National Academies Press: OpenBook

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

Chapter: Chapter 4 - Case Examples

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Suggested Citation:"Chapter 4 - Case Examples." 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 4 - Case Examples." 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 4 - Case Examples." 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 4 - Case Examples." 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 4 - Case Examples." 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 4 - Case Examples." 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 4 - Case Examples." 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.
×
Page 32
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Suggested Citation:"Chapter 4 - Case Examples." 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.
×
Page 33
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Suggested Citation:"Chapter 4 - Case Examples." 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.
×
Page 34

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26 Geotechnical specialists from six state transportation departments were interviewed following completion of the broad state-of-the-practice survey. The states were generally selected based on • Unique practice or perspective on scaling practice; • Regular involvement with rock slope scaling projects along highway corridors; • Depth of experience with generating cost estimates, plan sets, and construction specifications for a variety of rock slope scaling projects; • Depth of experience with developing methods to determine job completion and defining successful performance of a scaled rock slope; and • Ongoing efforts to maintain records of past scaling projects and to track project performance over time. The selected states and their practices are described in the following sections. California Department of Transportation Administration of Scaling The California Department of Transportation (Caltrans) employs a nationally unique scaling program wherein approximately 90% of all scaling performed in the state is accomplished by about 200 specially trained Caltrans maintenance personnel. The personnel who sign up for the scaling program do so voluntarily. The other 10% of the scaling is typically contracted to specialty rock slope contractors who meet stringent qualification criteria. This scaling program is “owned” by Caltrans’s maintenance division, and Caltrans’s geotechnical personnel serve the division as if it were an internal client. Between 2014 and 2018, approximately 180 to 200 indi- vidual scaling projects were carried out under this program. When scaling is performed as part of a capital or programmed improvement project, it is typically associated with structure construction, corridor improvement projects, or other large-scale projects that may have adjacent rock slopes that would benefit from scaling or other rockfall mitigation measures. The nature of the scaling program is split approximately fifty-fifty between routine slope maintenance and emergency response. Caltrans does few HSIP/STIP projects that focus on rock- fall mitigation or rock slope stability; however, this trend may be changing as the department shifts from a primarily reactive program to a more proactive approach by informally incorpo- rating geotechnical assets into its Transportation Asset Management program. Scalers are qualified through Caltrans’s own training program and supplemented through certifications by the Professional Climbing Instructors Association (Caltrans, 2014a). This C H A P T E R 4 Case Examples

Case Examples 27 extensive training includes multiple forms to assist scalers in evaluating slope characteristics, site safety, and anchoring conditions, among other items. Slope assessment forms are reviewed by Caltrans’s geotechnical personnel before scaling activities begin. Plans and Specifications for Scaling Caltrans’s maintenance-driven program calculates time and expenses either on a crew-hour basis or through a volumetric measure of removed debris. Typically, scaling performed by spe- cialty contractors is to supplement Caltrans’s own maintenance forces in emergency response situations. On programmed, capital expense projects, scaling plan sheets show exclusion zones, where scaling is not permitted, on oblique photos. Topographic information is provided on these plan sheets when possible. The exclusionary zones display where scaling is not permitted, and may include overhangs that are deemed unsafe to scale beneath or areas that are outside the project limits. Geotechnical experts are on slope during scaling activities. For removal of scaling debris, Caltrans generally pays on a lump-sum basis. Like other states, Caltrans generally relies on expert judgment for estimating the debris quantities according to slope area and characteristics, such as rock quality and joint spacing. Actual volumes are normally within ±20% of the estimate. Safety scaling—scaling requested by the contractor that is not within the permitted scaling area—either is refused because it is within the exclusion zone, or is paid at the contract rate if further review and documentation by Caltrans personnel leads to the enlargement of the permitted scaling area. The addition of the requested area follows a documentation process and is not added “on the fly” during construction activities. This process has avoided excessive additional scaling efforts and excessive expenditures. Colorado Department of Transportation Administration of Scaling The Colorado Department of Transportation (CDOT) has been developing and using a robust geohazards program since 1992, starting with the Colorado Rockfall Accidents on State Highways (CRASH) program and employing a modified Rockfall Hazard Rating System (RHRS), originally created by the Oregon Department of Transportation (Pierson, 1991; Pierson and Van Vickle, 1993; Stover, 1992). Initially focusing on rockfall concerns, CDOT has since 2013 incorporated additional geohazards into its Geohazard Asset Management Program, including rockfall, rockslides, landslides, sinkholes, embankments, debris flows, and erosion issues caused by flooding or severe storm events. Through this program, CDOT has pro- grammed approximately 50% of its scaling activities through STIP or HSIP programs, typi- cally complementing other rockfall mitigation measures. Within this management program, rockfall sites “compete” for mitigation measures with other geohazard sites according to the risk posed to the department and to highway users. Risk factors include safety (including crashes/injuries), mobility, and maintenance costs (e.g., rock downsizing following an event, catchment ditch cleaning, and repair of highway damage caused by rockfall). Geohazards are first graded on an individual site or segment basis, then grouped into corridors graded with “A” through “F” letter grades according to dollar-based risk exposure. Performance targets have been adopted to achieve a grade “B” at 85% of sites statewide. This effectively sets corridors below “B” as eligible for further study and action.

28 Estimating and Contracting Rock Slope Scaling Adjacent to Highways The remaining scaling work is subdivided into emergency response (30%) or routine mainte- nance (15%), or is performed as part of other highway preservation work (5%). To perform scaling work, specialty contractors must pass two qualification hurdles. The first is to become an eligible bidder by exhibiting documentation of bonding and insurance. The second step is achieved with the submittal of the bid packages with documentation of required experience, including 6 months of experience for each scaler, a minimum of 3 years of expe- rience for the scaling supervisor, and corporate experience consisting of completion of three similar projects in the last 3 years. (Note that scalers are permitted to attend a training course conducted by a scaling supervisor in lieu of the 6-month training requirement.) Design Efforts for Scaling CDOT uses “individual scaler hour” as a pay item. This requires the designers to estimate the number of hours it should take for a skilled specialty contractor to scale the slope to an uncertain standard and “as directed by the Engineer.” CDOT’s experience is that a slope’s geologic characteristics (rock quality, joint spacing, lithology, etc.) prevents adherence to a set range of production rates. Potential disputes have been avoided by use of experienced design engineers and geologists and by being able to screen out unqualified, inexperienced contrac- tors through the prequalification process. Where excessively slow production has occurred, it has been attributable to the use of scaling personnel with little experience, working slowly and possibly nervously while suspended from ropes. Despite having no set production rate, CDOT estimates that 10 work days is a reasonable scaling duration for a slope 100 feet high and 500 to 700 feet long for a crew of three qualified scalers. Scaling Plans and Specifications In CDOT’s experience, having geotechnical personnel on site to direct and oversee scaling operations and utilization of the prequalification process has prevented other potential issues when the scaling specifications handle uncertainty with “as directed by the engineer” language. They have rarely encountered disputes regarding estimated hours, and when the engineer’s estimate is surpassed, it is frequently due to the site conditions being worse than what was visible on the slope surface. In these circumstances, actual durations exceed estimates generally no more than 25%. For safety scaling, CDOT considers this incidental to the required scaling. This has normally not been problematic, as the scaling is most often specified on a cut face rather than on the natural slopes above. When natural slopes have posed risks, CDOT design personnel have included targeted scaling on these slopes as part of the contract efforts. Safety spotters have also been a solution to provide an early warning should rockfall occur. Payment for removal of scaling debris is measured using one of two options, either unit volume removed or time and materials used. CDOT’s selection of which method will be applied is determined by the ultimate destination of the debris; if CDOT specifies disposal location for eventual reuse of select materials, such as setting aside large boulders for stream bank armoring, time and materials used is the preferred payment method. In other cases, it is measured by unit volume, as determined by truck counts or volumetric survey. Estimation of design quantities is performed using expert judgment. When required, CDOT typically specifies contractor-designed roadway or rockfall protec- tion measures. The contractor’s design is required to meet performance criteria contained in the specifications, and failure of the system is the contractor’s financial responsibility. When

Case Examples 29 the feature being protected is of high value or particularly sensitive, the contractor must submit the proposed design for CDOT review and concurrence. This submittal review takes place after contract award. In some projects, a CDOT-owned moveable rockfall barrier is an option for the contractor to consider. Scaled Slope Performance and Lessons Learned CDOT encourages its maintenance personnel to use its rockfall activity reporting system to record and document the occurrence of rockfall. While the process isn’t uniformly and univer- sally implemented, CDOT has observed two trends based on the slope’s characteristics. If the rock is poor quality, with close joint spacing, they have observed increases in short-term rockfall activity followed by long-term improvement. Where the rock is higher quality, with wider joint spacing, short- and long-term improvements are realized immediately. CDOT has one of the longer-running statewide programs for managing rockfall. Slope scaling has been a regular part of its rockfall mitigation toolbox for decades. One of CDOT’s primary lessons learned from this experience has been the invaluable nature of having an owner’s rep- resentative with extensive rock slope experience on site directing scaling efforts and making the determination of when scaling is complete. Idaho Transportation Department, District 6 Administration of Scaling Projects and Construction Activities The six districts of the Idaho Transportation Department (ITD) operate semi-autonomously with regard to scaling practice. District 6, covering eastern Idaho’s mountainous terrain north and northeast of the Snake River Plain toward Yellowstone National Park, has established a unique and successful scaling program. The program is led by the district’s engineering geologist. Sites to be scaled are decided upon through the combined use of a rockfall activity database maintained by ITD and the Idaho State Police, spreadsheets with RHRS ratings and rankings of select corridors, and rock slopes where scaling and draped steel mesh would provide significant improvements. Sites that would be only partially mitigated with scaling and draped mesh are recorded for later, more complex rockfall mitigation efforts. By actively avoiding slopes that require more in-depth mitigation measures, ITD expects that it will eventually need to change or adjust this program to account for more complex geology and more difficult conditions. Budgeting is set at $100,000 annually for this district and includes both scaling activities and draped mesh installation. This sum includes outsourced labor for scaling and traffic control. Materials, such as draped mesh materials, anchor materials, and grout; traffic control devices; and internal ITD costs are not included in this amount. Annual activities cease when the budget is exhausted. Often, projects are picked up again the following season until they are completed. The scaling is accomplished with the use of a private specialty scaling contractor with support from ITD’s maintenance and geotechnical personnel. The contractor scales loose rock and installs draped mesh at the direction of the engineering geologist. ITD maintenance personnel haul debris away, stockpiling useful rock for future use (bank armoring, shoulder improve- ments, and gabion basket fill) and placing waste materials in exhausted or unused material sources as part of their reclamation plans. Maintenance also provides all traffic control devices, while the scaling contractor provides traffic control labor. As part of directing duties, ITD’s geologist helps with acquiring and transporting construction materials. On average, the scaling crew can complete approximately 8,000 to 10,000 square feet of slope scaling per week.

30 Estimating and Contracting Rock Slope Scaling Adjacent to Highways Scaled Slope Performance and Lessons Learned ITD District 6 has learned that executing and maintaining an annual scaling program pro- vides a number of benefits. These benefits include being able to address slopes that may have experienced an uptick of rockfall activity in the late winter or early spring months that can then be scaled that same year. This avoids costly emergency response programs and the time- consuming environmental permitting and PS&E (plans, specifications, and engineer’s estimate) process, provided work activity is accomplished within ITD’s right-of-way and can be addressed solely by scaling or draped mesh. ITD has compared this partially insourced program with fully outsourced programs. In the same area and similar geologic conditions, ITD has incurred costs of $260,000 for a fully out- sourced program at one rockfall site. This compares with $105,000 for two slopes and twice the total treatment area for those projects completed within the partially insourced program. Note that this comparison is not detailed for the mitigation measures and quantities used at each slope, but does illustrate the value that ITD District 6’s maintenance scaling program provides to the department. Through the close working relationship that the district engineering geologist has with the scaling contractor, a non-adversarial and balanced rapport is achieved. This fosters a sense of trust between the owner and contractor and results in improved project outcomes. The success of this program is evidenced by slopes that were once some of the most active, problematic rockfall sites becoming some of the least active following scaling and draped mesh installation. New Hampshire Department of Transportation Administration of Scaling New Hampshire performs roughly 90% of its scaling work as part of other highway preserva- tion or improvement projects, a significantly higher proportion than that of other states. More than a decade of conscientious relationship building between the New Hampshire Department of Transportation’s (NHDOT) highway design and geotechnical groups has enabled the depart- ment to adopt a quasi-proactive approach to scaling slopes. The geotechnical group maintains a statewide rock slope inventory, and the highway design group routinely calls during the planning stage to ask if scaling work should be added to a slope within the project limits. In approximately 90% of cases, scaling is added to the project during this stage, though scaling limits and efforts may be constrained by right-of-way or environmental concerns. Because scaling is routinely incorporated into highway preservation projects, scalers are almost always subcontractors to the general contractor, with qualification requirements set by the state. In cases where both scaling and rock bolting are required, NHDOT requires that both tasks be performed by the same contractor. This is in response to previous difficulties where a rock bolt contractor wished to perform additional safety scaling on a slope scaled by a separate contractor. Design Efforts for Scaling In estimating production rates for a scaling project, NHDOT draws on institutional knowl- edge. The state’s typical rock slopes are composed of crystalline rock with wide joint spacing, and production rates have been relatively predictable. A review of roughly a dozen recent proj- ects showed production rates ranging from 750 to 1,500 square feet of rock slope face per scaler per day, with a maximum production rate of 2,333 square feet per scaler per day. NHDOT reports that for these slopes, a significant source of variation in production rates is slope height,

Case Examples 31 which impacts how often scalers have to rope up. Production rates and scaled volumes on slopes with significant differential erosion features are more difficult to estimate, but are less common in New Hampshire. Almost all scaling design work is performed in-house by NHDOT, with only a small propor- tion designed by consultants. During construction, an observer from the geotechnical group is on site at least 90% of the time. This helps address any issues as they arise, while providing support for the regular construction inspector, who may have limited experience observing scaling work. Plans and Specifications for Scaling Scalers hired by the general contractor must meet the specifications developed by NHDOT. Because the state provides full-time inspection and observation services during construction, NHDOT is able to limit the level of detail regarding scaling extent in the specifications. Hand scaling and machine scaling are paid at separate rates, but the specifications make clear that hand scaling includes all tools, such as air pillows and boulder busters, that may be required to scale individual large blocks. Scaling is paid for by the individual scaler hour. NHDOT has used crew hours in the past, but the difficulty of maintaining a constant crew size throughout the project made this logistically challenging from an accounting perspective. Instead, the department provides an estimate of the crew size that will be required for the project, but pays according to the hourly work performed by each individual member of that crew. The general contractor is also responsible for disposing of excavated scaling material and designing adequate traffic protection measures. Partly because of the relatively small size of the scaling work in comparison with the overall contract, disposing of scaling waste has not been an issue for contractors. Traffic protection must meet the approval of NHDOT. The design goal is 100% retention during construction. This is typically achieved by cleaning out the ditch, taking a lane, and installing jersey barriers on the centerline. Temporary closures or traffic stops may also be used, depending on the functional requirements of the roadway. For rare situations where additional rockfall protection has been required, such as a moveable rockfall barrier, the state has paid the contractor an additional amount to develop a temporary system that met project needs. Slope Scaling Performance and Lessons Learned NHDOT has a database of RHRS-type ratings for rock slopes, and scaled slopes are re-rated for entry in the database. Rockfall activity is largely monitored on an ad-hoc basis, with main- tenance personnel calling in to report specific rockfalls. Events that maintenance perceives as “routine” are likely underreported in this system. Anecdotally, NHDOT, as with some other scaling states, notes a temporary increase in the number of small rocks falling from a slope immediately after scaling is completed, which then rapidly tapers off. Like many agencies, NHDOT is working to integrate advanced techniques in rock slope management. The state has recently received a STIP grant to collect photogrammetrically derived point clouds of rock slopes and analyze them using change detection programs. Photo acquisition has been from UAVs or ground-based equipment. The second round of point cloud image collection is currently under way. Implementation of this program will allow the depart- ment to better assess rockfall activity on both scaled and unscaled slopes. It also helps identify unstable blocks earlier in the design process on the basis of observed slope deformation. Finally,

32 Estimating and Contracting Rock Slope Scaling Adjacent to Highways by routinely tracking rock slopes, NHDOT will have the ability to more accurately incorporate rockfall risks into project selection tools. Earlier incorporation of scaling into project design will make it easier for the department to identify the most cost-effective method for rockfall risk reduction. Ohio Department of Transportation Administration of Scaling In 2007, the Ohio Department of Transportation (ODOT) initiated an RHRS-type rockfall management program under the guidance of Dr. Abdul Shakoor at Kent State University and with software developed by the University of Akron. This original assessment system is currently being transitioned to an Esri Collector app for increased ease of use in the field. At this time, there are approximately 6,000 rock slopes in the database. For the majority of these slopes, rockfall is caused by differential erosion. Twenty-five years ago, all scaling work was emergency response work. Since then, the depart- ment has made a conscious effort to adopt a proactive management approach, with the result being that roughly 60% of all scaling work is now programmed. Rockfall-related work competes with other geotechnical issues, such as landslides and aban- doned mines, for limited mitigation dollars. Scaling projects are selected using a combination of factors. The department then identifies those that appear to be most critical, and contracts three to four of those sites annually for scaling work. These jobs typically require 80 crew hours of scaling work by a three-man crew, but have required up to 230 crew hours. Contractors who bid on these projects hire scalers who meet the qualification guidelines set by the department: 2 years of scaling experience for both scalers and foremen, and 1 year of experi- ence for personnel using mechanical scaling. There is no provision for on-the-job training. Design Efforts for Scaling Design work incorporates information from maintenance, a roadside visual review, and lidar. In cases where specific areas of concern are obscured, inspections may be conducted from ropes or lifts. A total excavation quantity is developed from the available data and is used to guide bid development. Additional safety scaling is typically minor, and is paid at the contract rate. From experience, the department defines average scaling production as 200 square feet per crew hour in its specifications. This assumes a crew of three qualified scalers. When scaling rates are significantly slower than anticipated, a geotechnical professional is brought in to help develop a solution to the poor production rates. In general, four to five department geotechnical personnel are available during the construction process, so construction observation may be conducted by an engineer with limited scaling experience. Plans and Specifications for Scaling Installation of rock bolts and draped mesh require approval by a professional engineer. Pure scaling work is designed and approved in-house, with scaling extents marked on oblique photo- graphs of the slope. Safety measures during scaling work are designed and implemented by the contractor. Items to be protected range from roadway components to trees on state forest reserve land. Temporary road closures are also regularly employed during rockfall mitigation work.

Case Examples 33 ODOT conducts lidar scans of the project area before and after scaling work is conducted to improve their estimates for future projects. Recently, ODOT has acquired UAV technology that has subsequently been used to perform initial inspections following a rockfall event. During the actual project, removal of scaling debris is typically tracked using truck counts, and paid for by the 10-yard-truck unit. Lidar scans, rather than hours, have also been used as the basis of payment on a small number of mechanical scaling projects. Scaled Slope Performance and Lessons Learned The existing rock slope inventory and rating program has enabled ODOT to track improve- ments in slope performance following scaling work. In roughly 75% of cases, scaling improves the slope by one tier—for example, from a tier 4 (high risk of rockfall reaching the roadway) to a tier 3 (moderate risk). Records of rockfall activity are also kept informally. ODOT has struggled with the lack of local scaling crews. Most scaling work is performed by companies from the coastal states, and the distances involved in mobilization can create cost-per-hour irregularities. As a result, prime contractors are motivated to employ mechanical scaling or solutions using earthwork equipment to the extent possible. The lack of local scaling contractors has also hampered the ability of the department to complete projects at their desired rate, as high bids or no bids on a project are a frequent occurrence. Frequently, the solution to this problem is to recut the slope to a shallower, more stable angle, which removes the need for scaling, subsequent installation of draped mesh, or other rockfall mitigation components. ODOT reports that as re-excavating slopes has become more common, the use of draped mesh has decreased statewide, but scaling expenditures have remained steady. Tennessee Department of Transportation Administration of Scaling At the time of writing, the majority of the scaling work of the Tennessee Department of Transportation (TNDOT) (roughly 70%) is performed on an emergency basis following rock- fall events. However, the department, under the direction of the chief engineer, is pushing to transition from a reactive to a proactive approach. In 2007, TNDOT initiated a rockfall management program for department slope assets. As of spring 2019, approximately 1,800 slopes had been inventoried in this system, using RHRS-type ratings. Of these slopes, 30% (roughly 500) had been re-rated, enabling the department to begin collecting data on long-term asset performance and deterioration. Incorporating data from the rockfall management program, mitigation projects were in the development phase for 20 slopes, with the first project bid in summer 2019. TNDOT currently budgets $20 million annually for rockfall-related work. At the time of this writing, approximately 20% of TNDOT’s scaling work is programmed as part of larger rockfall mitigation projects, with an additional 5% of scaling work performed as routine maintenance. TNDOT plans to increase these per- centages in the coming years. Design Efforts for Scaling TNDOT design efforts begin with input from maintenance on slope activity, followed by a visual review of the slope from the roadside by department or consulting geotechnical design personnel. However, the department is currently developing a rope access training program that would enable department personnel to more closely inspect the slope during the initial design phase.

34 Estimating and Contracting Rock Slope Scaling Adjacent to Highways The department has special provisions in the bid package for scaling, specifying minimum experience requirements in terms of years of experience. A prequalified scaler list is also under development by the department, but is not yet readily available to prime contractors. TNDOT reports that since the incorporation of these special provisions, “self-performance”—where general contractors perform work without qualification requirements—has largely vanished, though emergency response work occasionally slips through. Plans and Specifications for Scaling When estimating project costs, the department currently bids scaling by the square yard of rock face to be scaled, but is planning to transition to a time-unit rate of measurement (hours), as this appears to be the more common system of measurement employed by other DOTs. TNDOT has also been an early adopter of using lidar tools to measure volume of scaling debris. By flying a lidar-equipped drone before and after scaling, the department is able to quickly and accurately assess the total volume removed by the contractor. Where this measure- ment method is not used, ditch cleanup and removal of scaling debris are both measured by weight, with trucks being weighed at highway scales. During construction, an inspector reviews work from the ground as part of other inspection duties. If possible, the engineer in charge will call and request a site visit from a geotechnical specialist for the final post-scaling inspection. In emergency response situations, final inspec- tions are typically conducted from the ground because of the scheduling constraints asso- ciated with emergency work. Programmed slopes are more likely to receive a close inspection post scaling. Scaled Slope Performance and Lessons Learned By shifting rockfall management from a reactive to a proactive approach, TNDOT reports it has been able to access additional federal funding. At the time the RHRS inventory was under- taken, programmed department rockfall expenditures were limited to roughly $2 million annually in ditch cleaning. Once more information was available for a proactive asset manage- ment approach, the annual maintenance budget was increased to $10 million, and later $20 million following federal matching. The RHRS program also provides a framework for cataloguing rockfall activity and for tracking post-scaling slope performance. This database enables TNDOT to improve their risk assessments over time and to calculate the return on investment obtained from scaling work.

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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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