<p><p><h2>Project Summary/Scope:</h2>After a long period of heavy rains, the approximately 2H:1V slope began to show signs of distress. The failure led to horizontal and vertical movements of a safety barrier wall and threatened a wooded area at the toe of the slope. The slope failure extended approximately 330 feet.</p><p><strong>Subsurface conditions:</strong> Highly plastic Coastal Plain soils with SPT N-values between 5 and 53 blows per foot.</p><p>Based on the slope geometry, subsurface conditions, observed surface conditions, and inclinometer data, the cause of the failure appeared to be softening of the plastic clay embankment soils. Stability calculations were performed on the existing slope geometry using the existing failure surface determined by the observed pavement cracking. Based on results of the back-analysis, a drained internal friction angle of 18 degrees and a cohesion of 20 psf were used in design. Slope stabilization options included retaining walls, a rock buttress system, and excavation and replacement of a portion of the slope soil. A toe berm and foundation reinforcement with rammed aggregate piers was found to be the most economic solution. The upper and lower portions of the slope were cut to approximately 2H:1V and 4H:1V, respectively. The lower portions of the slope are armored with rip-rap. A total of 472 rammed aggregate piers were installed in 30-inch holes under the lower portion of the slope. Pier depths ranged between 10 and 21 feet.<br><h2>Complementary Technologies Used:</h2>Geosynthetic reinforced embankment berm<br><h2>Alternate Technologies:</h2>Excavation and replacement, retaining wall structures, and rock buttress were considered.<br><h2>Case History Author/Submitter:</h2>Scott Saunders, P.E.<br>Federal Highway Administration Scott.Saunders@fhwa.dot.gov<br><h2>Project Technical Paper:</h2>O’Malley, E. S., Saunders, S.A., and Ecker, J.J. (2004). “Slope rehabilitations at the Baltimore-Washington Parkway with rammed aggregate piers.” Transportation Research Record: Journal of the Transportation Research Board, 1974, 136-146.<br><h2>Data Case History Prepared:</h2>November, 2012</p></p>