Synthesis of Information Related to Highway Practices. Topic 54-15. Prevention and Mitigation of Surficial Slope Failures on Highway Embankment Slopes

Highway embankments, specifically referring to 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 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. In addition, cohesive materials near slope surface can soften over time and lose strength. The soils along the slope face can swell and develop seepage parallel to the slope. This can result in surficial slope instability. Surficial slope instability is also dependent on regional climate and vegetation which can change over time. Surficial slope stability issues in highway embankment slopes have been reported and typically occur during heavy rains. Only some state and local agencies have incorporated requirements to evaluate surficial slope stability in their design guidelines. It is important to incorporate surficial slope stability analysis which includes a saturated depth which is appropriate for the specific site conditions. Site conditions that can impact stability include geometry (e.g., steepened slope), fill materials, and climate. When the analyses show a potential for instability, slope stabilization techniques such as mechanical, chemical, and biological stabilization methods may be required to address the surficial slope instability. Surficial slope failures can create safety concerns, traffic congestion, and increased maintenance. A proactive approach for the mitigation of surficial slope instability is generally not considered in the design. A reactive approach to fix the failed slopes as a maintenance activity is more common and significant resources are required to fix surficial slope failures. 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.


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Filing Info

  • Accession Number: 01845591
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 20-05, Topic 54-15
  • Files: TRB, RIP
  • Created Date: May 18 2022 10:58AM