High Capacity Drilled Piles in Brooklyn-Paper

Paper

Pdf Summary

The Pacific Park development in Brooklyn requires foundations for high-rise buildings on a platform above an operating Long Island Rail Road yard. Because the yard is congested and must remain in service, the design team selected high-capacity drilled piles alongside spread footings and small mats, rather than a massive mat spanning the rail yard.<br /><br />The site is underlain by glacial sands and gravels, generally dense to very dense but containing cobbles and boulders that complicate drilling. Two pile sizes were used: 13⅜-inch piles designed for capacities up to about 295 tons and 24-inch piles designed for 600 tons. Piles had bond zones roughly 50–65 feet long and were installed using combinations of roller bits and down-the-hole (DTH) hammers, then grouted.<br /><br />Static compression tests included two 24-inch piles tested to 1,200 tons and six 13⅜-inch piles tested to 520–560 tons. Additional testing of tiedowns and soil anchors helped establish allowable bond stresses. With a factor of safety of 2, test results supported allowable bond stresses of about 20 psi for the smaller piles, 25 psi for the 24-inch piles, and up to 30 psi for soil anchors. Tiedown results were lower, partly because their bond lengths were conservatively designed.<br /><br />The study found that DTH hammer installation was feasible, though performance depended substantially on equipment, methods, and pile size; ground disturbance, caving, and occasional low capacities occurred. Roller-bit approaches were also challenged by the abundant obstructions. Overall, field testing validated cost-effective, high-capacity foundations for the constrained site and showed that drilled-in elements could achieve reliable bond resistance in Brooklyn’s glacial soils.

Keywords

Pacific Park Brooklyn

high-rise foundations

Long Island Rail Road yard

drilled piles

spread footings

glacial sands and gravels

down-the-hole hammers

static compression tests

bond stress

soil anchors