Montana Department of Transportation October 2017 RESEARCH PROGRAMS Project Summary Report: FHWA/MT-17-008/8239-001 Authors: Darren Beckstrand, C.E.G1 Benjamin George, P.E.1 Brent Black, C.E.G.1 Paul Thompson, Consultant Aine Mines, R.G.1 David Stanley, L.E.G.2 Technology - Portland, OR1 DA Stanley Consulting - Bellingham, WA 2

Rockfall Hazard Process Assessment http://www.mdt.mt.gov/research/projects/geotech/rockfall.shtml

Introduction project scope includes identifying 2 with 29 site visits throughout rock slope condition and risk Montana that were constructed The Montana Department of factors, determining critical since the initial RHRS, had received Transportation (MDT) implemented sites, incorporating benefit/cost mitigation work, or had changed its Rockfall Hazard Rating System analysis, and forecasting future significantly since the 2004 RHRS (RHRS) between 2003 and 2005, asset condition based on various ratings. MDT’s existing RHRS obtaining information on the state’s budget scenarios. The objectives of assessment was supplemented with rock slopes and their associated the program are to 1) update rock four new rating approaches to these hazards. The RHRS data facilitated slope rating criteria; 2) determine sites, but the individual detailed decision-making in an informal critical sites based on condition, rating categories were not changed. process over the next several years. risk, and cost/benefits using new Comparison of results explored MDT applied the RHRS ratings in decision support tools; 3) develop/ different means of evaluating asset an informal process, reviewing cost benefit scenarios; and 4) change, measured as a percent ratings and comparing them to evaluate compatibility of the RAMP change in each method between event occurrences, maintenance process with MDT’s Transportation the 2004 and 2015 ratings. Risk needs, and rockfall mitigation Asset Management program. analyses focusing on mobility and project selection in the decade Landslide Technology of Portland, safety impacts were incorporated since completion. MDT found the Oregon, with team members Paul as part of initial work on decision RHRS to be a valuable tool providing Thompson, DA Stanley Consulting, support tools. relative rankings between sites. and Geographic Communications After nearly a decade of using RHRS, Systems, completed the project in For Task 3, the team developed a MDT decided to develop a more 2017. roadmap for creating performance comprehensive and updated Rock measures for the RAMP that Slope Asset Management Program will help MDT meet its goals (RAMP), beginning in 2015, due What We Did for this geotechnical asset class to a combination of changed and integrate RAMP with MDT’s sites, a need for additional tools The research team applied a multi- transportation asset management to aid in project selection, and a stage approach to update and (TAM) program in the future. desire to incorporate principles of assess MDT’s existing rock slope The team developed different Transportation Asset Management management system in order to performance classes based on (TAM) in managing rock slopes. promote a more efficient use of roadway functional classification, The goal of the new research resources. In addition to the final and proposed minimum standards project is to assess changes in Research Report, separate reports for asset performance. As part of MDT’s rock slope assets since were produced for each of the this work, Landslide Technology 2003 and gather data that would seven sub-tasks, all of which are (LT) used rockfall activity survey allow MDT to develop an updated available online at the above URL. responses from District 1 to develop rock slope hazard assessment risk assessment tools by correlating program with TAM-compatibility Following a literature review in Task rock slope condition with the as an added benefit. The research 1, the project commenced Task likelihood of a -closing rockfall event.

FHWA/MT-17-008/8239-001 1 After adding the new rating approaches and risk assessment tools to a revised rating spreadsheet, a second round of rock slope assessments was conducted in Task 4. Instead of re-rating all rated 869 slopes in the 2004 database, LT worked with MDT to select a smaller group. The final list of 362 slopes included all sites on the Interstate system, both those previously rated and those ‘B’ sites that did not receive a detailed rating in 2004. It also included all ‘A’ sites on segments with an AADT greater than 2,000 vehicles per day. The 2016 field work added 126 previously unrated sites along the Interstate routes to the RAMP database. Figure 1: High-risk corridor segments.

In Task 5, the team worked with MDT asset condition with a per square foot In the Task 6 work, the research team first to select critical sites for conceptual improvement cost. conducted an expert elicitation meeting mitigation cost work. Application with MDT personnel to gather observed of proposed ‘Minimum Acceptable What We Found and perceived deterioration rates of Conditions’ generated a list of 40 MDT’s rock slopes. From these rates, the RAMP sites that did not meet any of As part of the research project, the team team developed an initial deterioration the proposed minimum conditions. In developed cost and risk parameters for model, and used it to perform analyses addition, the event likelihood estimates rock slopes that correlated with asset resulting in decision-support tools, developed for each rock slope as part of condition, as described in the Task 5 and including: Task 3 work were combined with one- 6 reports. Annual likelihood of both • life-cycle cost model, mile roadway segments provided by MDT. service disruptions and accidents were • return on investment model, and Again applying difference performance developed using survey responses from • tradeoff analysis process. targets based on different District 1. An average mitigation unit cost All of which can be used to support roadway functional classifications, the was developed by combining the 2004 MDT’s long-term planning and budgeting research team identified 149 one-mile and the 2016 conceptual mitigation work. in support of asset and performance segments in Montana’s transportation Maintenance costs in dollars per square management processes. network where the likelihood of road foot for rock slopes were estimated closing events was greater than the by reviewing annual costs for the two Applying these initial analyses via conceptual risk targets (Figure 1). maintenance job codes (obtained from accepted asset management models, the Combining these one-mile segments MDT) most likely to contain rockfall- researchers examined various funding and site-specific minimum acceptable related work. Maintenance section scenarios and how they would affect conditions, eleven high-risk corridors managers were surveyed on the average network-wide rock slope conditions were identified as potential investment percentage of those codes actually over the next 10 years. The researchers candidates. MDT selected four of these spent maintaining rock slopes, and this concluded that annual funding levels of corridors (Table 1 and Figure 1), which was correlated with the percentage of approximately $28 million will maintain allowed field personnel to visit 75 sites rock slope-adjacent road miles in their current conditions, as indicated by the and develop site-specific conceptual sections. Combining this data with rock yellow highlighted area on Figure 2. mitigation costs. By also updating slope condition in each maintenance The researchers also concluded that if and incorporating the 100 conceptual section enabled development of MDT continues its current method of mitigation cost estimates from the 2004 estimated maintenance costs based on funding rock slope management on a RHRS work, the research team created a asset condition. The various parameters worst-first basis, the modeling indicates mitigation cost dataset that correlated are summarized in Table 2. approximately $35 million per year would be required to maintain current Table 1: Rockfall Mitigation Corridors Identified for Site-Specific Cost Estimates. conditions. These results suggest that No. sites below minimum Approximate 30 yr. risk MDT can save $7 million per year by Location acceptable conditions exposure (millions) taking a proactive approach to prevent Lookout Pass, West of St. Regis, I-90, MP 0-31 0 $17.7 excessive slope deterioration. Gallatin Canyon, Hwy 191, MP 50-63 3 $7.3 Further, the research team conducted Rocky Canyon, East of Bozeman, I-90, MP 315 1 $2.4 an analysis of return on preservation East of West Glacier, US 12, MP 154-158.5 5 $2.3 investment. This showed that MDT can

FHWA/MT-17-008/8239-001 2 Table 2: Rockfall Mitigation Corridors Identified for Site-Specific Cost Estimates. research team Annual Risk of Annual Risk of Accident Average Cost per ft2 to 2 2 recommends that MDT Condition/State Disruption per ft Rock Face per ft Rock Face Mitigate to Good Condition take the following 1/Good 1.19E-08 5.94E-09 -- steps: 2/Fair 4.76E-08 2.38E-08 $8.20 • Move forward 3/Fair 3.91E-07 1.96E-07 $16.40 to incorporate the 4/Poor 1.26E-06 6.31E-07 $24.60 RAMP into MDT’s 4/Poor 2.02E-06 1.01E-06 $32.80 TAM Plan as soon as practicable. In the recoup every dollar spent on preserving assets into its 2015 TAM Plan is to develop interim, continue rock slopes and also realize a benefit of an a Geotechnical Asset Management Plan development of RAMP processes additional $1.14 for every dollar spent. that is compatible with or part of MDT’s and data collection in methods TAM Plan. compatible with MDT’s asset By monetizing the safety risks referenced management and performance in Table 2, the researchers also developed In summary, we found the principal management processes. an incremental benefit/cost equation bottom-line conclusion of the research • Integrate condition and risk that is particularly useful when choosing is that if MDT continues its current assessments into budget allocation how to best allocate funds with a given practices, maintaining rock slopes in and department planning so rock corridor or district on an annual basis, current condition will cost $35 million slopes are considered as elements and applied it to the Task 5 conceptual per year. If the tools developed in this of projects early in the planning mitigation sites as an example of how research are used to support decision- process or as stand-alone projects it could be used to choose sites from making based on life-cycle costs and other as warranted by risk, slope condition the group as a whole, or from within a considerations, maintaining rock slopes in and other considerations. particular target corridor. current condition will cost an estimated • Develop a continuing STIP project $28 million per year – a savings of $7 for maintaining and improving the In Task 7, the research team evaluated million per year for the same outcome. RAMP and for rock slope preservation the compatibility of the new RAMP with Taking advantage of the savings requires projects. MDT’s existing TAM program. The team continued development of the decision- • Utilize the Condition State approach concluded that MDT’s well-developed making tools, monitoring condition and for developing rock slope design TAM Plan, P3 Performance Programming costs of rock slopes and integration of the goals. Process and TranPlan21 provide the RAMP into or at least compatible with, • Update site data after mitigation/ guidance needed for developing and MDT’s TAM Plan. repair work or construction of new incorporation of the RAMP rock slope slopes. management process. In addition, What the Researchers • Track rockfall events and rock slope while federal law and guidance primarily Recommend specific maintenance costs, ideally as focuses on and pavement they occur assets, the law supports and encourages • Maintain licenses for online In order to maintain the quality of the inclusion of other assets in TAM plans, database to support collecting and current rock slope database, and ensure including geotechnical assets such as storing rock slope data and enable that it continues to provide useful rock slopes. The path toward MDT communication of rock slope information to the Department, the incorporation of rock slopes and other condition and cost. • Conduct another large-scale site assessment in 5 years, consistent with other asset management standard of practice. These recommendations, if undertaken, will help MDT improve the preliminary correlations, costs, and models developed in this research project at regular intervals. This will make the decision support tools more useful and budget-related planning more accurate, increasing Department benefit from the RAMP.

Figure 2: Network-Level RAMP Slope Condition Index versus Funding.

FHWA/MT-17-008/8239-001 3 For More Details . . .

The research is documented in Report FHWA/MT-17-008/8239-001, http://www.mdt. mt.gov/research/projects/geotech/rockfall.shtml.

MDT Project Manager: Sue Sillick, [email protected], 406.444.7693

Researcher’s Organization Project Manager: Darren Beckstrand, [email protected], 503.452.1200

To obtain copies of this report, contact MDT Research Programs, 2701 Prospect , PO Box 201001, Helena MT 59620-1001, [email protected], 406.444.6338.

MDT Implementation Status: October 2017

Eight implementation recommendations were made to MDT. These recommendations, along with MDT’s response, are documented in the implementation report, which can be found at the above URL.

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