Slope Failure & Landslide Triggered by an Intense Rainfall Event-Forensic Investigations and Remedial Design

In May 2014, sustained rainfall triggered a landslide in Fort Washington, MD leading to significant ground movements, slope failures, and pavement distresses along a 427-m section of Piscataway Drive. The damaged roadway, fractured water and sewer pipes, power lines and uprooted trees on a 19-m hillside slope led to immediate road closure and emergency evacuation of 28 homes. The site is within an area containing sensitive Marlboro Clays and characterized by steep slopes and historic landslides. This paper discusses the geotechnical forensic investigations conducted to determine the cause of the landslide, monitor post-failure movements, and develop remedial design for stabilizing the slopes. The project challenges included right-of-way constraints, legal issues related to site and building safety, utility relocations, regulatory reviews, and environmental requirements. The selected cost-effective ground improvement and site stabilization consisted of rows of driven steel H-piles to depths up to 21 m along the roadway; and geogrid reinforced hillside slopes.