Court House Metro Plaza
Courthouse Metro Plaza is a mixed used, 3-story, 53,000 sf brick and precast concrete structure with an operating underground metro station located just below the surface of the site.
WMATA (Washington Metropolitan Area Transit Authority) regulates all buildings constructed near their underground tunnels; limiting the top of tunnel stress (300 psf) for new construction. With tunnels located both below the new construction as well as a pedestrian tunnel set 5 ft off the proposed footings, controlling both horizontal and vertical stress was paramount to the success of this project.
Soils generally consist of fill, sampled as clays with variable amounts of sand and gravel from depths of 7 to 17 ft with N-values ranging from 4 to 66 bpf; underlain by Sands and Gravels with N-values ranging from 9 to 50 blows per 4”inch increment. Groundwater was encountered at depths ranging from 38 to 43 ft below the ground surface.
A mixed pier, part Geopier and part concrete, was used adjacent to the pedestrian tunnel to control horizontal stress. The concrete pier was used to both span the pedestrian tunnel, without applying significant stress, and to transfer the spread footing load into a Geopier below. The concrete pier could then shed the load through shaft friction and not end bearing, preventing large stress increases on the tunnels below.
Loading for the mixed use project includes spread footing loads from 30 to 575 kips, with load combinations as high as 1,210 kips, and wall loads range from 5 to 11.5 kips/ft. A grade beam system was used to transfer loads to footings for frame loading directly above the existing station structure. 128, 30-inch Geopier elements were installed from 8 to 9 ft, with rigid inclusion segments from 4 to 6 ft.
The Jenco Group
Dietze Construction Group
Bignell Watkins Hasser Architects
The Watkins Partnership
ECS Mid-Atlantic, LLC
Metrorail Structure & Tunnel Monitoring