Design Practices for Rock Slopes and Rockfall Management (2022)

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60 Survey Responses A P P E N D I X B Part C: Rock Slope and Rockfall “Demographics” Q1: How many road miles is your agency responsible for? (Self-Reported) 15,000 4,843 0 80,000 16,395 8,033 49,546 6,859 2,500 36,000 2,000 60,000 0 6,137 395,000 10,000 58,000 3,719 500 50,000 12,000 38,770 8,900 1,000 7,500 12,923 12,000 43,000 9,617 9,000 11,696 23,400 Q2: How many rock slopes is your agency responsible for? If an inventory is not available, an approximate count based on experience (±100) is okay. 381 200 0 750 2,600 2,000 100 5,900 200 75 3,666 4,060 1,500 410 300 50 10,000 5,270 0 500 500 100 4,000 1,000 300 3,218 1,500 1,869 444 0 1,360 3,500 300 10,000 Q3: Regarding your answer to Q2, please select the most accurate statement. ANSWER CHOICES PERCENTAGE RESPONSES The number is based on a comprehensive inventory of rock slopes across our entire highway system. 32.26 10 The number is based on a partial inventory of our state’s rock slopes. If selecting this statement, please enter the approximate percentage (0 to 100) of the roadways inventoried in the field, below. 25.81 8

Survey Responses 61   The number is an estimate based on experience. 41.94 13 Total 31 Percentages cited: 75, 1, 1, 0, 50, 100, 85, 0, 100, 95, 3, 90, 20, 0, 100, 100, 20, 100, 25, 50, 90, 100, 20, 90. Q4: Considering all your rock slopes, please estimate a percentage that fits the criteria in the table. Please fill in the approximate percentage (0 to 100 scale, adding up to 100) for each category. Approximate percentages based on recollection (±10%) are okay. ANSWER CHOICES AVERAGE NUMBER TOTAL NUMBER RESPONSES Rock slopes that have not required maintenance or produced rockfall hazards since original construction. 39 1,258 32 Rock slopes that have produced rockfall and required periodic maintenance (i.e., non-emergency ditch cleaning). 40 1,275 32 Rock slopes that have rockfall mitigation measures installed and are functioning as originally designed. 7 230 32 Rock slopes that have rockfall mitigation measures installed but measures are not functioning as originally designed. 2 75 31 Rock slopes that have been reconstructed or minorly realigned in the past 25 years using modern design approaches and guidance (controlled blasting techniques, rockfall catchment ditches, benching, etc.). If these newer slopes can be categorized as a rockfall problem as per response 3 or 4, include them there. 7 205 29 Rock slopes that have been newly constructed for a new roadway or major realignment in the past 25 years using modern design approaches and guidance. If these newer slopes can be categorized as a rockfall problem as per response 3 or 4, include them there. 5 157 29 Q5: Considering the engineering design of new rock cut slopes in the past 20 years, please estimate a percentage that best describes the designer’s affiliation. Please fill in the approximate percentage (0 to 100 scale, adding up to 100) for each affiliation. Approximate percentages based on recollection (±10%) are okay. ANSWER CHOICES AVERAGE NUMBER TOTAL NUMBER RESPONSES Design services provided by agency in-house professionals 46 1,412 31

62 Design Practices for Rock Slopes and Rockfall Management Design services provided by consultants 51 1,570 31 Design services provided by a construction contractor 9 217 23 Design services provided by a manufacturer 0 1 23 Q6: Considering the design of rockfall mitigation measures in the past 20 years, please estimate a percentage that best describes the designer’s affiliation. Please fill in the approximate percentage (0 to 100 scale, adding up to 100) for each affiliation. Approximate percentages based on recollection (±10%) are okay. ANSWER CHOICES AVERAGE NUMBER TOTAL NUMBER RESPONSES Design services provided by agency in-house professionals 48 1,581 33 Design services provided by consultants 46 1,463 32 Design services provided by a construction contractor 8 232 28 Design services provided by a manufacturer 1 24 25 Part D: Design Standards Q1: Has your agency developed minimum design standards guiding rock slope and/or rockfall mitigation? Examples could include ditch containment percentages, minimum ditch widths, frequency of rockfall reaching the road, or maintenance objectives. ANSWER CHOICES PERCENTAGE RESPONSES Yes, formal standards have been developed and documented. 42.42 14 Yes, standards have been developed but not documented as formal department policy. 15.15 5 Yes, informal standards have been communicated between agency geotechnical personnel. 15.15 5 Yes, informal standards that may be applied on a project-specific basis. 12.12 4 No, but we are considering formal, documented design standards. 0 0 No, we have no design standards, but we use consistent approaches to develop rock slope and rockfall mitigation designs. 15.15 5 Total 33 Comments:

Survey Responses 63   Standard drawing RD11-S-11B is [roadway] designer guidance, but there are notes on the sheet that advise seeking geotechnical advisement on most matters. 95% rockfall catchment in ditches is an unofficial design standard we use. We follow published guidelines and standards but have the benefit of risk acceptance for site-specific locations, plus there is the fact that each partner agency (USFS, NPS, etc.) has different expectations. Only for use of RCAD; no policy for % catchment. DRAWING E 102.1.0 [. . .].gov/doc/construction-standard-details/download Informal standards have been applied on some projects, but consistent approaches are used to develop designs on all projects. Typically use [RCAD] guide for guidance. Refer to [. . .] Geotechnical Bulletin 3. Design standards have been developed and are in use; department policy revision is under way. Specific in fence/catchment design when possible for mitigation. Not specific when draping, meshing, attenuating without changing slope/catchment geometry. We provide standard designs and project-specific designs as a specialty office for projects that request our assistance. Detailed in [. . .] DOT Pub. 293, Ch. 8 Rock Cut Slope and Catchment Design. Q2: If formal or informal standards are in use, do they vary between new cut design and rockfall mitigation on existing slopes? ANSWER CHOICES PERCENTAGE RESPONSES Yes, design standards are unique between designs for new cuts and rockfall mitigation. 46.88 15 No, rock slope design standards are the same for rockfall mitigation as they are for new cuts. 25.00 8 No, we only have design standards for rockfall mitigation. 0 0 No, we only have design standards for new cut slopes. 15.63 5 Not applicable; we do not have rock slope or rockfall design standards. 12.50 4 Comments: See comment about partner agencies; they are all different. It is mostly a judgment call by the designer. There are no rockfall standards. New cuts should be evaluated as well, regardless. Because we are balancing resource needs, rockfall mitigation is often considered an improvement for risk reduction, whereas new rock cuts are generally considered to meet informal industry standards.

64 Design Practices for Rock Slopes and Rockfall Management We have the same standards (catchment width, etc.) but acknowledge that there are differences in how you address issues depending on if it is a new cut or mitigation. New cuts are typically designed to a higher standard because they are part of larger higher-dollar projects. Mitigation projects are typically confined to existing R/W and highway templates. Typically, formal standards for new cuts and cut revisions/mitigation require minimal design standards or nonstandard options (site specific). Q3: If formal or informal standards are in use, do they vary between roadway classifications or other particulars? ANSWER CHOICES PERCENTAGE RESPONSES Yes, separated by highway functional classification (interstate, major arterial, minor collector, etc.). 15.15 5 Yes, between highway system designation (National Highway System [NHS], state highway system, etc.). 3.03 1 Yes, separated by average daily traffic (ADT) volume. 6.06 2 Yes, separated by another metric (describe below). 18.18 6 No, rock slope design standards are consistent across roadway classifications. 42.42 4 Not applicable; we do not have rock slope or rockfall design standards. 15.15 5 Comments: General Note on RD11-S-11 states seek advisement from geotechnical agency if rockfall catchment ditch width cannot be achieved. We’re pushing the USMP format out to NPS. Popular roads get the most attention, YOSE and the big parks with packed roads. Done informally and is a judgment call by the designer. Site specific would better describe the entire state’s approach. Design also depends on rockfall frequency and funding. We typically have different standards for our different partners we work for (state DOT, county, federal partner considerations). We base this on both ADT and rock face height. In theory, no. Practically, the secondary system is far more customized due to lower speeds, ADT, etc. The goal of the informal standards is the same, but given budget restrictions, lower-volume secondary roads often end up being designed to a lower standard. Separated by interstate versus state route. Except that we provide a relative risk rating for rock slopes based on traffic volumes. Soft metrics (factors such as available funding, criticality of the road) will influence the ultimate design for a given slope.

Survey Responses 65   Q4: Does your agency apply these standards to other appurtenant facilities, such as pedestrian trails, maintenance facilities, bridge abutments, and so forth? ANSWER CHOICES PERCENTAGE RESPONSES Yes 30.30 10 No 36.36 12 Not applicable 33.33 11 Comments: NPS staff buildings. They frequently are, but they are not supposed to. Bridge abutments would be specific design. We have no standards for these other situations. Q5: Approximately what year were standards adopted? If question is not applicable, please enter N/A. Responses (N/As excluded): 1998, 2016, 2012, Informal adoption of RCAD in 2002, 2005, 1995, 2001, the only standard is informal % containment—1995, 2010 is the first year I can find it, but it may be older, N/A or pre-1988, 2005, 2006, 2000, Informal standard in 2002 (after ODOT Rockfall Catchment Area Design Guide published), 2017, 2016, 1985, It has been an evolving process since the development of the Rockfall Catchment Area Design Guide in 2001, +/-1985, 1988, 2008, 2018. Q6: Design standards may vary between various highway classifications (e.g., functional classification, NHS versus state highway systems). Please outline your design standards, formal or informal, for one of two classifications. If more than two apply, please contact the principal investigator. Enter values to the applicable descriptor per classification. Values can be left blank when they do not apply, and many agencies may enter only one or two values. An example response is shown following question 7. ANSWER CHOICES PERCENTAGE RESPONSES Classification 100.00 22

66 Design Practices for Rock Slopes and Rockfall Management • State or interstate • Slope Rating Form (USMP) • Interstate • All primary highways (interstate, U.S., and state) • Interstate • All state roadways • Federally funded (FHWA) ER [Emergency Response] projects • Interstate • State or county partner • State highway system (no differences in standards for any classification) • National • Rock slope design along interstate or high ADT state divided highway • Interstate Highway System • New primary two-lane U.S. or state highway • Rockfall mitigation along trunk highways • All • Interstate/parkways (when full safety is required) • All roads • Interstate routes • All • New rock cut Percentage of rockfall contained by roadside ditch. (N/As not included.) • 90 • 3 (USMP score) • 100 (i.e., no rockfall in pavement) • 90 • 0 (rarely use) • 95–98 • 90 • 95 • 90 • 95 • 90 81.82 18

Survey Responses 67   • 90–95 • 95 • 90 • 98 • 95 • 90 Percentage of rockfall impacting in roadway ditch. (N/As not included.) • 95 • 27 (USMP score) • 100 • 100 • 99 • 99 • 99 • Not considered independently • 99 • 90 • 97 59.09 13 Percentage of reduction of rockfall reaching the road. (N/As not included.) • 100 • 95 • 95 • 90 • Less than 5 54.55 12 Roadside ditch width. (N/As not included.) • 21' minimum • 3' (USMP score) • As per specific design • 10' • Typically controlled by highway geometrics and ROW • RCAD guidance or state requirements used • Varies based on geometry of slope and ditch • Based on ODOT Rockfall Catchment Area Design Guide 72.73 16

68 Design Practices for Rock Slopes and Rockfall Management • Adopted roadway template is 10'. Not a specific function of Geotech. Geotech may add additional width as catchment. • Dependent on rock slope height, cut angle, and discontinuities • Minimum width, Green Book clear zone • 18' minimum • Clear zone or drainage dependent • Per ODOT Rockfall Catchment Area Design Guide/Ritchie ditch • 10' minimum Target “scoring” of evaluation systems (RHRS, condition assessments, etc.). Comment below on the system used. (N/As not included.) • RHRS for above 300 • 95% containment • N/A different systems used in different districts • Mitigate slopes with CRHRS [Colorado Rockfall Hazard Rating System] score >650 • RHRS, incidents, and maintenance • RHRS and rockfall modeling • Slopes are scored in GAM system. No adopted target. • N/A; we use a relative risk system. 63.64 14 Frequency of rockfall reaching the roadway. (N/As not included.) • We only get calls when they panic about it. • 0 • 1 every 5 years • Few • Documented for future consideration. No allowable value for consideration otherwise. • Few • 2 times per year 45.45 10 Maintenance activity frequency. (N/As not included.) • Infrequent • What’s maintenance? • 0 • Yearly in spring, or as needed • 3 every year 54.55 12

Survey Responses 69   • Hopefully reduce it; but contain to ditch is the goal. • Informal consideration. Does enter into GAM database. GAM database not currently used. • Low • Infrequent • Annual Probabilistic measure (impedance, accident, etc.) (N/As not included.) • <1% • Okay if predicted to impede shoulder but not actual travel lane (uses paved shoulder as catchment width). 31.82 7 Other: • Rock excavation slope 0.25 to 1.0 (H:V) with presplitting • This was not listed as a standard because it was only used specifically for the 2013 Flood Response. • Reduce direct impacts and minimize rockfall reaching the roadway, especially the larger rocks on these higher-volume roads. 18.18 4 Other: • Rock excavation slope 0.50 to 1.0 (H:V) with no presplitting 9.09 2 Q7: Please outline your design standards, formal or informal, for two of two classifications. If more than two apply, please contact the principal investigator. Enter values to the applicable descriptor per classification. Values can be left blank when they do not apply, and many agencies may enter only one or two values. An example response is shown following this question. ANSWER CHOICES PERCENTAGE RESPONSES Classification • Primary • NHS and major state highways • Primary highway • Federal Land Management partner • State • State highway system

70 Design Practices for Rock Slopes and Rockfall Management • Secondary roadway mitigation • U.S. or state route • Non-Interstate routes • Existing rock cut Percentage of rockfall contained by roadside ditch. (N/As not included.) • 100 (i.e., no rockfall in pavement) • 90 • 92–95 • 85 • 95 • Noted, not formally assessed. Modeled if fence catchment is desired mitigation approach: 90. • Varies • 95 • 80 90.91 10 Percentage of rockfall impacting in roadway ditch. (N/As not included.) • 99 • 99 • Noted, not formally assessed. Modeled if fence catchment is desired mitigation approach: 90. • 10% 54.55 6 Percentage of reduction of rockfall reaching the road. (N/As not included.) • 100 • 95 • 95 • Modeled if fence catchment is desired mitigation approach. • 50 54.55 6 Roadside ditch width. (N/As not included.) • As per specific design • RCAD guidance • May be modeled if borderline acceptable as is. • 12' or 14' minimum • Per ODOT Rockfall Catchment Area Design Guide/Ritchie ditch 100.00 11 • 6' minimum 63.64 7

Survey Responses 71   Target “scoring” of evaluation systems (RHRS, condition assessments, etc.). Comment below on the system used. (N/As not included.) • N/A; different systems used in different districts • RHRS, incidents, and maintenance • RHRS and rockfall modeling 45.45 5 Frequency of rockfall reaching the roadway. (N/As not included) • Few to some • May be modeled if determined to be warning of larger- scale future event. • 2 times per year 45.45 5 Maintenance activity frequency. (N/As not included.) • Hopefully reduce it; but contain the big rocks to the ditch is the goal. • Low • Annual 45.45 5 Probabilistic measure (impedance, accident, etc.) (N/As not included.) 18.18 2 Other: • Try to eliminate the direct impacts, and the goal is to improve the rollouts from reaching the travel way when weighing all the needs of our partner’s mission and goals. 18.18 2 Other: • Rock excavation slope 0.50 to 1.0 (H:V) with no pre- splitting 9.09 1 Part E: Design Practice Q1: Please rank the relative importance, with 1 being the most important and 5 being the least, of the following technical considerations for new cut slopes. Equal factors can be given the same number. Please consider each design purpose independently and state agency viewpoints to the extent possible. ANSWER CHOICES Most Important: 1 2 3 4 Least Important: 5 Total Project delivery method (design– bid–build, CM/GC [Construction Manager/General Contractor], design–build) 3 4 9 6 10 32

72 Design Practices for Rock Slopes and Rockfall Management Constructability 23 5 3 1 0 32 Construction funding sources versus maintenance funding sources 7 10 7 6 2 32 Long-term maintenance 13 13 5 1 0 32 Asset management 5 6 12 6 1 30 Aesthetics 3 10 9 5 5 32 Life-cycle costs 2 19 6 2 2 31 Resilience initiatives 2 8 12 5 4 31 Risk management plans 5 8 12 3 2 30 Other: 1 0 2 0 0 3 Comments: Roadway design and alignment generally drive the slope design, and geotechnical considerations override only when issues are too large to readily overcome cheaply. The question or some of the categories are not clear or not understood. No general risk management plans but very focused on slope-specific risk. Q2: Please rank the relative importance, with 1 being the most important and 5 being the least, of the following technical considerations for rockfall mitigation. Equal factors can be given the same number. Please consider each design purpose independently. Please state whether the responses are personal or agency viewpoints. ANSWER CHOICES Most Important: 1 2 3 4 Least Important: 5 Total Project delivery method (design– bid–build, CM/GC, design–build) 3 6 8 7 8 32 Constructability 23 6 3 0 0 32 Construction funding sources versus maintenance funding sources 11 9 8 2 1 31 Long-term maintenance 11 15 6 0 0 32 Asset management 5 12 9 3 0 29 Aesthetics 3 11 8 4 5 31 Life-cycle costs 0 21 8 0 2 31

Survey Responses 73   Resilience initiatives 2 13 10 2 3 30 Risk management plans 4 10 11 3 3 31 Other: 0 2 0 0 0 2 Comments: Cost can drive the technical consideration. The question or some of the categories are not clear or not understood. No specific resilience initiatives, but detour and transportation disruption are a strong factor in formal GAM rating. Q3: If aesthetics are considered in rock slope design projects, select the percentage of total rock slope design projects that consider aesthetics. Please describe the reasoning for considering aesthetics (e.g., considered because of internal agency requirements, considered as a result of other agency input). ANSWER CHOICES PERCENTAGE RESPONSES 90%–100% 13 4 75%–90% 13 4 50%–75% 6 2 25%–50% 19 6 Less than 25% 34 11 Not applicable 16 5 Comments: Cultural resource agencies Aesthetics only really come into play when dealing with rock cut remediation in or near towns. Safety should be the main issue. Depends on the partner and their viewshed preferences. Aesthetics are a consideration in all projects. Aesthetics aren’t typically considered by design staff [. . .]. Scenic Merritt Parkway commission requires no pre-split lines in final slope. [. . .] commitment to context-sensitive solutions Balance desires of public, other agencies, and cost. Partner requirements to balance safety and natural resources and visual/cultural significance in the areas we work Less than 1%—very rare (one project inside a state park) Professionalism. High tourist traffic.

74 Design Practices for Rock Slopes and Rockfall Management Department policy; community outreach, environmental concerns [. . .] rock slopes are often through, or border, public lands. Heavy tourism industry. Outside permitting agencies and municipalities typically drive the aesthetic considerations. Many of the rock slopes are within USFS-managed land, and aesthetics are dictated by the USFS. Rock cuts in tourist areas or high-traffic areas Q4: If aesthetics are considered in rock slope design projects, select which methods are utilized to address aesthetic concerns. ANSWER CHOICES PERCENTAGE RESPONSES Staining of steel products 71 20 Contouring of wire mesh/nets to the slope 57 16 Hammering out half casts on cut slopes 21 6 Removing proximal ends of rock bolts 39 11 Other (please specify) 61 17 Comments: Staining shotcrete to match local rock color Vegetated mats, pins that catch debris and destroy the mesh Stained shotcrete or other facing Permeon treatment of rock slope where it was scaled Countersinking rock bolts, introducing projections and appurtenances to provide a more “natural” look Biomechanical stabilizing and using low-visibility mesh Not aware of aesthetics considerations Scarifying drill lines Consideration of alternative mitigation methods (PUR [polyurethane resin]) Rock painting and staining following scaling activities Color of mesh to match slope Limiting overbreak and rockfall Revegetation; colorization of elements; use of natural materials Staining slope shotcrete, slope geometry to either match existing or minimize visual impact. Oddly, adding half casts in shotcrete to match existing intact half casts [. . .]. One of our districts uses a “Rustic Slope” special provision. Choosing the least visible option Sculpt and stain shotcrete

Survey Responses 75   Q5: Please rank the relative importance, with 1 being the most important and 5 being the least, of the following risk considerations for new cut slopes. Equal factors can be given the same number. Please consider each design purpose independently and state agency viewpoints to the extent possible. ANSWER CHOICES Most: 1 2 3 4 Least: 5 Total Consequence of minor slope failure (minor rockfall, occasional rock on the road, etc.) 7 17 5 4 0 33 Consequence of major slope failure (rock debris blocking the road, frequent rockfall with blind corners and high traffic, etc.) 31 1 0 0 1 33 Maintenance frequency and associated costs 4 17 10 1 0 32 Risk reduction through visual monitoring (site visits without instrumented monitoring) 2 9 8 10 3 32 Risk reduction through instrumented, automated monitoring 0 4 2 14 12 32 Fiscal impacts of poor performance 4 14 10 2 2 32 Liability concerns related to poor performance 11 11 2 6 2 32 Risk acknowledgment and sharing between designer, owner, and contractor 6 7 7 4 8 32 Q6: Please rank the relative importance, with 1 being the most important and 5 being the least, of the following risk considerations for rockfall mitigation. Equal factors can be given the same number. Please consider each design purpose independently and state agency viewpoints to the extent possible. ANSWER CHOICES Most: 1 2 3 4 Least: 5 Total Consequence of minor slope failure (minor rockfall, occasional rock on the road, etc.) 10 15 4 4 0 33 Consequence of major slope failure (rock debris blocking the road, frequent rockfall with blind corners and high traffic, etc.) 26 5 1 0 1 33 Maintenance frequency and associated costs 9 13 9 1 0 32 Risk reduction through visual monitoring (site visits without instrumented monitoring) 2 11 12 5 2 32 Risk reduction through instrumented, automated monitoring 1 2 4 13 12 32 Fiscal impacts of poor performance 5 14 7 4 1 31

76 Design Practices for Rock Slopes and Rockfall Management Liability concerns related to poor performance 10 13 2 7 0 32 Risk acknowledgment and sharing between designer, owner, and contractor 7 6 7 6 6 32 Q7: Please evaluate the relative frequency of use for the following technical design tools. Please fill in the approximate percentage each design tool is used for design of new cut slopes when rock is exposed in existing cuts. For example, if all new rock slope projects characterize the rock mass using rock mass ratings (RMRs), 100 would be entered. Approximate percentages based on recollection (±10%) are okay. ANSWER CHOICES AVERAGE NUMBER TOTAL NUMBER RESPONSES Surface reconnaissance 97 3,190 33 Rope-based reconnaissance 15 478 32 Geotechnical drilling 58 1,900 33 Geotechnical instrumentation 10 326 33 Geophysical methods 26 848 33 Specialized rock laboratory testing (unconfined compressive strengths, petrographic analysis, discontinuity sliding friction, JRC, JCS, etc.) 40 1,306 33 Oriented borehole imagery or oriented coring 13 400 31 Rock mass characterization methods (RMR, SMR, GSI, RQD, etc.) 69 2,280 33 Stereonet and kinematic analyses 57 1,897 33 Deterministic slope stability models 44 1,325 30 Probabilistic slope stability models 27 755 28 Photogrammetric or laser scanner–derived point cloud analysis 28 896 32 2-D Rockfall modeling and containment percentage calculations 60 1,925 32 3-D Rockfall modeling and containment percentage calculations 8 260 32 Design guides (i.e., Rockfall Catchment Area Design Guide) and containment percentage calculations 83 2,665 32 Comments: Often, multiple methods are used (i.e., stereonets are always evaluated, and RMR is always assessed). Geologic maps, well drilling logs Generally, new cuts would be accompanied by a report with recommendations. Smaller cuts might just follow the construction standards.

Survey Responses 77   Q8: Please evaluate the relative frequency of use for the following technical design tools. Please fill in the approximate percentage each design tool is used for design of new cut slopes when rock is minimally or not exposed in existing cuts. Approximate percentages based on recollection (±10%) are okay. ANSWER CHOICES AVERAGE NUMBER TOTAL NUMBER RESPONSES Surface reconnaissance 90 2,709 30 Rope-based reconnaissance 5 151 28 Geotechnical drilling 82 2,449 30 Geotechnical instrumentation 16 458 28 Geophysical methods 46 1,391 30 Specialized rock laboratory testing (unconfined compressive strengths, petrographic analysis, discontinuity sliding friction, JRC, JCS, etc.) 55 1,646 30 Oriented borehole imagery or oriented coring 21 613 29 Rock mass characterization methods (RMR, SMR, GSI, RQD, etc.) 81 2,424 30 Stereonet and kinematic analyses 42 1,231 29 Deterministic slope stability models 46 1,230 27 Probabilistic slope stability models 31 766 25 Photogrammetric or laser scanner–derived point cloud analysis 13 353 28 2-D Rockfall modeling and containment percentage calculations 50 1,498 30 3-D Rockfall modeling and containment percentage calculations 2 55 27 Design guides (i.e., Rockfall Catchment Area Design Guide) and containment percentage calculations 85 2,370 28 Comments: Geologic maps, well drilling logs This category does not appear to apply as it seems to be associated with an entirely new roadway alignment and would be rare for [. . .] DOT. Q9: Please evaluate the relative frequency of use for the following technical design tools. Please fill in the approximate percentage each design tool is used for design of rockfall mitigation. Approximate percentages based on recollection (±10%) are okay. ANSWER CHOICES AVERAGE NUMBER TOTAL NUMBER RESPONSES Surface reconnaissance 99 3,179 32

78 Design Practices for Rock Slopes and Rockfall Management Rope-based reconnaissance 21 654 31 Geotechnical drilling 27 876 32 Geotechnical instrumentation 7 197 30 Geophysical methods 18 572 32 Specialized rock laboratory testing (unconfined compressive strengths, petrographic analysis, discontinuity sliding friction, JRC, JCS, etc.) 30 931 31 Oriented borehole imagery or oriented coring 6 184 30 Rock mass characterization methods (RMR, SMR, GSI, RQD, etc.) 55 1,640 30 Stereonet and kinematic analyses 53 1,651 31 Deterministic slope stability models 42 1,085 26 Probabilistic slope stability models 29 706 24 Photogrammetric or laser scanner–derived point cloud analysis 38 1,050 28 2-D Rockfall modeling and containment percentage calculations 68 2,039 30 3-D Rockfall modeling and containment percentage calculations 5 135 27 Design guides (i.e., Rockfall Catchment Area Design Guide) and containment percentage calculations 75 2,105 28 Comments: Geologic maps, well drilling logs Generally, a significant rockfall would be accompanied by a report with recommendations. Smaller cuts might just follow the construction standards. Use design guides to show how existing slope is out of compliance. Rarely able to mitigate with new design. Use to justify other mitigation techniques and costs if not designing new geometry. Part F: Performance Measures Q1: Does your agency have performance measures specific to rock slopes and/or rockfall management? Performance measures could include number of rockfall events blocking/forcing closure of the road, rockfall patrol frequency by maintenance, closure durations, public contacts regarding rockfall, or other performance-related rock slope issues. ANSWER CHOICES PERCENTAGE RESPONSES Yes, as part of a larger management program. 13 4 Yes, informally tracked by our geotechnical group. 34 11 No 53 17

Survey Responses 79   USMP; relies on partner data and knowledge. Geologists, who are few, have done the monitoring; with some districts having no geologists, little tracking has been done. Performed at our district level. We have a Rockfall Asset Management Plan in place. Our inventory rating is initially based on probability of rockfall occurrence and probability of reaching the road with additional details collected depending on risk level. We are in the process of developing a GAM system for rock slopes. Q2: Does your agency regularly engage in data collection efforts to determine if design standards and/or performance objectives are met? For instance, if a design standard of 90% rockfall containment has been adopted, are rockfall event data collected to confirm that this percentage is achieved? ANSWER CHOICES PERCENTAGE RESPONSES Yes 16 5 No 72 23 Not applicable 13 4 Comments: We’re trying to push the USMP. [. . .] is working to establish performance objectives to meet department asset management and resilience goals. Frequency of reinspection is based on risk rating determined during most recent inspection. We don’t now, but it will be included as a long-term goal in the GAM system. Informally Q3: The synthesis will also include case examples demonstrating unique or mature agency practices and perspectives. The development of the case examples will require an additional follow-up interview via phone or videoconference. Agencies participating in the case examples will be provided with an opportunity to review the case example write-up. The estimated time commitment for your agency for the case example is 1 to 1.5 hours for the follow-up interview. Would your agency be interested in participating in a case example? Comments:

80 Design Practices for Rock Slopes and Rockfall Management Q4: If applicable, what lessons has your department learned regarding rock slope and rockfall mitigation design in the past 10 to 20 years? (Comment only.) Responses Get leadership involved in funding. Obtain buy-in from districts/regions. Maintain good policy documents and don’t waver from them. Unpredictable and should be taken very seriously. [. . .] at [. . .] and [. . .] at [. . .] have the most experience with the USMP, but both are busy as can be, so I won’t volunteer them for this. Suggest you reach out to them directly. Rock slopes must be considered geotechnical assets so that a funding stream for design and maintenance can be assured. Rock slopes must be inventoried. Rock slopes must be managed according to some verifiable metric. Managed expectations and rock slope safety improvements are most important when limited funding is prevalent. Some slopes just can’t be mitigated to meet a specific design standard without spending an incredible amount of money. Good site information (topographic survey, rock stratigraphy, engineering properties of rock, and site drainage) is needed for good design. The design and maintenance experience of other states with more common rock slopes is useful, as provided in technical publications and design guides. [. . .] DOT has no formal rock cut inventory. To the best of my knowledge, there have not been many or any complete rock cut failures. Rockfalls do occur, and some rock does enter the roadway at times. In these cases, catchments are cleaned out, but some falls do occur. Depending on the size and extent, consultants will be engaged to provide recommendations. Yes 45 14 No 55 17 ANSWER CHOICES PERCENTAGE RESPONSES

Survey Responses 81   We have very few significant rock cuts. Our biggest concerns and problems occur when geometric/environment/ROW requirements conflict with rock cut design requirements. Personal follow-up call might be more efficient for this [. . .]. Putting rock slopes into an asset management framework is essential for targeting funding and developing an objective program to address needs. Working with external partners that have different missions and goals has forced us to be flexible and adaptable and has put us in a role of educating our uninformed partners about rock work to following guidance from strong partners that have standards that they would like us to follow. Every job for our partners is an opportunity for us to improve the rockfall hazards and risks, but it often doesn’t meet formal or informal design standards in the industry. We don’t set policy as much as inform partner decision makers about their given situation and provide them different levels of mitigation examples at a certain cost to reduce the risk to support their decision that often requires balancing several missions and goals for their land or transportation agency. And sometimes safety is not paramount in places like the people’s federal lands and on our tribal partners’ lands. There is a need to design solutions that are both appropriate for the site-specific conditions and constructable by contractors located within the region. Ohio has encountered a few issues with out- of-state designers not recognizing the state’s specific geology as well as a lack of interest by out-of- state contractors on mitigation projects requiring specific skills/expertise not readily available in Ohio (such as scaling or drape installation). All of our rock slopes will require some form of periodic maintenance. Utilizing new rock slope design and rockfall mitigation tools helps to reduce the risk of catastrophic rockfall events and also lowers long-term maintenance costs. Thank you for conducting this survey. It is expensive. It is vital to retain some in-house staff who are dedicated to continuous training and can provide direct design, or at least knowledgeable input on rock slope mitigation on behalf of agency ownership and risk. That same staff is valuable for providing that input, as well as value-engineering considerations for new rock slope design and construction. Long-term geotechnical staff is required for retaining, formally or informally, information about rockfall frequency, maintenance, and other institutional knowledge. Long-term outside consultant retention for these things is rarely continuous, and it is often outside the purview of maintenance units to adequately collect and retain the information necessary.

82 Design Practices for Rock Slopes and Rockfall Management Comprehensive site characterization is the most important element of any rockfall mitigation or rock cut design project. Experience in construction is paramount to designers. Agency geological/geotechnical institutional knowledge and familiarity with the state’s geology, infrastructure, and rockfall conditions and inventory of highway rock cut slopes should be maintained as a lead element of all programming, whenever possible. In the case of smaller states, this is much more economically efficient and can speed up the design and implementation of slope construction and mitigation. Whenever possible, agency personnel should also be directly involved in construction, in order to evaluate field conditions, implement changes, and further future considerations. Over the past 10 to 20 years, our department has learned the value of UAV imagery, lidar, and ground-based photogrammetry for evaluating, constructing, and monitoring rock slopes and rockfall mitigation. We have learned that change happens slowly. When we first began recommending rockfall remediation on projects, highway designers and maintenance personnel were skeptical and thought it was a waste of money. Although some of our efforts have been less than successful, there were far more very successful projects, which provided increased safety and reduced maintenance costs. It has taken 20+ years, but now as agency [. . .] DOT sees the importance of rockfall mitigation and it has become a normal consideration in highway projects. We’ve come to rely more often on specialty scaling and rock remediation contractors versus using general contractors. It has been difficult to obtain funding for mitigation as an end in itself and has been much easier to work it into existing projects. UAV surveys are a game changer for designing in areas that are difficult to measure/survey. Important to design mitigation systems for easy maintenance/cleaning. A good way to do this is to have the designers consult with the people who will be responsible for maintenance.