Potomac Center North
- Location: Washington, DC
- Owner: The JBG Companies
- General Contractor: James G. Davis Construction
- Technique(s) Utilized: Micropiles
Background
Potomac Center North is a 1 million-square-foot office building overlooking the Potomac River in Washington, DC. An addition of three new floors was to be added to the structure. The existing building column spread footings were not able to support the additional loads.
To support the new loads, micropiles were specified. The contract called for the installation of 188 micropiles; 156 through the existing spread footings in the building’s
underground garage and 32 installed outside of the existing building at new column locations. With only 7 feet of headroom, the garage offered limited access for the interior micropile operations. The exterior piles had to be installed through obstructions from abandoned building foundations.
Nicholson was awarded the micropile contract which
required the design of the micropile details. For this project, Nicholson used TITAN micropiles, which are continuously threaded, self drilling, hollow thread bars that are installed by rotary drilling using a grout flush to stabilize the drill hole.
For the interior micropiles, a special drill mast was fabricated for drilling in the low headroom. The interior piles were installed through a core hole that was grooved to provide a connection to the existing footing. While drilling the exterior piles, crews faced another challenge when they encountered obstructions from abandoned building foundations. The crew predrilled the obstructions with a down hole hammer.
The micropiles had design loads that ranged from 10 to 90 tons with pile diameters that varied from 5 to 10 inches. Overall, Nicholson installed 188 micropiles with lengths that ranged from 20 to 35 feet. Nicholson conducted two pile load tests, one compression and one tension.
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