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Context Sensitive Rock Slope Design Solutions

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FHWA-CFL/TD-11-002
2011

Front Materials

• Cover
• Table of Contents
• Acronyms and Abbreviations

 

Technical Report Documentation Page

1. Report No. FHWA-CFL/TD-11-002	2. Government Accession No.			3. Recipient's Catalog No.
4. Title and Subtitle Context Sensitive Rock Slope Design Solutions				5. Report Date January 2011
				6. Performing Organization Code J2009-05
7. Author(s) Richard D. Andrew, Ryan Bartingale and Howard Hume				8. Performing Organization Report No.
9. Performing Organization Name and Address Yeh and Associates, Inc. 5700 E. Evans Ave. Denver, CO 80222				10. Work Unit No. (TRAIS)
				11. Contract or Grant No. DTFH68-07-D-00001
12. Sponsoring Agency Name and Address Federal Highway Administration Central Federal Lands Highway Division 12300 W. Dakota Ave., Suite 210B Lakewood, CO 80228				13. Type of Report and Period Covered Final Report June 2008 - December 2010
				14. Sponsoring Agency Code HFTS-16.4
15. Supplementary Notes COTR: Amit Armstrong, Ph. D., P.E. COTR: Khamis Haramy, FHWA-CFLHD. Advisory Panel Members: Khamis Haramy, Mathew DeMarco, and Roger Surdahl, FHWA-CFLHD; Khalid Mohamed, FHWA-EFLHD; Rich Barrows, FHWA-WFLHD; Scott Anderson and Barry Siel, FHWA-RC; Matt Greer, FHWA-CO; and Ty Ortiz, CDOT. This project was funded under the FHWA Federal Lands Highway Coordinated Technology Implementation Program (CTIP).
16. Abstract The Federal Highway Administration (FHWA) Federal Lands Highway Division (FLHD) evaluated the application of context sensitive solutions (CSS) for rock slope design. The application of context sensitive design in transportation is a method of developing facilities that fit within the engineered setting and preserve scenic, aesthetic, historic, and environmental resources while maintaining safety and mobility. Proper development of context sensitive solutions starts before the scoping stage and incorporates a number of factors, including community concerns, the effects of roadway development on the physical character of the surrounding area, and a visual prioritization of design considerations. Before starting construction, the contractor and land management agency should agree on a defined standard of performance and communication protocols to ensure that all project goals are attained. The aesthetics of common rock slope construction and mitigation practices can be enhanced with some modifications. Advantages, limitations, design guidelines, aesthetic value, construction materials, case examples, relative costs, and maintenance procedures are included for each method. Discussions are intended to guide the reader in CSS rock slope development.
17. Key Words CONTEXT SENSITIVE SOLUTION, CSS, ROCK SLOPES, ROCK EXCAVATION, AESTHETIC ROCK SLOPE, SLOPE STABILIZATION, ROCKFALL PROTECTION.			18. Distribution Statement No restriction. This document is available to the public from the sponsoring agency at the website https://flh.fhwa.dot.gov/.
19. Security Classif. (of this report) Unclassified		20. Security Classif. (of this page) Unclassified			21. No. of Pages 122	22. Price 0

Form DOT F 1700.7 (8-72)
Reproduction of completed page authorized

Table of Contents

• Acronyms and Abbreviations
• Introduction
• Context Sensitive Considerations For Rock Slopes
  • Understanding Context
  • The Design Process
    • Slope Stability Analysis
      • Geologic Features and Their Effects on Slope Character and Stability
    • Methods of Excavation
    • Safe and Natural-Looking Rock Cuts
    • Visual Prioritization
      • Short-Range Viewshed
      • Long-Range Viewshed
    • Stabilization, Protection, and Avoidance Measures
    • Building Consensus among Stakeholders
    • Preparing a Bid
• Blasting
  • Effect of Geologic Structure on Blasting Procedure
    • Discontinuity Sets
    • Slope Dip
    • Slope Strike
    • Mud and Soft Seams
  • Blasting Methods
    • Production Blasting
    • Controlled Blasting
  • Explosives
    • Dynamite
    • Ammonium Nitrate and Fuel Oil (ANFO)
    • Slurry (Water Gel)
    • Emulsion Explosives
  • Drilling Methods
    • Downhole Drilling
    • Step Drilling
    • Horizontal Drilling
  • Drilling Equipment
    • Downhole Drilling Rig
    • Track Drilling Rig (Percussion Drill Head)
    • Portable Crane-Mounted or Hand-Held Drills
  • Blasting Design
    • Presplit Blasting
    • Smooth Blasting
    • Cushion Blasting
    • Removing Drill Hole Traces and Blasting Scars
  • Ripping
    • Ripping Equipment
  • Breaking
• Rock Slope/landscape Integration
  • Physical Alterations
    • Major Slope Warping
    • Expanded Slope Rounding
    • Drainage Intercept Laybacks
    • Ditch Width Variation
    • Slope Angle Variation
  • Cosmetic Enhancements
    • Rock Staining
• Rock Slope Stabilization
  • Slope Geometry Alteration
    • Scaling
      • Hand Scaling
      • Mechanical Scaling
      • Trim Blasting
  • Reinforcement Systems
    • Internal Stabilization
      • Rock Anchors
      • Rock Mass Bonding
    • External Stabilization
      • Shotcrete
  • Drainage Systems
• Rockfall Protection
  • Rockfall Protection Design
    • Mesh and Cable Nets
      • Draped Mesh/Nets (Drapery Systems)
      • Anchored Mesh/Nets
    • Barriers
      • Earthen Barriers
      • Concrete Barriers
      • Structural Walls
      • Flexible Barriers
      • Attenuators
      • Barrier Design
    • Catchment Areas
      • Ditches
      • Hybrid Ditches
• Rockfall Mitigation Selection
  • Considerations
    • Security/Reliability
    • Constructability
    • Service Life
    • Suitability
    • Aesthetics
    • Cost Effectiveness
  • Comparison of Mitigation Methods
  • Maintenance Concerns
    • Managing Rockfall Incidents
      • Documentation
      • Action Plan
    • Maintenance Procedures
• Conclusions
• References
• Bibliography

List Of Symbols And Abbreviations

~

Approximately equal to

AASHTO

American Association of State Highway and Transportation Officials

ASTM

American Society for Testing and Materials/ASTM International

AWG

American Wire Gage

BS

British Standard

CALTRANS

California Department of Transportation

CDOT

Colorado Department of Transportation

CFLHD

Central Federal Lands Highway Division

CSS

Context Sensitive Solutions

DOT

Department of Transportation

EFLHD

Eastern Federal Lands Highway Division

FHWA

Federal Highway Administration

FLH

Federal Lands Highway

FLHD

Federal Lands Highway Division

FS

Factor of Safety

ft

Foot (feet)

ft2

Square foot (feet)

ft-tons

Foot-Tons

in

Inch(es)

kJ

KiloJoules

kPa

Kilopascal

m

Meter(s)

m2

Square meter(s)

MPa

Megapascal

MSE

Mechanically Stabilized Earth

PTI

Post-Tensioning Institute

PVC

Polyvinyl Chloride

U.S.

United States

WFLHD

Western Federal Lands Highway Division

List Figures

• Figure 1. Illustration. Rock discontinuity orientation parameters.
• Figure 2. Illustration. Details of typical slope cuts to be avoided.
• Figure 3. Illustration. Perspective view of the desired slope configuration and key design elements for different geographic settings. (a) Alpine environment with slope rounding and talus deposits (b) Arid/desert environment with blocky slope transitions and sparse vegetation.
• Figure 4. Illustration. Example of typical details for a sculpted rock cut.
• Figure 5. Illustration. Slope variation details used to enhance aesthetics.
• Figure 6. Illustration. The four primary mechanisms of slope failure.
• Figure 7. Illustration. Excessive end break caused by blasting parallel to jointing (modified from Konya and Walter 2003).
• Figure 8. Illustration. Excessive backbreak caused by blasting perpendicular to jointing (modified from Konya and Walter 2003).
• Figure 9. Illustration. The effect of joint orientation on the quality of the final wall face (modified from Matheson 1986).
• Figure 10. Illustration. Example of an excavation that blasts against the dip on the left side and with the dip on the right side (modified from Konya and Walter 2003).
• Figure 11. Illustration. Example of a blasting pattern that runs parallel to strike (modified from Konya and Walter 2003).
• Figure 12. Photo. Example of a presplit slope in massive sandstone. Note the abundant drill hole traces (half casts).
• Figure 13. Illustration. Cross section of a cushion blasting design using buffer holes to control the burden on the cushion holes (modified from Cummings 2002)
• Figure 14. Photo. Final configuration of a cushion-blasted slope in granitic rock.
• Figure 15. Illustration. Cross section of downhole and step drilling with sub-drilling techniques (modified from Cummings 2002).
• Figure 16. Illustration. Horizontal drilling design concept (modified from Cummings 2002).
• Figure 17. Photo. Drill hole traces left by horizontal drilling parallel to the rock face (fan drilling).
• Figure 18. Photo. Blast damage caused by horizontal drilling perpendicular to the rock face.
• Figure 19. Photo. Common track drill used to advance vertical blastholes.
• Figure 20. Illustration. Three options using lightly loaded, distributed charges in presplit blasting (modified from U.S. Department of the Interior 2001).
• Figure 21. Photo. Bulldozer with an integral ripping attachment.
• Figure 22. Photo. Typical hinge- or radial-style ripper (Nichols and Day 2005).
• Figure 23. Photo. Application of a hydraulic hammer attached to an excavator.
• Figure 24. Photo. A hydraulic hammer sculpting a rock face (the material to be removed has been outlined with common marking paint).
• Figure 25. Photo. A hydraulic hammer expanding a sculpted area, creating planting areas and more natural-looking slope variation.
• Figure 26. Photo. Completed rock slope prior to placement of topsoil and a native seed mix.
• Figure 27. Photo. Example of major slope warping on a cut slope.
• Figure 28. Photo. Slope rounding using long-reach excavator, Hyampom Road, California.
• Figure 29. Photo. Expanded slope rounding can prevent this type of erosion and overhang.
• Figure 30. Photo. Drainage intercept layback cut into a slope, Hyampom Road, California.
• Figure 31. Photo. Ditch width variation used to break up the slope face and mask drill hole traces.
• Figure 32. Photo. Ditch width variation can camouflage blast scars and drill traces.
• Figure 33. Photo. Slope angle variation helps match the natural topography of the surrounding area. The lower three tiers in the slope were excavated to simulate the natural benches in sedimentary units.
• Figure 34. Photo. Steep, exposed rock faces are good candidates for slope angle variations.
• Figure 35. Photo. Rock slope excavated using slope variation and sculpting techniques.
• Figure 36. Photo. Rock excavation shortly after construction. Note the stark contrast of the freshly excavated material and the naturally weathered rock surfaces. Glenwood Canyon, Colorado.
• Figure 37. Photo. Staining on the completed cut slope used to create a natural-looking rock face. Glenwood Canyon, Colorado.
• Figure 38. Photo. Application of stain to a newly constructed rock slope.
• Figure 39. Photo. Hand scalers removing loose material from a cut slope South Fork Smith River Road, California.
• Figure 40. Photo. Using a long-reach excavator for mechanical scaling.
• Figure 41. Illustration. Typical tensioned anchor (or rock bolt).
• Figure 42. Illustration. Typical untensioned rock dowel.
• Figure 43. Illustration. Example slope analysis diagram (modified from Hoek and Bray 1981).
• Figure 44. Photo. Tunnel crest supported with dowels that have been covered with colored grout.
• Figure 45. Photo. Rock bolts installed in an area where the surrounding rock has eroded away, reducing the effectiveness of the bolts.
• Figure 46. Photo. Installation of rock bolts using a track drill.
• Figure 47. Photo. Installing rock reinforcement using a drill rig suspended from a crane.
• Figure 48. Photo. Installation of polyurethane resin from man lift, Poudre Canyon, Colorado
• Figure 49. Photo. Polyurethane resin used in a fracture, Poudre Canyon, Colorado.
• Figure 50. Photo. Welded wire mesh can be attached to the rock face before shotcrete is applied.
• Figure 51. Photo. Shotcrete can be used to protect a slope from erosion-and sculpted to mimic the natural rock face (Ada County Highway District 2003).
• Figure 52. Photo. Sculpted shotcrete used to stabilize a tunnel portal (the area directly below the dry-stack wall is the sculpted shotcrete).
• Figure 53. Photo. Application of the first layer of structural shotcrete.
• Figure 54. Photo. Installation of the first layer of structural shotcrete.
• Figure 55. Photo. Application of the final sculpted shotcrete façade.
• Figure 56. Photo. Completed structural shotcrete support, ready for staining.
• Figure 57. Illustration. Effective rockfall protection design requires an accurate slope profile, which identifies source areas, launch points, and runout zones (Brawner 1994).
• Figure 58. Photo. A rockfall-prone slope draped with unsecured wire mesh. Wolf Creek Pass, Colorado.
• Figure 59. Photo. Erosion can lead to failure in a drapery system if the mesh is not secured sufficiently beyond the area of slope degradation at the top of the slope.
• Figure 60. Photo. Rock slope treated with colored draped rockfall mesh.
• Figure 61. Photo. A drapery system that was not visually mitigated.
• Figure 62. Photo. An anchored Tecco mesh system secured by a grid of rock bolts, US 299 in Northern California.
• Figure 63. Photo. A detail of the anchors used to secure the mesh system shown above.
• Figure 64. Photo. Installation of a flexible rockfall barrier on Guanella Pass, Colorado.
• Figure 65. Photo. A conventional earthen berm can protect a highway from rockfall with low bounce height and low rotational energy.
• Figure 67. Photo. Concrete barriers used as a rockfall protection measure. Notice the damage caused by a large rock impact.
• Figure 68. Photo. Example of a ring-net flexible barrier.
• Figure 69. Illustration. Design of a typical rockfall fence (modified from Transportation Research Board 1996).
• Figure 70. Photo. An attenuator combines a standard fence with a draping system. Georgetown, Colorado.
• Figure 71. Illustration. Cross-section of a typical Oregon ditch design (modified from Pierson, Gullixson, and Chassie 2002).
• Figure 72. Photo. A hybrid ditch design.

List of Tables

• Table 1. Description, advantages, and limitations of common excavation practices.
• Table 2. Explosives commonly used in transportation projects.
• Table 3. Comparison of vertical drilling rigs (modified from Konya and Walter 2003).
• Table 4. Parameters for drilling in a presplit blasting operation (modified from U.S. Department of the Interior 2001).
• Table 5. Parameters for drilling in a smooth blasting operation (modified from U.S. Department of the Interior 2001).
• Table 6. Parameters for drilling in a cushion blasting operation (modified from U.S. Department of the Interior 2001).
• Table 7. Overview of rock slope/landscape integration techniques.
• Table 8. Overview of stabilization procedures and their limitations.
• Table 9. Properties of different rock-bonding products (Arndt, DeMarco, and Andrew 2008).
• Table 10. An overview of rockfall protection measures and their limitations.
• Table 11. Recommended mesh material usage as a function of block size and slope angle (modified from Muhunthan et al. 2005).
• Table 12. Properties of different rockfall and slope stability mitigation measures.
• Table 13. Maintenance procedures for mitigation measures.

Acknowledgments

We are grateful for the contributions and cooperation of the Central Federal Lands Highway Division (CFLHD) advisory panel (Khamis Haramy, Mathew DeMarco, Roger Surdahl, Khalid Mohamed, Rich Barrows, Scott Anderson, Barry Siel, Matt Greer, and Ty Ortiz). Specifically, Khamis Haramy's efforts and contributions in the role of CFLHD's Contracting Officer's Technical Representative (COTR) are greatly appreciated. Finally, we extend our thanks to Martha Connors who performed the detailed editing of this document.

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