Potential Liability Associated with Unstable Slope Management Programs (2020) / Chapter Skim
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4 NCHRP LRD 82 projects, State DOTs cannot avoid liability for failure to perform routine maintenance of highway slopes.
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NCHRP LRD 82 5 ranked based on a benefit-cost analysis of the proposed remedial construction project.25 Beginning in 1984, the Oregon DOT began planning development of the RHRS, modeled largely on Wyllie's research, in order to better account for rockfall potential, rather than just rockfall history, of all rockfall sites.26 For purposes of RHRS development, a rockfall site was considered to be "any uninterrupted slope along a highway where the level and occurring mode of rockfall are the same."27 Two slope failure modes were considered: (1) where rockfall occurs along natural structural discontinuities (such as joints or bedding planes)
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6 NCHRP LRD 82 considered, the USMS originally required each slope to be evaluated in 19 categories, for which each slope would be assigned a numeric score on a linear scale ranging from 1 (low hazard) to 10 (high hazard)
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NCHRP LRD 82 7 the recommendation of FHWA, and often with funding from FHWA.59 All unstable slope management programs derive to some extent from the rating system proposed by Wyllie and tend to be variations on the Oregon DOT RHRS, the Washington State DOT USMS, or the New York State DOT rock slope rating procedure. In conjunction with this study, the survey questionnaire contained in Appendix B was sent to the 50 State DOTs, typically to the office responsible for statewide asset management.
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8 NCHRP LRD 82 Quality (e.g., friction coefficient) o Differential erosion features and rates • Presence and condition of mitigation measures (e.g., rock bolts, screens)
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NCHRP LRD 82 9 The preliminary rating is heavily driven by local maintenance evaluations of slope failure potential and history.76 The preliminary ratings do not rely on significant data-gathering aside from questionnaires to be completed at the local maintenance level.77 Preliminary ratings can thus be very subjective. Ideally, the local maintenance rating is corroborated or supplemented by centralized State DOT personnel specially trained for the unstable slope management program, who would make observational visits to all sites that have been identified by local maintenance personnel as having significant potential hazard.78 This helps eliminate local bias and ensure consistency in preliminary ratings across the state.
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10 NCHRP LRD 82 some form of benefit-cost decision-making support to better prioritize remediation projects.86 For a given slope, there may be a range of options that can be undertaken to mitigate the risk associated with slope failure, i.e., to reduce the likelihood of personal injury or property damage due to failure.87 Duncan Wyllie's research in the 1990s and beyond has focused on determining the relative influence of the various data categories in contributing to rockfalls, and also the relative effectiveness of various rockfall mitigation measures.88 The following mitigation measures are listed in order of generally increasing cost and effectiveness: • Periodic inspections • Continual monitoring (e.g., instrumentation) • Warning signs or speed limit reductions • Routine maintenance (e.g., cleaning out catchment ditch)
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NCHRP LRD 82 11 which can be calculated from individual data that are included in the USMS and used to calculate the USMS hazard score.93 As in the RHRS method, the "cost" or denominator of the USMS benefit-cost ratio is the cost of the remediation project. Recognizing the inherent limitation that the least expensive (and likely least effective)
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12 NCHRP LRD 82 2. Evolution into Geotechnical Asset Management Programs In the 2012 transportation appropriations bill known as the Moving Ahead for Progress in the 21st Century Act (MAP-21)
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