Design manuals for rock slope and rockfall mitigation have been in use by departments of transportation (DOTs) since the 1960s. Software tools have made complex data analyses faster and easier than in decades past. These manuals and software tools have proved invaluable to practitioners, helping them design and evaluate rock slopes adjacent to highways and the management of rockfall hazards.
While there are no national standard goals and objectives for rock slope design and rockfall management, some DOTs have formally or informally adopted their own design goals and objectives. Examples of design goals DOTs have adopted, either on a project-specific or statewide basis, include:
• Acceptable percentages of rockfall debris that may reach the travel lanes
• Improvement of the percentage of rockfall debris being caught in the roadside ditches
• General reductions in maintenance efforts or safety concerns
• Reductions in hazard “scoring,” using evaluation systems such as the Rockfall Hazard Rating System
The objective of this synthesis is to document DOT practices for the design of rock slopes and rockfall management.
Information to be gathered includes (but is not limited to):
• Percentage of new and rehabilitated rock slopes within DOTs;
• Agency versus consultant or contractor design (approximate percentages);
• Documented design goals and objectives;
• Consideration of project delivery, constructability, maintenance, asset management, aesthetics, life cycle costs, resilience initiatives, highway system designation, or risk management plans in the design process;
• Technical factors that guide design (e.g., deterministic or probabilistic slope stability models, rock mass characteristics, roadside ditch containment percentages, rockfall frequency, new versus rehabilitated rock slopes, performance-based standards);
• Risk considerations for rock slope design and management (e.g., consequences of slope failure, rock fall, impact on the travelling public, risk sharing, monitoring);
• Design practice for mitigation measures (e.g., rockfall barriers, rock bolts and dowels, draped mesh, rockfall attenuators, pinned mesh systems); and
• Performance measures for rock slope and rockfall mitigation (e.g., percentage of rockfall retained in ditches, number of repeat failure incidences)
Information will be collected through literature review, a survey of 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):
• Wyatt, T.R. (2020). Potential Liability Associated with Unstable Slope Management Programs. NCHRP Legal Research Digest 82. Transportation Research Board of the National Academies, Washington D.C.
• Andrew, R. D., Bartingale, R., and Hume, H. (January 2011). Context Sensitive Rock Slope Design Solutions. Federal Highway Administration, Central Federal Lands Highway Division. Report No. FHWA-CFL/TD-11-002.
• Brawner, C. O. (March 1994). Manual of Practice on Rockfall Hazard Mitigation Methods. Federal Highway Administration, National Highway Institute. Training Course No. 13219, Participant Workbook, Publication No. FHWA SA -93-085.
• Turner, K. A., and Schuster, R. L. (2012). Rockfall Characterization and Control. Transportation Research Board of the National Academies, Washington D.C.
• Wyllie, D. C., and Mah, C. W. (October 1998). Rock Slopes Reference Manual. Federal Highway Administration, National Highway Institute. Training Course in Geotechnical and Foundation Engineering, NHI Course No. 13235 - Module 5. Publication No. FHWA HI-99-007.
• Wyllie, D. C., and Mah, C. W. (2004). Rock Slope Engineering. Civil and Mining, 4th Edition. Spon Press, New York.
• Wyllie, D. C. (2018). Rock Slope Engineering. Civil Applications, 5th Edition, CRC Press, New York.
Jo Allen Gause
First Panel: October 16, 2020, Washington, DC
Teleconference with Consultant: November 26, 2020, 2:00 p.m., Eastern
Second Panel: June 29, 2021
Robert Group, Colorado Department of Transportation
Joe Hudak, Minnesota Department of Transportation
Jody Kuhne, North Carolina Department of Transportation
Kate Maguire, Maine Department of Transportation
Anil Patnaik, University of Akron
Krystle Pelham, New Hampshire Department of Transportation
Jennifer Nicks, Federal Highway Administration
Robert Shea, Transportation Research Board