Highway embankments, where earthen material is placed and compacted to raise the grade of a highway above the level of the existing surrounding ground surface, may be constructed with cohesive materials that can become dried and desiccated causing shrinkage of the soil during the summer. This can result in cracks and fissures near the surface of the slope. During heavy rains, water infiltrates into the cracks and fissures, saturating the slope surface materials, and creating a perched water table. The increased water pressure has the effect of reducing the effective shear strength of the soil while simultaneously increasing the driving forces.

Only some state and local agencies have incorporated requirements to evaluate surficial slope stability in their design guidelines. It is important that such guidelines incorporate surficial slope stability analysis, including a saturated depth appropriate for the specific site conditions. When an analysis shows the potential for instability, slope stabilization techniques such as mechanical, chemical, and biological stabilization methods may be required to address the surficial slope instability. 

The objective of this synthesis is to document state DOT practice on identification, investigation, design guidance and requirements, prevention, and mitigation of surficial slope failures. 

Information for this study was gathered through a literature review, a survey of state DOTs, and follow-up interviews with selected DOTs. Case examples of four state DOTs provide additional information on practices for identification, investigation, design guidance and requirements, prevention, and mitigation of surficial slope failures. 

Darren Beckstrand of Landslide Technologies, Portland, Oregon, collected and synthesized the information and wrote the report, supported by Aine Mines and Michael Bunn of Landslide Technologies. The members of the topic panel are acknowledged on page iv of this report. This synthesis is an immediately useful document that records engineering considerations and practices that were acceptable within the limitations of the knowledge available at the time of its preparation. As progress in research and practice continues, new knowledge will be added to that now at hand.

The completed report can be found at NCHRP Synthesis Report 617.