30 Hudson Street Foundation Design and Construction in Variable Rock

Collaboration, cooperation and - borrowing a phrase from hockey - "changes on the fly" are all aspects that came to mind in the construction of the 30 Hudson Street tower. A former industrial site on the west shore of the Hudson River, offering spectacular views of lower Manhattan, was chosen for the location of this office tower. Available information indicated the presence of multiple existing founda- tions, miscellaneous and potentially contaminated fill, and rock-filled timber bulkheads. The subsurface profile consisted of fill over river bottom organic silt, compact sand and rock at depths varying from 30-55 ft (9-17 m). Existing boring data, some of which dated back as early as 1902, did not include sampling details, nor were precise sampling locations easily. determined. Mueser Rutledge Consulting Engi- neers attended early design discussions with the owner and the rest of the design team and provided foundation alternatives for the following three schemes: . • . No basement with multiple parking levels above grade A shallow basement, still requiring above grade parking A deep basement for all parking, with the most notable functional aspect of keeping the lobby level at grade Due to the presence of known obstruc- tions, a deep seam of decomposed rock, possible contaminants and the neces- sity for deep foundations into rock (for no or shallow basement), the deep basement scheme with a perimeter diaphragm (slurry) wall was selected as the preferred alternative. Although it had a higher installation cost, it pro- vided the owner with many benefits such as below-grade parking, building the lobby at the ground floor level, removal of contaminated soil and the potential for future expansion within the diaphragm wall. The contractor, in consultation with our team, chose to pre-trench the perimeter wall alignment to a depth of about 10 ft (3 m) with a low strength concrete slurry mix, which aided in the removal of obstructions and pro- vided a permanent wall that wouldn't have major intrusions into the site owing to the volume of the removed obstructions.