SGH evaluated Building 3’s condition and concluded it was safe for occupancy without shoring. We recommended additional movement and vibration monitoring throughout the investigation and remedial work.
We performed a subsurface investigation, including soil test borings, test pits, groundwater observation wells, and laboratory soil testing. SGH determined Building 3’s movement was caused by basal heave of the soft Connecticut Valley Varved Clay (CVVC) stratum underlying the site and soil nail wall used as the excavation support system adjacent to Building 3. To minimize the potential for additional movement, we proposed construction sequencing modifications. SGH designed alternate foundations and an excavation support system allowing the contractor to safely continue construction of the new tower. Our design included the following:
Installing jacked piles to underpin Building 3’s adjacent exterior brick masonry bearing wall
Replacing certain driven, steel H-piles specified for the tower with drilled-in micropiles to minimize CVVC stratum disturbance due to H-pile installation
Installing an internally-braced, soldier-pile and lagging wall to replace the soil nail wall
Installing geotechnical instrumentation, including crack gauges, vertical extensometers, and inclinometers to monitor Building 3 and ground movements during construction
By implementing our proposed modifications, the contractor completed the North Tower in a timely manner and without additional damage to Building 3.