DESCRIPTION

Howard University is revitalizing 4th Street with the construction of two state-of-the-art 6 and 7-story residence halls. Both buildings will provide approximately 1,360 beds in 700 units, including two-person semi-suites for students and independent apartment units for faculty and staff.

Pursuing LEED Silver Certification

CHALLENGE

College Street- soils below the mat foundation of the College Street residences generally consist of loose to very dense SAND underlain by soft to very stiff CLAY.

Bryant Street- Soil conditions generally consist of 5 to 23 ft of FILL underlain by very soft to stiff CLAY and clayey SILT and medium to very dense GRAVEL and sandy GRAVEL.

SOLUTION

In general, the loose and soft soil conditions combined with the heavy column loads associated with the 6 and 7 story buildings required a stiffer element than just an aggregate pier, so a Geopier rigid inclusion consisting of Geopier grouted Impact RAP elements were used.

At the College Street site soil conditions were generally considered suitable for support of the proposed building, however, due to existing large diameter drilled shafts which were supporting a portion of the buildings footprint Grouted Impact Piers were needed to control differential settlement. 262 Grouted Impact pier elements were installed ranging in depth from 20 to 26 ft to limit differential settlement between the drilled shaft and grouted impact supported columns.

For Bryant Street, soil conditions were found unsuitable for conventional spread footings even when supported by aggregate piers. This was primarily due to large amounts of fill and soft silts in the upper strata which could potentially lead to excessive settlement under the proposed building loads (column loading up to 750 kips, and mat foundation loads from 580-1825 kips).

727 Grouted Impact Pier elements were selected to span the soft soil zones and were founded in the denser sands and gravels at depths of 20 to 40 ft.

A load transfer pad consisting of 1 one foot thick granular pad and a 2 foot thick ungrouted Impact Pier element was used to spread out the stress from the Geopier rigid inclusion on to the bottom of the slab.