Scaling loose rocks from slopes adjacent to highways is an effective measure for reducing the risk of rock fall. Removal is typically done by hand using pry bars or with mechanical assistance such as jacks, hydraulic splitters, air bags, or heavy machinery. In some cases, trim blasting techniques are considered as part of a scaling program. Slope access is generally accomplished by personnel on foot and by rope access; however, telescopic boom-lifts and crane baskets are also used.
Scaling is typically done after sudden or prolonged rock fall activity. However, with the aging of the nation’s highway system, there is an increasing need to address long-term weathering of constructed and natural slopes along highway corridors. The required frequency of scaling depends on the slope characteristics, geology, rock structure, local climate, performance expectations, consequences of rock fall impacts, and budget availability. Some departments of transportation (DOTs) have developed programs for scaling that are performed at regular intervals on a proactive basis.
The objective of this synthesis is to document current practices for rock slope scaling next to highways. The scope includes documenting methods used by DOTs for specifying, estimating, and contracting scaling and debris removal, and assessing scaling performance.
Information to be gathered includes (but is not limited to):
• Methods for estimating the quantity and type of scaling required for a project;
• Methods for estimating scaling production rates (e.g., project duration);
• Scaling contract plans for contractor bidding;
• Scaling specifications (e.g., contractor qualification requirements, methods used for measurement and payment, incidental items);
• How DOTs administer scaling (e.g., on-call, design-bid-build, emergency);
• Approaches to temporary roadway protection and traffic control while scaling;
• Methods for determining project completion; and
• Documented methods for assessing performance of scaled slopes.
Information will be gathered through literature review, a survey of DOTs, collection and analysis of relevant documents, and interviews with selected agencies for the development of case examples. Knowledge gaps and suggestions for research to address those gaps will be identified.
Information Sources (partial):
• Andrew, Richard D., Bartingale, Ryan and Hume, Howard Context Sensitive Rock Slope
Design Solutions. Federal Highway Administration, Central Federal Lands Highway
Division: Report No. FHWA-CFL/TD-11-002, January 2011.
• Brawner, C.O. 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, March 1994.
• Turner, Keith A., and Schuster, Robert L. Rockfall Characterization and Control.
Transportation Research Board of the National Academies, Washington D.C., 2012.
• Wyllie, Duncan C. and Mah, Christopher W. 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, October 1998.
• Wylie, Duncan C. and Mah, Christopher W. Rock Slope Engineering. Civil and Mining, 4th
Edition. Spon Press, New York. 2004.
• TRB workshop on rock slope scaling (2018 TRB annual meeting) and subsequent e-circular
Jo Allen Gause
First Panel: October 18, 2018, Washington, DC
Teleconference with Consultant: November 5, 2018, 2:00 p.m., EST
Second Panel: July 16, 2019
Jody Kuhne, North Carolina DOT
Nicole Oester, Colorado DOT
Krystle Pelham, New Hampshire DOT
Daniel Pradel, The Ohio State University
Todd Reccord, Ameritech
Stephen Taliaferro, Ohio DOT
Thomas Whitman, California DOT
Khalid Mohamed, Federal Highway Administration
Nancy M. Whiting, Transportation Research Board