"Interaction between Geotechnical and Structural Engineer during Complex Underpinning Design & Construction in Urban New York

Douglas Roy, P.E., Minfei Yang, EIT (GZA New York City)

This paper discusses the interaction between geotechnical and structural engineer during complex underpinning design and construction of an existing three-story building (a former funeral home, and parking garage in later years) located on Ludlow Street in the Lower East Side area of Manhattan, New York. The existing 1930-built Neo-Gothic building with a steel frame and concrete block structure has an approximate footprint of 4,375 square feet and a partial 10-foot-deep cellar. Major alterations for this manufacturing-type building that will be home of a private members-only club for those in film, media, and creative industries, will include expansion of the partial cellar to a full cellar requiring excavation of up to 14 feet below the ground floor slab, addition of a new elevator shaft, and other interior renovation. The site is bounded to the west by one one-story building supported on concrete footing and a backyard, to the south by a four-story building with one basement level supported on rubble footing, to the north by a six-story building with one basement level supported on rubble footing and to the east by Ludlow street.

This paper will describe some of the challenges and solutions during the underpinning design and construction of the project and adjacent buildings, including interaction with the Structural Engineer to evaluate underpinning of existing heavily loaded columns (up to 270 kips) and intermediate support during construction; coordinated load transfer and mat slab analyses using SAFE and traditional shallow foundation settlement calculations to study the anticipated building settlement; construction observation during underpinning that revealed wider and deeper foundations beneath the columns; use of a liner wall between existing concrete footings for load-transfer; utilizing raker and heel block system in lieu of traditional soil tieback anchors to avoid intrusion into adjacent building yard. Real time settlement data of the existing and adjacent buildings was collected during underpinning utilizing automated total station (AMTS) and tilt meters. This paper will include settlement data illustrating the increase of measured settlement versus the progress of underpinning, as well as the comparison between the estimated settlement of building and real time settlement data during underpinning.

Learning points:

  • What is the procedure of concrete underpinning and considerations for adjacent buildings?
  • What lateral support system was used during underpinning?
  • Importance of interaction between geotechnical and structural engineers to design underpinning and permanent foundation element.
  • What are the challenges and solutions to underpin heavy loaded columns?
  • Protecting the existing and adjacent buildings by implementing a building monitoring system
  • Guidance on predicting anticipated building settlement during underpinning.