistant to acids, alkalis and most solvents. According to Pensiero, Because the forms extend up 20-plus feet and would initially contain fluid concrete, they had to be strong enough to endure concrete pumping operations. The pile forms’ thickness and tensile strength ensured that they wouldn’t blow out during the pour.
Lightweight and relatively easy to install, the manufacturer affirms, MFG-CP pile jackets feature a slip-joint/tongue-and-groove closure configuration to facilitate underwater assembly. Additionally, a flexible, peal-away liner seam design and resin bond finish eliminate the need to sand-blast for chemical adhesion in conjunction with pumping operations. Due to their 20-ft. extension in deeper water, the jackets incorporated a bell-and-spigot connection, saving installation time and allowing stacking, besides adding structural strength for concrete placement.
Trevcon Project Manager Ron Treveloni, Jr., reports, Installation began by placing steel reinforcing around the existing pile, which 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. A single diver then installed each form with the assistance of two dock builders, fastening each pile’s tongue-and-groove configuration in place.
Regarding the project’s unconventional concrete pour, Treveloni observes, We utilized a concrete pump at the bulkhead, since no concrete trucks were allowed on the pier. Hard pipe extending about the length of a football field from the land pumped to a hose on the pier, then down to the diver at the base of the pile. The pumping pushed concrete from the bottom up at three yards per pile. Through two pumping ports on each pile Û one on the bottom and one in middle Û each unit was poured in two lifts, taking about one-half hour per pile. Utilizing a 3/8-in. lightweight stone concrete was tricky, according to the project manager, but mandatory, because the additional weight could pose potential structural damage to the pier.
Given the correct epoxy/concrete bond, FRP jacket forms effectively encase existing timber, steel, or concrete piles to rehabilitate them to original or better strength. Û Jim Williams at MFG Construction Products, [email protected], 800/225-5634