During the 2012 Hurricane Sandy event, the Bay Park Sewage Treatment Plant in Long Island, NJ, was inundated with several feet of storm surge. Millions of gallons of sewage were released into the adjacent waterway, which connects via other small waterways to the Atlantic Ocean. In 2014, FEMA funding was allocated for rehabilitation of the plant, including construction of a perimeter flood control system. Moretrench was contracted to install ACIP pile foundations, install a vibrated beam slurry wall cut-off barrier, and perform jet grouting where the cut-off could not be constructed due to the presence of the large underground utilities.
Due to property line constraints around certain areas around the site, three different wall sections were designed by the joint venture of Arcadis/Hazen & Sawyer Engineers to complete the flood protection wall. The primary design consisted of an earthen levee with a central clay core and a vibrated beam subsurface cut-off trench. Where insufficient space was available for leeve construction, a pile-supported T-wall was incorporated. The treatment plant remained in operation throughout flood control installation.
Pile Foundation System
The T-wall section consisted of a double row of 24-inch 4,000 psi auger cast piles reinforced with either #8 or #11 reinforcement cages. Moretrench successfully conducted compression load tests on 90-ton and 70-ton capacity production piles to 238% of working load to verify design assumptions. In total, 799piles were installed to varying tip elections and constructed using over 3,000 cubic yards of pile grout.
Vibrated Beam Cut-off Wall
The advantages of a thin(5-inch) vibrated beam cut-off for this particular project included the very limited impact on the site, the small footprint of the mixing plant, and that it could readily be installed through the myriad auger cast piles supporting the T-wall.
To create the cut-off, Moretrench utilized a large telescopic mast drill rig to vibrate a W33x152 beam into the ground. The face of the beam was fitted with a guide shoe to ensure that each penetration was continuous with the previous one. During driving and extraction of the beam, a self-hardening slurry engineered to be compatible for use in the brackish conditions was pumped through the shoe to fill the void created. In the areas where the T-wall was constructed, a short HDPE membrane was embedded on the top of the wall and connected to the T-wall concrete footing to ensure continuity. Viscosity and mud weight were tested every 20 LF, and samples were cast and laboratory testing performed for every 750 LF of wall. Over 6,700 LF of trench was installed to a tip elevation of -25 for a total vertical area of 218,000 ft2.
To achieve the required closure, Moretrench utilized double-fluid jet grouting to install a 4- to 6-inch thick jet grout panel at each approximately 20-ft location, extending to a tip elevation of -25. Spoil generated by the grouting operation was pumped into above-ground pits, allowed to set up overnight, and trucked off site. Verification testing measures for the jet grouting operation included retrieval and casting of neat grout and spoil samples for 7- and 28- day unconfined compressive strength (UCS) and permeability laboratory testing. Results verified that all requirements had been met.
Key to the smooth completion of jet grouting operations was Moretrench's use of its mobile jetting system that allowed the multiple locations to be addressed in a timely and efficient manner.