Harlem Hospital Center – Major Modernization
Harlem, New York City, NY
Platinum Award for Engineering Excellence from the American Council of Engineering Companies (ACEC) of New York
Modernization of a more than 100-year old teaching hospital’s campus included construction of a new six-story, 150,000 square foot pavilion to connect to two existing buildings in New York City. A geotechnical evaluation performed for the project concluded that the project site’s subsurface conditions were prone to liquefaction under the NYC Building Code stipulated seismic event and that the structure and its ground floor needed to be supported by deep foundations. Drilled shafts were recommended for use and they were required to be socketed 20 feet into bedrock, the depth to which ranged from 85 to 130 feet below the site grades.
A peer review of the geotechnical report acknowledged the site soils were prone to liquefaction but identified that the installation of drilled shafts would be both difficult and time consuming. The site was formerly the location of several buildings of which the foundations, floor slabs and walls of the former structures were present below grade and infilled with miscellaneous building demolition debris. The need to maintain utility services to adjacent active hospital facilities made pre-excavation of obstructions for the installation of drilled shafts problematic.
The peer review resulted in recommending that the new building be supported on conventional spread foundations bearing over ground densified through compaction grouting. The work was performed within four feet of adjacent buildings and immediately adjacent to a utility and pedestrian tunnel and several underground utilities, all of which had to remain in service during the work’s performance. Further complicating the work was the presence of a nearby trailer-mounted MRI facility which had to remain operational throughout the grouting program and therefore imposed very strict vibration limitations during the work’s performance.
Specifications for the compaction grouting required each compaction grouting rig to be equipped with gauges and other instrumentation, including a continuous data logging system to control, measure and record grout injection pressures as well as the rate and volume of each stage of grout injection. Manometers, tell-tales, lasers, inclinometers and seismographs were utilized to monitor vertical and lateral displacements of existing structures and vibrations transmitted to the same during the compaction grouting program. In addition, continuous “real-time” measurements were made using a sophisticated monitoring system and software (ShapeAccelArray) that allowed data to be collected automatically.
Real-time monitoring of lateral ground deflections at depth using the ShapeAccelArray instrumentation resulted in the need to lower the planned grout injection pressures to ensure lateral ground deflections adjacent to the pile supported building were maintained lower than one-quarter of an inch. This same instrumentation proved invaluable in determining that the vibration levels transmitted to the operating MRI facility were acceptable. Rigs equipped with gauges and other instrumentation provided operators with the ability to closely monitor and control the grouting process. Heave of existing utilities, spread foundations and the ground floor of one adjacent building were thereby prevented from occurring.
To share the success of this project with the engineering profession, a technical paper was published and presentations given to ASCE Chapter Groups.