In 2015, Rockefeller University, a historic, cloistered medical research campus on the Upper East
Side of Manhattan along the East River, embarked on the construction of a new building. The
building would be squeezed into a tight slot between adjacent buildings and over the top of the
busy six‐ lane FDR Drive. The foundations on either side of the FDR Drive presented different
challenges to the design and construction of mini‐ caisson piles.
On the upland side west of the FDR Drive, drilling contractor Posillico offered the owner a
value‐ engineered alternate to replace a proposed deep pier/wall on rock and rock anchors with a
pile cap supported by 16 battered mini‐ caissons. An unconventional pile design featuring a steel
pipe installed within the drill casing allowed the piles to develop the required lateral stiffness
and isolate load transfer below the adjacent existing building foundation. The alternate solution
eliminated the rock anchors and reduced the costly rock excavation by almost 2, 700 tonnes (3000
tons) from the original plan. The owner also requested that the contractor accelerate the schedule
in order to allow for steel erection to begin 2 months earlier than planned. On the riverside east
of the FDR Drive, Posillico redesigned the 340‐ mm (13‐ 3/8‐ inch) diameter 5, 425‐ kN (600‐ ton)
mini‐ caissons to 457‐ mm (18‐ inch) diameter for 10, 850‐ kN (1200‐ tons). This led to a reduction in
pile quantity and accelerated an important schedule milestone. The lateral requirements for both
foundations required drilling the casing through the bedrock and partially extracting it to achieve
the load transfer through friction in the rock socket.
This paper reviews the unconventional pile design details. It also explains how a proprietary
under‐ reaming drilling system allowed the contractor to meet the compressive and lateral design
requirements while also allowing for the use of smaller rigs than would otherwise be needed.
Additionally, the paper reviews some of the difficult urban construction conditions within limited
access environments including overhead and underground utilities, heavily quipment logistics and
tight coordination of protection of traffic on the
mely busy FDR Drive.
Subjects: Rockefeller University, mini-caissons, Posillico
Author: Andrew Burns, PE, Michael Quasarano, PE
Publisher: ISM, DFI, ADSC