Slope Rehabilitation at the Baltimore-Washington Parkway with Rammed Aggregate Piers

The Baltimore-Washington Parkway is a major traffic artery traveled by daily commuters in suburban Washington, D.C. Much of the parkway roadbed lies on a raised embankment constructed to allow for grade separation between the parkway and surface streets, facilitating access to the parkway. After a series of rainstorms in the fall of 2002, the fill embankment at the recently reconstructed Route 197 interchange failed, with resulting settlement and lateral movement of a retaining wall that supported the southbound lanes of the parkway. The slide encroached on the traffic lanes and jeopardized the integrity and safety of the parkway. After analyzing a variety of possible solutions, FHWA and the National Park Service opted to stabilize the slide by using Geopier rammed aggregate piers, acting in concert with a toe berm stabilized with Tensar highstrength structural geogrid. The rammed aggregate piers improved the stability of the slope by providing significant increases in the composite shear resistance because of their high angle of internal friction (44° to 52°). A case history is presented of the use of rammed aggregate piers to stabilize a landslide. The analytical methods used in the design solution are presented along with a description of the construction sequence. This study is significant because it describes how a simple and cost-effective solution may be implemented to stabilize landslides.