National Academies Press: OpenBook

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

Chapter: Chapter 5 - Conclusions and Research Opportunities

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Suggested Citation:"Chapter 5 - Conclusions and Research Opportunities." 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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Page 36
Suggested Citation:"Chapter 5 - Conclusions and Research Opportunities." 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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Page 36
Page 37
Suggested Citation:"Chapter 5 - Conclusions and Research Opportunities." 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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Page 37

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35 Conclusions According to input from 42 departments of transportation and two regional divisions of the Office of Federal Lands Highway, scaling loose rock from highway rock slopes is an important aspect of improving rock slope safety in mountainous areas. Ongoing weathering and deteriora- tion of rock slopes in an aging transportation network will require a gradual increase in rockfall mitigation work, of which scaling is a significant first step. Responses indicated that many of the methods that form the themes and major points of earlier literature, such as scaling from the top downward, requiring scalers with documented experience, and employing a time basis for pay items, have been used by most scaling states. Many other items, such as details on estimating productivity, how to contract and pay for debris removal, best practices for plan preparation, and how temporary protection is designed and contracted, have not been adequately documented. The following are the key findings of this synthesis. Reliance on Expert Judgment A predominant theme is a reliance on experience, which recognizes unique aspects of access- ing and working on rock slopes high above the highway. The experience of both scaling per- sonnel and designers matters to the success of a scaling project. For scaling, experience, and judgment play a greater role than in other highway construction projects because of the absence of engineered quantity measurements (such as bridge deck area), predictable and routine perfor- mance measures (e.g., 30-day concrete compressive strength), and clear completion milestones (e.g., bridge opening). Most scaling states reported that they had obtained satisfactory scaler judgment through the use of experience requirements defined in construction contract docu- ments, though some standard guidelines may help those DOTs with infrequent scaling projects to achieve better outcomes. Designer experience has often been accounted for by maintaining in-house expertise or through established processes for professional services acquisition, such as qualification-based procurement methods. Department-run scaling programs, such as that run by Caltrans, have maintained experience levels for both scaler and designer through exten- sive and well-documented training regimens. Overall, successful scaling projects can be realized when all professionals involved have demonstrable experience, recognize and acknowledge the uncertainties inherent in slope scaling, and work toward the common goal of efficiently and safely mitigating rockfall hazards. Selecting Slopes to Scale Transportation departments often have hundreds or thousands of rock slopes adjacent to their highway systems. Many of these slopes could benefit from periodic rock slope scaling. C H A P T E R 5 Conclusions and Research Opportunities

36 Estimating and Contracting Rock Slope Scaling Adjacent to Highways If a 15-year interval between scaling efforts, the longest interval that was encountered in the literature search for this synthesis, were implemented on all of a hypothetical state’s 1,000 rock slopes, 67 scaling projects per year would be required to achieve full coverage—a significant project count that no state appears to achieve. Therefore, DOTs are selecting which slopes to scale and which ones not to scale. They typically follow one of four approaches: (1) emergency response, where a slope fails and then needs to be scaled to restore safety; (2) programmatic approaches, sometimes facilitated by rockfall or geohazard management programs, and well- recorded rockfall maintenance records informing geotechnical personnel where rockfall hazards exist; (3) maintenance programs, where DOT personnel select slopes to be scaled; or (4) scaling slopes during other highway projects when non-rockfall-related work is planned. Proactive selection could prevent rockfall-related road closures and injuries, though this study found a wide range of selection methods noted and little industry guidance. Some DOTs and federal agencies have recently been adopting or developing geotechnical asset management programs to provide enhanced decision support tools for reducing rockfall and other geohazard occurrences. Practice Varies in Preparing Plans and Specifications Scaling plans that clearly communicate scaling limits and heavy or intensive scaling areas with the use of annotated aerial oblique images in the plan set body have been found to be effective by those who use such scaling plans, though they were not in use in most departments. Use of UAVs and other emerging methodologies may assist with the development of these more effective plan sets. Some scaling states were using or planned to begin using these technologies. Specifications that clearly define scaler or corporate experience requirements have helped departments contract with experienced scalers rather than with the lowest bidder, regardless of qualifications. The lack of available local scalers has forced some departments to change or eliminate scaling areas in an effort to reduce rockfall hazards. Scaling is frequently measured and paid for by the hour; a detailed definition of when scaling starts and stops in the specification has led to improved project outcomes. Practice varies for payment of safety scaling on adjoining slopes, but a general consensus is that if the scaling is for an agreed-to safety concern, it is generally a paid effort. Payment for removal of scaling debris varies, but is a paid effort—not incidental—for the majority of scaling projects. Temporary protection measures for scaling have varied significantly, with many departments implementing contractor-designed approaches while others have been dissatisfied with such an approach. A minority typically provided the contractor with detailed temporary protection designs in the plans and specifications package. A variety of temporary protection measures have been used with varying success, though the most common was standard concrete barriers, and the most successful was moveable rockfall barriers. Scaling Activities During Construction Inspection during scaling activities followed a variety of methods that ranged from inexperi- enced personnel periodically inspecting from the ground to experienced geologists and engineers inspecting from ropes full time. Similarly, personnel who accepted that scaling was complete included those with and without experience, either from the ground or on the slope. Given the reliance on experience for many aspects of scaling, the use of inspectors without experience marks a departure at a critical phase of any scaling project.

Conclusions and Research Opportunities 37 Future Research Opportunities The following research opportunities are suggested to address knowledge gaps identified by the synthesis. Scaling Estimation The reliance on experienced personnel in lieu of recorded data to accurately estimate pro- duction leaves departments at risk of losing institutional knowledge as the workforce ages and retires. Some efforts to begin indexing scaling production numbers (scaler productivity, volume estimation, etc.) to rock quality metrics had begun with one department, Caltrans. A wide geographic reach and scaling measurements representative of the common design- bid-build approach to scaling contracting may be applicable to more DOTs than Caltrans’s nationally unique state employee maintenance approach. Research results would assist DOTs with scaling cost estimation and would preserve and document institutional knowledge. Scaling Framework and Best Practices Preparation of a scaling practice framework following research on effective practices would help guide less experienced DOTs with rock slope scaling. Research would focus on areas where risk to the owner, designer, or contractor may be reduced, and where weaknesses inherent with inconsistent or poorly documented practices could be overcome. Design worksheets, sample specifications, and plan sheet examples that incorporate effective practices would be a high- value deliverable from this research. Scaling Decision Support Tools Decision support tools to help departments with selecting which slopes are eligible for scaling and subsequent prioritization criteria may benefit many DOTs. Methods to Manage and Document Poor Production or Poor Performance Some agencies have had to manage contractors with unsatisfactory production rates or other- wise poor performance. Some communicated that a lack of documented performance measures and production rates left them with little justification for terminating contracts or for seeking out additional contractors. Published methods for describing and measuring appropriate and suitable production rates may benefit those DOTs with limited scaling experience. Scaling Database Establishing a national scaling database with values for production rates, rock quality, and slope rating values, among other items, could provide a robust knowledge base for analysis and guidance to help scaling states refine their scaling practices and help less experienced DOTs achieve better project outcomes when scaling is required.

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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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