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The National Academies

NCHRP Synthesis 20-05/Topic 54-15 [New]

Prevention and Mitigation of Surficial Slope Failures on Highway Embankment Slopes
[ NCHRP 20-05 (Synthesis of Information Related to Highway Practices) ]

  Project Data
Funds: $55,000
Authorization to Begin Work: 4/29/2023 -- estimated
Staff Responsibility: Leslie C. Harwood
Fiscal Year: 2023

Preliminary Scope

Highway embankment slopes with cohesive materials 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 softens over the time and loose 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, 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 concern, 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 current practices on training for, design, identification, prevention, and mitigation of surficial slope failures.

Information to be gathered includes (but is not limited to):
• Design of new embankment slopes, specifically related to surficial stability;
• Use of embankment slope materials;
• Maintenance costs to repair surficial slope issues;
• Proactive methods used to address surficial instability;
• Mitigation techniques for addressing surficial slope instability; and
• Impact of regional climate focusing on rainfall and temperature.

Information will be gathered through a literature review, a survey of state DOTs, and follow-up interviews with selected agencies for the development of case examples. Information gaps and suggestions for research to address those gaps will be identified.

Information Sources (Partial):
• Stauffer P.A., and Wright, S.G. (1984). An Examination of Earth Slope Failures in Texas. Report Number 353-3F, Center for Transportation Research, The University of Texas at Austin, Texas.
• Pradel, D., and Raad, G. (1993). “Effect of Permeability on Surficial Stability of Homogeneous Slopes”. Journal of Geotechnical Engineering, ASCE, 119 (2).
• Day, R.W. (1994). “Surficial Stability of Compacted Clay: Case Study”. Journal of Geotechnical Engineering, ASCE, 120 (11).
• County of Los Angeles Department of Public Works. Manual of Preparation of Geotechnical Reports. 2013. Geotechnical and Materials Engineering Division.

TRB Staff
Leslie Harwood
Phone: 202-334-2312
Email: lharwood@nas.edu

Meeting Dates
First Panel: TBD
Teleconference with Consultant: TBD
Second Panel: TBD

Topic Panel
TBD

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