O Street Retaining Wall
- Location: Washington, DC
- Owner: District of Columbia Department of Public Works
- Technique(s) Utilized: Anchors, Post-Tensioned Anchor Walls
Background
Movements were noted along a 130-foot section of an anchored retaining wall on O Street in Washington, D.C. A geotechnical assessment of the wall concluded that the wall failure was due to improper drainage behind the wall, the presence of zones of highly plastic slickensided clay, and the lack of corrosion protection on threadbars used as tieback supports. In July of 2000, the owner invited contractors to propose a design-build solution to rehabilitate the wall. Nicholson proposed stabilizing the existing wall and building an anchored soldier pile and precast lagging wall in front of it. A new and improved drainage system would also increase the amount of water directed toward the storm sewer running along O Street.
To stabilize the existing wall, several steps were taken before construction of the new wall. These included: demolition of a distressed residential garage building; removal of about 100 feet of the wall; and installation of 9 weep holes in each wall panel to promote drainage of any permeable layers overlying clay layers. A test anchor program was undertaken to determine the best anchor installation method as well as their load capacity and load properties. In order to prevent further toe movement of the existing wall, shafts were drilled on skipped spaces and refilled on later work shifts.
Construction of the new anchored soldier pile and precast lagging wall began by using a rubber tire mounted drill rig with a 36-inch auger attached to a Kelly bar to drill holes for the soldier pile beams. A total of 135 beams were installed using a tracked hydraulic crane. Structural concrete with a compressive strength of 3,500 psi was placed in each caisson to secure the soldier pile. To promote drainage between the new and original wall, a 4-foot wide gravel-filled geodrain was built. Precast concrete walers and lagging panels were installed in their respective bays. A total of 262 tieback anchors were installed in the new wall.
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