Macro Enterprises completed the design and installation of a sheeting and underpinning system for a 35-foot-deep excavation for a new underground parking garage at New York Hospital Queens. The sheeting system consisted of steel soldier piles, timber lagging and earth tiebacks. Soldier piles were installed without impact noise or vibrations by advancing a continuous-flight hollow-shaft auger into the ground for the full length of the soldier pile. A self-hardening slurry was pumped through the hollow shaft to hold the hole open while the auger was being withdrawn. The soldier pile was lowered into the slurried hole. After the slurry hardened, timber lagging and grouted earth tie-backs were installed to resist the lateral earth pressures as the excavation proceeded.
Concrete underpinning was preformed using alternate pit sequencing. The underpinning was constructed using two lifts due to the difficulty of excavating large boulders and cobbles that were encountered in the sheeted pits. Sheeted pits were hand-excavated to 20 feet deep for the first lift. Reinforcing steel was installed and concrete was poured. Steel plates, wedges and drypack were used to transfer building loads onto underpinning. Earth tiebacks of 100 kip capacity were drilled tested and locked-off to provide lateral support of the underpinning as the excavation proceeded to the bottom of the first lift of underpinning. The entire underpinning and tieback procedure was repeated to advance the underpinning to the required subgrade elevation.
Macro Enterprises Ltd. is a specialty pile driving, drilling, shoring and underpinning contractor doing business in New York since 1977, offering complete design/build services for sheeting, shoring, underpinning and tieback drilling.
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