College Ave Office Building & Garage

The New Haven Downtown Crossing is a multi-phase redevelopment project.  The first phase featured the construction of a 14-story office building and parking garage located on College Street.

The project team was faced with a variety of geotechnical challenges including the presence of fill, soft organic soils, compressible natural sand/silt and a relatively high groundwater table. Supporting footings and slabs directly on the existing unimproved soils would have led to excessive settlement.

Geopier Rammed Aggregate Pier® (RAP) and GeoConcrete® Columns (GCCs) allowed for traditional shallow footings and slab-on-grade construction.  The GGCs were designed to limit the total and differential post-construction footing settlement to less than 1 ½ inches and 1 inch respectively within the GCC-improved zone, and provided a maximum allowable footing bearing pressure of 9.5 kips per square foot. They were installed using a displacement technique that did not require dewatering and did not generate excess spoils, ultimately reducing premium dewatering and off-site soil disposal costs. 

More than 900 GeoConcrete Columns and 100 Rammed Aggregate Piers were installed. The Geopier designer engineered a structural footing pad beneath the footings to help transfer footing stresses to the GCCs and surrounding matrix soil. The footing pads also provided a stable sub-grade for footing construction. 

A full-scale modulus test was conducted on a test footing supported by a group of three GCCs to 150% of the GCC element design stress. Two individual GCC modulus tests were also performed to 150% of the GCC element design stress.