1 Seaport Residences, 161 Maiden Lane, was the first high-rise building in Manhattan constructed on a structural mat supported by ground improvement.
A 57-story high-rise building was to be constructed on a small parcel of land (approx. 5,000 sq. ft.) in lower Manhattan. The original foundation design of the Maiden Lane high-rise consisted of caissons drilled into bedrock found at significant depths. This solution was not only expensive but difficult to construct given the tight site logistics.
Ground conditions consisted of 25-30 ft of uncontrolled urban fill, including timber piles and old foundations, overlying a 5-15 ft thick layer of soft clay, silt, and peat. Natural sandy soils existed below the cohesive layer, with competent mica schist bedrock at approx. depths of 130-165 ft. Keller developed budget pricing for the caissons, but also suggested an alternative foundation concept that offered cost and schedule savings.
Keller proposed using overlapping jet grout columns to solidify the loose/soft upper soils and shed the building loads into the dense sands below. Tiedown anchors installed through the jet grout mass and socketed into the rock below resisted uplift loads.
Detailed engineering analysis necessitated the use of Plaxis 3D modeling software. Keller provided input with regard to the design and constructability of the solution. Extensive QA/QC was performed during construction to validate soilcrete properties.
The project team embraced the ground improvement solution based on cost and schedule savings, along with being able to execute this work on a small urban lot.