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Estimating and Contracting Rock Slope Scaling Adjacent to Highways (2020)

Chapter: Chapter 3 - State of the Practice

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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
×
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Suggested Citation:"Chapter 3 - State of the Practice." National Academies of Sciences, Engineering, and Medicine. 2020. Estimating and Contracting Rock Slope Scaling Adjacent to Highways. Washington, DC: The National Academies Press. doi: 10.17226/25824.
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11 The state of the practice detailed in this synthesis was gauged with a questionnaire designed for completion in about 30 minutes. The questionnaire was administered with an Internet- based survey tool and disseminated to lead geotechnical personnel in all 50 states; Puerto Rico; Washington, D.C.; and the Western, Central, and Eastern divisions of the Office of Federal Lands Highway. Requests for questionnaire responses were made through e-mail, follow-up e-mails, and telephone calls. The questionnaire was subdivided into six categories focusing on (1) administering scaling projects, (2) design efforts, (3) plans and specifications, (4) administering construction activi- ties, (5) scaled slope performance, and (6) lessons learned. Each category included several ques- tions, for a total of 31 scaling-specific questions. The state of the practice for each category is described in the following sections. Appendix A contains the questionnaire, and Appendix B contains response data. Questionnaire Respondents Responses were provided by 42 DOTs and two Federal Lands Highway division offices— an 80% DOT response rate. Because not all areas possess the topography and geology to benefit from slope scaling, the survey incorporated two questions that permitted responses while not requiring excessive time. Of the 44 total respondents, 24 of those performed enough scaling to respond to the more detailed questions. These 24 responding DOTs and Federal Lands High- way division offices are termed “scaling states” in the body of this synthesis. Figure 4 presents a map of these respondents. Administration of Scaling Scaling projects are often selected using a variety of methods—some planned and some unplanned. Requesting the approximate proportions of project selection methods, the survey indicated that states used two primary project selection approaches for identifying eligible sites and following through with the scaling work. Responding departments indicated that scaling projects were selected either through a programmed project selection process, at 37% (e.g., a Statewide Transportation Improvement Program [STIP], through a Highway Safety Improve- ment Program [HSIP]), or through being performed as part of an emergency response following rockfall events, at 34%. Figure 5 plots survey responses. Notably, all but one responding depart- ment indicated that they did have some proportion of scaling work that was administered on an emergency basis. C H A P T E R 3 State of the Practice

12 Estimating and Contracting Rock Slope Scaling Adjacent to Highways Two other noteworthy departures from this approach are two states that, either statewide or regionally, treated scaling mainly as a maintenance activity; those two jurisdictions (California and Idaho’s District 6) are highlighted in the case examples section. For contractor qualifications, responding state DOTs and federal land management agencies required qualifications for more than 75% of their scaling projects, and 20% were contracted without qualifications. Nearly half of respondents indicated that the scaling contractor that met the qualification requirements was hired by a general contractor (Figure 6). The qualifications that the contractor needed to meet were defined in the specifications. Selection based solely on low bid without qualifications was practiced in only one state, while three other states split their proportion of scaling contracts without qualifications between an on-call contractor for emergency response and a scaling subcontractor hired by a general con- tractor without qualification requirements. Of the 24 scaling states, four states contracted all scaling work without any qualification requirements. Of the remaining 20, four additional states contracted between 5% and 40% of their scaling work without qualification requirements. Figure 4. Map of survey respondents. Figure 5. Survey responses for project selection methods. 1. Programmed as part of an STIP, HSIP, or other statewide or regional project candidate 2. Performed on an emergency basis following rockfall events 3. Performed as part of other highway preservation work (paving, minor realignments, major ditch rehabilitation, guardrail replacements, etc.) 4. Performed as a routine maintenance exercise and/or part of a maintenance program 5. Other Number of respondents n = 24 36.5 34.1 19.0 8.8 1.7 1 2 3 4 5 0 20 40 60 80 100 PE RC EN TA G E

State of the Practice 13 Design Efforts for Scaling Current publications regarding scaling did not have design criteria outlining how to estimate scaling efforts, debris quantities, or the types of efforts recommended for designing scaling plans and specifications (Andrew et al., 2011; Andrew and Pierson, 2012; Pierson and Vierling, 2012). Other recent publications focused on one geographic area with a unique practice and did not contain data sufficient to build a nationwide data set for scaling metrics (Duffy, 2018). The questionnaire focused on gauging approaches to determining level of effort for scaling design, cost estimation efforts, units of measure, and production rates considered “reasonable” by DOTs. Nearly all scaling state DOTs appeared to begin design efforts by using roadside visual review (Figure 7). Maintenance input, providing day-to-day information on location and frequency of rockfall activity and efforts for ditch maintenance, was used by nearly 60% of scaling states. It is important to note that some state maintenance management systems and similar systems may be a data source that is infrequently tapped by geotechnical personnel, but often contains data on rockfall occurrence (Beckstrand and Mines, 2017). Relatively new techniques involv- ing photogrammetry or terrestrial lidar scanning were used for nearly 42% of scaling states (Figure 7). Notes and interviews indicated that the use of this technology was increasing, with at least one state (Tennessee) indicating that surveys obtained before and after scaling would be used to measure pay quantities. Figure 6. Survey responses for use of contractor qualifications, their contracting, and selection. 1. Hired by general contractor with qualification requirements 2. Low bid, qualifications of scalers and/or contractor required 3. Prequalified scaler and/or contractor, on-call list for emergency response 4. Non-prequalified, on-call list for emergency response 5. Hired by general contractor without qualification requirements 6. Low bid 7. Other 45.1 19.0 11.5 10.4 5.6 4.2 4.2 1 2 3 4 5 6 7 0 20 40 60 80 100 PE RC EN TA GE Qualification-based selections Non-qualification-based selection n = 24 1. Roadside visual review by department or consultant geotechnical design personnel 2. Maintenance activity and observations 3. Up-close slope inspection by personnel in boom lifts, in crane baskets, or on ropes 4. Advanced laser scanning and/or photogrammetric techniques 5. Other n = 24 95.8 58.3 54.2 41.7 20.8 1 2 3 4 5 0 20 40 60 80 100 PE RC EN TA G E Figure 7. Design efforts for scaling.

14 Estimating and Contracting Rock Slope Scaling Adjacent to Highways For estimation of scaling debris such as loose rock, soil, and vegetation, there were no published guidelines or data to help DOTs estimate the volume of debris, or the data set was too narrow to apply nationally (Andrew et al., 2011; Andrew and Pierson, 2012; Duffy, 2018; Pierson and Vierling, 2012). Scaling states relied heavily on expert judgment for estimating scaling debris according to rock type and quality, with two-thirds of the responses indicating as much (Figure 8). Others used either volume and area relationships (37%) or relationships between volume or weight and scaler production rates. Seven states (30% of scaling states) used expert judgment to develop volume and area relationships, while two states used expert judgment to develop debris removal estimates based on scaler production rate. One state used weight and area relationships. The most common method to measure and pay for scaling was through hours (68%, dis- cussed later). To develop an estimate, the engineer is required project the number of scaling hours. A scaler’s production rate will depend on the slope’s characteristics, access methods, and experience levels and will require estimation by the engineer. Again, scaling states relied heavily on expert judgment to estimate the production rate, with all but two states using expert judgment for individual slopes or for various levels of effort (Fig- ure 9). The two scaling states that did not use expert judgment either (1) paid a lump sum or according to time and materials, or (2) paid according to surface area covered (e.g., square yard). Two states incorporated an analytical approach using rock quality index systems. 1. Expert judgment for individual slopes 2. Expert judgment for various scaling levels of effort 3. Other 4. Standard quantity for all slopes 5. Analytical approach using rock quality indicators (RMR, RQD, GSI, etc.) n = 24 75.0 54.2 29.2 8.3 8.3 1 2 3 4 5 0 20 40 60 80 100 PE RC EN TA G E Notes: RMR = rock mass rating; RQD = rock quality designation; GSI = geological strength index. Figure 9. Methods for estimating scaler production rates. 1. Expert judgment for rock type and rock quality 2. Volume and area relationships (e.g., ½ yd3 per 100 ft2 of slope to be scaled) 3. Other 4. Unit (vol./weight) production per scaler hour (e.g., ½ yd3 per scaler hour) 5. Weight and area relationships (e.g., 1 ton per 100 ft2 of slope to be scaled) n = 24 66.7 37.5 20.8 16.7 4.2 1 2 3 4 5 0 20 40 60 80 100 PE RC EN TA G E Figure 8. Methods for estimating scaling debris.

State of the Practice 15 The questionnaire requested production rates that were considered “reasonable” by expe- rienced design personnel. For consistency between geologic materials and project purposes, the respondents were asked to presume a non-presplit rock slope; a rock quality designation (RQD) of 60%; and scaling work that was part of a larger rockfall mitigation project within a two-lane, rural, mountainous highway corridor, with scaling performed using rope access methods. Traffic control and its start/stops were ignored but play a significant role in actual daily production rates. Nearly half responded that production rates were too variable to provide an answer (Fig- ure 10). Of those that did respond with rates, half responded that 50 to 200 square feet per scaler hour (not crew hour) was considered reasonable, while the remaining respondents were evenly split between 200 to 400 square feet per hour and 400 to 800 square feet per hour. None responded with greater than 800 square feet per hour, and no comments were received indicating that less than 50 square feet per hour was reasonable. Plans and Specifications for Rock Slope Scaling The plan sheets and specifications may vary significantly among states and among projects. The questionnaire requested information for units of measure (Figure 11), separation of scaling efforts/types into different bid items, methods for illustrating required scaling areas, performance criteria, scaler qualifications, and other details. Samples of plans and specifica- tion packages, some accompanied by redacted contractor submittals, voluntarily submitted by DOTs, are contained in Appendices C and D, respectively. Pay Items Of scaling states, 67% used hours, either crew hours at 50% (crew sizes are typically defined in the specifications) or individual scaler hours. Volume of scaled material was used in three scaling states. Fifty percent of scaling states used separate bid items for different scaling techniques. The number of separate bid items and the details required during construction administration were not examined in detail. Comments and follow-up interviews indicated that the typical separation occurred when heavy equipment (e.g., excavators or cranes) was used. When paying hourly, clarifying when scaling “starts” in the specifications will help reduce potential confusion or disputes. Individual scalers are frequently capable of performing other Figure 10. Production rates considered “reasonable” for general scaling by scaling states. 1. Too variable to answer 2. 50–200 square feet per individual scaler hour 3. 200–400 square feet per individual scaler hour 4. 400–800 square feet per individual scaler hour 5. 800+ square feet per individual scaler hour n = 23 Note: Traffic control start/stops ignored. 47.8 26.1 13.0 13.0 0.0 1 2 3 4 5 0 20 40 60 80 100 PE RC EN TA G E

16 Estimating and Contracting Rock Slope Scaling Adjacent to Highways rockfall mitigation duties, and as such may change roles midday. Questionnaire results indi- cated a wide range of common practices when paying hourly (Figure 12), but most responses indicated that hourly scaling started when the individual or crew began ascending the slope, or starting at the beginning of the shift. Other states waited until the scalers were in position and ready to scale (e.g., suspended on ropes on the rock face). Tasks that were considered payable as scaling hours included the non-scaling foreman, tree/ vegetation removal, labor to support scaling, bench cleaning, and safety spotters (Figure 13). These tasks often require similar levels of training and safety consciousness as those required for slope scaling itself. Typically, scaling extents are shown in the contract plans. However, once scaling commences, a scaling contractor may request payment for scaling outside the specified boundaries. Worker safety was often cited as the primary rationale. The most common practice (42% of scaling state respondents) was to respond on a case-by-case basis, typically responding to requests with additional investigation and evaluation by geotechnical personnel (Figure 14). Payment at the contract rate was used with nearly the same frequency. Other agencies either considered safety scaling incidental or paid at a new negotiated rate. Comments indicated the sensitivity of the subject. In general, the consensus was that if it appeared to be for the contractor’s convenience, it was incidental, but if it was an agreed safety concern, it was a paid effort. Payment for removal and hauling of scaling debris was handled mainly by unit volume removed, typically measured by truck counts (Figure 15). 1. Hours (crew hours) 2. Hours (individual scaler hours) 3. Unit volume 4. Other 5. Unit area 6. Unit length 7. Lump sum n = 24 50.0 16.7 12.5 12.5 8.3 0.0 0.0 1 2 3 4 5 6 7 0 20 40 60 80 100 PE RC EN TA G E Figure 11. Units of measure for scaling activities. Figure 12. When hourly scaling starts, if paying hourly. (“Not applicable” answers excluded.) 1. When ascending (e.g., via hiking, boom lift, helicopter, etc.) to the top of the slope 2. Beginning of the shift 3. When in position and actively scaling using the allowed scaling methods 4. Other 5. When ascending the slope while harnessed up n = 2427.8 27.8 22.2 16.7 5.6 1 2 3 4 5 0 20 40 60 80 100 PE RC EN TA G E

State of the Practice 17 Figure 13. Tasks that are measured and paid as scaling. 1. Labor to support scaling/equipment moving (air hoses, ropes, etc.) while not harnessed up 2. Non-scaling foreman 3. Tree/vegetation removal at the slope crest and/or on the slope 4. Bench cleaning 5. Safety spotters 6. Other n = 23 65.2 65.2 60.9 47.8 43.5 17.4 1 2 3 4 5 6 0 20 40 60 80 100 PE RC EN TA G E Figure 14. Payment for “safety scaling”; scaling requested by the contractor outside the specified plan limits. 1. Case by case 2. Pay it at the contract rate 3. It is considered incidental 4. Other 5. Pay at a new, negotiated rate n = 2441.7 37.5 12.5 8.3 4.2 1 2 3 4 5 0 20 40 60 80 100 PE RC EN TA G E Figure 15. Units of measure and payment for removal of scaled debris. 1. Unit volume removed 2. Other 3. Incidental to scaling 4. Lump sum 5. Time and materials 6. Unit weight removed n = 24 41.7 20.8 16.7 8.3 8.3 4.2 1 2 3 4 5 6 0 20 40 60 80 100 PE RC EN TA GE

18 Estimating and Contracting Rock Slope Scaling Adjacent to Highways A few DOTs indicated that unit volume was measured by lidar scanner or photogrammetry by UAVs. Five DOTs indicated that they typically used a combination of measures depending on availability of survey equipment, truck scales, or urgent work necessitating the use of time and materials for measurement and payment. Overall, the most common state of the practice was to measure and pay according to those measures rather than requesting lump- sum bid items or making debris removal and haul incidental to scaling. Plan Drawings Communicating the work to be performed is the primary purpose of any construction plan set. For scaling, traditional plans containing line work or isometric drawings may less effectively communicate required scaling work. To overcome the limits of traditional plan sets and to exhibit slope features unique to slope scaling, the questionnaire requested information on the preferred method of exhibiting scaling extents in the plan set. Nearly half of scaling states used oblique photographs with scaling extents shown, while addi- tional states indicated that a combination of plan drawings and photographs was used (Fig- ure 16). Other states used either plan view drawings with scaling extents described by station, or only a tabulated listing of scaling extents shown. Qualifications and Performance Criteria Scaling is an inherently high-risk activity, and hiring qualified, experienced contractors will help mitigate the risk. Without experienced personnel, scaling may be performed inefficiently, unsatis- factorily, or unsafely. Personnel have been fatally injured on highway rockfall mitigation projects (Caltrans, 2014b; “Man Killed in Fall During Rockfall Mitigation Work in Clear Creek Canyon,” 2018; Preston, 2017). The questionnaire asked whether qualifications were required, and if they were, to whom they applied. Four DOTs indicated that they did not have qualification require- ments; 19 of the remaining scaling states indicated that they required qualifications (Figure 17). The qualifications that the scaling contractor was required to have were experienced based, when applicable (Figure 18). One-third of the respondents indicated “Other,” with most indi- cating that more than one of the possible selections, such as number of projects per company or years of scaling work for each scaler, were required. One department adjusted the requirements and included references according to the complexity of the work to be performed. Assessing satisfactory completion of scaling by construction engineering personnel may be challenging for those without a geotechnical background. Specifications that define performance criteria provide contractual tools that can facilitate the outcome intended by the design engineer. Figure 16. Preferred method of displaying scaling extents in plan drawings. 1. Oblique photographs with scaling extents drawn 2. Plan view drawings with scaling station extents shown 3. Other 4. Scaling extents by station in a table n = 24 45.8 20.8 20.8 12.5 1 2 3 4 0 20 40 60 80 100 PE RC EN TA GE

State of the Practice 19 Half of scaling states did not specify performance criteria, while the other half either indicated that they did have performance criteria or that scaling was performed to the satisfaction of the engineer or through site inspection. Specifying Temporary Protection Scaling dislodges large rocks that fall largely uncontrolled to the ground below. The impact forces not only can severely injure anyone struck, but also can damage the roadway and other ancillary infrastructure. Temporary roadway protection protects infrastructure (pavements, guardrails, bridges, etc.), while temporary rockfall protection is intended to protect the public or workers during scaling. Protecting the infrastructure from damage can be advantageous; and in some circumstances (low height, divided highways with traffic control, etc.), scaling can be performed while passing traffic. DOTs were queried on their specification of protection measures, either through performance specifications or through specification of protection measures to be installed. If not properly specified, potentially inadequate protection measures may be installed (Figure 19). More than half of the scaling state respondents used contractor-designed rockfall mitigation for temporary roadway protection (Figure 20). Others used a mix of owner- or contractor- designed mitigation measures, typically depending on the nature of the work, with emergency work depending on contractor designs and programmed work depending on owner designs. One department did not require temporary roadway protection. Similar patterns were evident Figure 17. Scaling qualifications and whom they apply to. 1. All scaling personnel 2. All scaling personnel, but with a training/journeyman provision 3. Not applicable 4. Foremen only 5. For the company as a whole rather than on a person-by-person basis 6. Other n = 24 54.2 20.8 16.7 4.2 4.2 4.2 1 2 3 4 5 6 0 20 40 60 80 100 PE RC EN TA GE Figure 18. Personnel or corporate experience requirements. 1. Hours of experience per qualified scaler 2. Other 3. Not applicable 4. Number of projects for scaling work (per company) 5. Number of years of scaling work (per company) 6. Number of projects completed per scaler 7. References from past clients (per company) n = 24 33.3 33.3 16.7 12.5 4.2 0.0 0.0 1 2 3 4 5 6 7 0 20 40 60 80 100 PE RC EN TA GE

20 Estimating and Contracting Rock Slope Scaling Adjacent to Highways for temporary rockfall protection (Figure 21), with a greater number of DOTs responding that the road was always completely closed, eliminating the need for protection. The questionnaire requested information on the types of temporary protection measures that had proved successful in respondents’ departments, ranging from a cleaned catchment ditch to a moveable rockfall barrier. Choosing from a variety of commonly used temporary protection features, departments indicated whether they had used such measures, whether such measures had failed when used on a standalone basis, or whether those measures were a minor or major component of system success (Table 1). The most common measures were common concrete barriers, but those had failed when used alone. The most successful component was a moveable rockfall barrier, which frequently consists of an engineered, purpose-built rockfall fence system installed on sliding steel plates. Figure 19. Plywood and fence stake rockfall protection for an FAA weather station. Photo courtesy of B. Black. Figure 20. Designer for temporary roadway protection. 1. Contractor designed 2. Designed by owner or their representative 3. Other 4. We do not require temporary roadway protection n = 24 54.2 20.8 20.8 4.2 1 2 3 4 0 20 40 60 80 100 PE RC EN TA GE

State of the Practice 21 Administering Scaling Activities During Construction Administering scaling during construction can require full-time technical specialists to direct scaling efforts, either from the ground or via rope access. This scaling-specific approach is often out of the ordinary compared with other highway construction activities, where construction inspectors or engineers supervise construction with occasional input from technical specialists. Departments responded that they typically used a mix of approaches, with the two most common responses indicating that an inspector was frequently augmented by geotechnical staff, either from the ground or on the slope (Figure 22). Four of the 24 scaling states responded that scaling was inspected only from the ground as a part of other inspection duties; all others indicated they had either full-time or part-time geotechnical assistance during construction. Similarly, departments were questioned regarding the personnel who verify that the scaling has been completed satisfactorily (Figure 23). Half of scaling states indicated that an experienced designer verified completion via an on-slope inspection. Other DOTs indicated that the DOT geologist inspected the slope. Four of the 24 scaling states indicated that personnel without scaling experience approve the final work product. The emergence of terrestrial laser scanning and structure from motion photogrammetry techniques has facilitated a wider range of rock slope analyses and evaluation than previously possible (Abellán et al., 2010; Dunham et al., 2017; Lan et al., 2010; Santana et al., 2012). Recognizing this developing method of rock slope examination, the survey requested informa- tion regarding DOTs’ use of these technologies applied to scaling. Nearly half of scaling states Figure 21. Designer for temporary rockfall protection. 1. Contractor designed 2. Designed by owner or their representative 3. Other 4. We always completely close the road, so rockfall protection for the public is not needed n = 2441.7 20.8 20.8 16.7 1 2 3 4 0 20 40 60 80 100 PE RC EN TA GE Table 1. Temporary protection measures used, and their contribution to a successful system. Note: Number of survey respondents = 22.

22 Estimating and Contracting Rock Slope Scaling Adjacent to Highways 1. Experienced designer with on-slope verification 2. Construction engineer with scaling experience 3. Construction engineer without scaling experience 4. Other 5. Scaling is done when the budget is exhausted n = 24 50.0 45.8 37.5 20.8 4.2 1 2 3 4 5 0 20 40 60 80 100 PE RC EN TA GE Figure 23. Personnel who verify that the scaling has been performed to satisfaction. 1. Inspector reviews from the ground as part of other inspection duties 2. Inspector with rock slope experience (in-house or consultant) reviews performance by accessing the slope via ropes or other slope access technique (i.e., boom lift, crane basket, etc.) 3. Inspector with rock slope experience (in-house or consultant) inspects performance from the ground, full time 4. Other n = 24 75.0 66.7 45.8 25.0 1 2 3 4 0 20 40 60 80 100 PE RC EN TA GE Figure 22. Personnel inspecting and supervising scaling activities on departments’ behalf. either planned to use these techniques or used them at the time of the survey. One-quarter of scaling states were uncertain of the techniques’ use or reliability, and therefore, had not used them. One-third of scaling states had no plans to use such techniques, either because of payment unit of measure (hours) or lack of need (Figure 24). When asked which technique the DOT used for monitoring slope performance following scaling projects, two of 24 scaling states indicated they used newer technology, while another four indicated they were beginning to investigate use of newer technologies. One DOT used UAV-based technology, and one other used terrestrial scanners. The four that were beginning to use technology for performance monitoring reported using both terrestrial scanners and UAV-based photogrammetry. Scaled Slope Performance Traditionally, scaling has been referred to as a temporary measure that may be required again in 2 to 10 years in the absence of additional mitigation measures (Andrew and Pierson, 2012; Pierson and Vierling, 2012). Earlier literature indicated durations ranging from 8 to 15 years for slopes with numerous freeze-thaw cycles to 12 to 15 years for slopes in dry climates (Brawner, 1994). Other references provided a range of 3 to 5 years for minor scaling projects on rock

State of the Practice 23 1. Yes, we plan to use advanced techniques to measure scaling completion and area coverage 2. No plans or current use 3. We’ve considered it, but not sure of its use, reliability, or defensibility 4. Other 5. Yes, we currently use advanced techniques to measure scaling completion and area coverage n = 24 37.5 33.3 25.0 12.5 8.3 1 2 3 4 5 0 20 40 60 80 100 PE RC EN TA GE Figure 24. Use of advanced techniques (laser scanner, photogrammetry, UAV, etc.) for uses related to scaling. Figure 25. Tracking and documenting rockfall events following scaling projects. 1. Yes, but kept informally or through job experience 2. Other 3. No, we do not keep records of rockfall following scaling 4. Yes, and we have documentation we can share n = 2437.5 33.3 20.8 8.3 1 2 3 4 0 20 40 60 80 100 PE RC EN TA GE slopes susceptible to weathering (Wyllie and Mah, 2004). However, these guidelines were based on judgment rather than on analysis of consistent data sets. Actual durations would depend on rock slope characteristics, deterioration rates, rock quality, and performance expec- tations of the rock slopes. To develop durations based on data, robust, spatially distributed record-keeping would be required. The questionnaire requested information regarding whether departments had kept records of rockfall events following scaling. Many departments responded that they kept the informa- tion informally through job experience (Figure 25). A third responded “Other,” and indicated that records were kept through maintenance management systems, state police call-outs, or rockfall management systems. Informal record-keeping has been analyzed for research proj- ects. This suggests that the informal nature of the records may not be a significant hindrance for determining the effective life of scaling (Beckstrand et al., 2017; Mines et al., 2018). Overall, about 10 scaling states appeared to have had data sufficient for analysis. Similarly, just over half of scaling states kept records of slope condition pre- and post-scaling, though some commented that the duration between ratings efforts was longer than they would have liked it to be. Others indicated that the inventory and conditions assessments were on a regional or district basis rather than on a statewide basis.

24 Estimating and Contracting Rock Slope Scaling Adjacent to Highways Lessons Learned At the end of the questionnaire, 18 of 24 scaling states provided input on the lessons learned regarding scaling over the previous 10 to 20 years. The responses covered a wide range of topics, many of which were touched upon in the survey questionnaire and complemented by open-ended responses. Further research, as noted in the final section of this report, would help with resolving some issues, such as project estimation with data-driven guidance. Other items may be resolved through implementing more detailed plans with annotated photography, and through preparing specifications that foresee potential issues and provide solutions. In general, lessons learned are best communicated by those who learned them firsthand; therefore, the responses in the following section are paraphrased from open-ended comments, with only minor clarifications added (indicated with brackets). Note that identifying language, such as state names, has been removed. Overall, the lessons learned fall into five categories, summarized in the following. Qualifications and Experience It is invaluable to have an individual with extensive rock slope experience directing the scaling efforts at a site and determining when scaling is complete. We place a high value on the use of experienced engineering geologists to guide scaling work to reduce the potential for damaging the slope and also for focusing work in targeted areas. Experience submittals often vary in how scaling hours are presented and counted, requiring iterative clarification in order to align with our specification. Scaling operations should be closely monitored and inspected for compliance. Experience is key! Relying on general contractors to perform challenging scaling work has become more dif- ficult, and we are moving toward using specialty contractors. Use qualification-based requirements for all scaling personnel; provide a safe way to train scalers in your specifications to allow for replenishment of industry workers. Best results occur when Geotech (design expert) is on site to use judgment on scaling locations and quantities. Design Estimation The more time and experience you spend prior to scaling to assess the degree of effort for scaling needed, the better the project outcome will be. Build in risk to project (extra contingency) due to unpredictable, variable quantities. We have typically experienced difficulties in the accurate estimation of debris removal quanti- ties despite employing a variety of methods. Although some of the observed variability can be attributed to difficulties in quantifying how rock scales based on its condition, some is likely the result of variation in practice from scaler to scaler. This issue is especially acute on very high slopes. Quantities for scaling can almost never be overestimated. Estimating scaling hours and material quantity is very difficult and varies significantly on every job. Accurate surveying of the existing slope topography is important. Correct catchment design is strived for if space is available on a given project.

State of the Practice 25 [Problems have occurred when] extensive vegetation has obscured some areas of the rock cut, making it difficult to predict actual rock slope conditions, leading to change in design once the vegetation is cleared [or] the rock [ . . . ] is much more weathered/unstable than anticipated, leading to extra scaling time. Plans and Specifications Photo plans are a tremendous aid for bidding and contract administration. Lack of [local] scalers can create $/hr irregularities. Prime contractors are motivated to use earthwork equipment instead of [a scaling subcontractor]. Prescriptive approaches have been effective in managing contract costs. In cases where roadway or feature protection is provided by the contractor, they often are not prepared to provide a level of protection that we, as the owner, feel is adequate. We have chosen crew time as opposed to volume production, mostly because it’s easier for an inspector to record. Require air pillows as mandatory equipment for slope scaling (for general and intensive areas); include safety scaling as incidental to your scaling item. Pay by the scaling hour per scaler, not by the crew hour or by area on the slope. Prefer to separate debris removal, including haul, from the slope scaling bid item because it makes it difficult to follow trends in scaling unit bid prices when the debris removal is part of the equation and may heavily influence the unit prices. Issues During Construction We have [ . . . ] run into the issue of scaling thoroughness, meaning that there have been disagreements between us and the scalers as to deciding on when an area has been scaled to satisfaction. We see quite a bit of variation from project office to project office in how scaling hours are counted; do the hours include accessing the slope? How are traffic control delays accounted for? Is a standby rate applied? [We have had issues] with temporary catchment [and] productivity rates. Long-Term Performance We have found the Maintenance scaling of slopes to be extremely important in improving public safety, [realization of] reduced Maintenance expenses, accelerating emergency openings of highways after storm events, and improved protection to State facilities. Some additional rockfall can be expected and planned for after scaling as the slope re-stabilizes. Ensure that Maintenance knows that it is very important to keep the catchment ditch cleaned out to original design criteria. Scaling is cost-effective rock slope mitigation and can be incorporated in larger projects to take advantage of traffic control.

Next: Chapter 4 - Case Examples »
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Scaling loose rock from highway rock slopes is an important aspect of improving rock slope safety in mountainous areas, according to input from 42 state departments of transportation and two regional divisions of the Office of Federal Lands Highway.

The TRB National Cooperative Highway Research Program's NCHRP Synthesis 555: Estimating and Contracting Rock Slope Scaling Adjacent to Highways documents current rock slope scaling practices adjacent to highways.

An appendices document is also included as part of the publication.

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