Unstable Slope Management in GRSM Primary Road Network
Introduction
• Condition assessments for unstable slopes along 151 miles of roadway
- Rockfall (Planar, Wedge, Toppling, Raveling/Undermining, Rock Avalanche, Indeterminate failures, Differential Erosion)
- Landslide (Translational, Rotational, Debris Flows, Shallow Slump, Erosional Failures)
• Web database (USMP.info), Mobile Application Unstable Slope Management Program for Federal Land Management Agencies (USMP for FLMA)
- Searching capabilities https://usmp.info/client/login.php
- Interactive web map with twenty-six independent input parameters
Screenshot of the USMP.info web map
References: Beckstrand et al., 2019; USMP for FLMA, 2017
Unstable Slope Inventory
- Digital geodatabase
- 285 discrete slopes
- 280 rockfall sites
- 5 landslide sites
Preliminary and Total USMP Ratings
Preliminary Rating - Good (15-21 pts) | Fair (22-161 pts) | Poor (>161 pts) Total USMP Rating - Good (<200 pts) | Fair (200-400 pts) | Poor (>400 pts)
Highest Ranked Sites (USMP Total Score)
Gatlinburg Spur Rd (GRSM-0011N, GRSM-0011S)
Highest Ranked Sites (USMP Total Score)
Newfound Gap Rd (GRSM-0010N, GRSM-0010S)
Highest Ranked Sites (USMP Total Score)
Little River Gorge Rd (GRSM-0014) & Laurel Creek Rd (GRSM-0015)
Highest Ranked Sites (USMP Total Score)
Foothills Parkway (GRSM-0008A, GRSM-0008E -- GRSM-0008H)
Recent Rockfalls
February 12, 2021, on the southbound Gatlinburg Spur, closed one lane of traffic. The unstable slope was captured in GRSM_219 (poor rated 554) during field data collection on Nov. 3, 2019.
February 11, 2020, on the northbound Gatlinburg Spur, closed for several hours 500 cubic yards of debris in a 100-foot-long and 70-foot-tall area (WJHL News, 2020). The unstable slope was captured in GRSM_233 (fair rated 386) during field data collection on Dec. 16, 2019.
Recent Rockfalls
February 12, 2021, on the southbound Gatlinburg Spur, closed one lane of traffic. The unstable slope was captured in GRSM_219 (poor rated 554) during field data collection on Nov. 3, 2019.
February 11, 2020, on the northbound Gatlinburg Spur, closed for several hours 500 cubic yards of debris in a 100-foot-long and 70-foot-tall area (WJHL News, 2020). The unstable slope was captured in GRSM_233 (fair rated 386) during field data collection on Dec. 16, 2019.
Rockfall Susceptibility Model
MaxEnt
- Unstable Slope Inventory (280 rockfall hazard)
- Bedrock geology
- Digital Elevation Model
- Fault layer
- Mean temperature coldest quarter (Dec, Jan, Feb)
- Annual precipitation
- 800-meter spatial resolution
Rockfall Risk Estimate
Total USMP Rating (sum of preliminary rating, total hazard rating, and total risk rating) of all unstable slopes using Ordinary Kriging
Final Risk Estimate Map
Co-Kriging with (i) Total USMP Rating and (ii) Rockfall Susceptibility Model
Applications
Site Prioritization
- Kernel Density Estimation (KDE) to identify clusters of poorly rated unstable slopes
- Weighted Overlay Analysis using distance to road, distance to faults, geology ranked by predicted acid-producing potential, slope (degrees), KDE using USMP Risk score, and KDE using USMP Hazard score.
Selected High Rated Slopes
- Fourteen sites selected based on results from the weighted overlay analysis
- Gatlinburg Spur (North): 1 site
- Gatlinburg Spur (South): 2 sites
- Newfound Gap Rd: 3 sites
- Little River Gorge Rd: 4 sites
- Foothills Pkwy Section 8E: 2 sites
- Lakeview Drive East: 2 sites
Acid Base Accounting
Rockfall Simulations
[Add Map in Powerpoint]
Slope Risk Warning Signs
21 existing rockfall hazard warning signs throughout GRSM
The catalog of rockfall warning signs overlaid on rockfall risk map provides an opportunity for GRSM to assess the current placement of signs.
Conclusions
- Unstable Slope Inventory Database for GRSM with USMP Risk Rating
- Unstable Slope Risk Map for visual reference
- Several Applications - byproduct from USMP Risk Rating
- Site Prioritization using effective, and time efficient method
- Rockfall assessment of slopes at risk - can assist in determining remedial measures
- Presence of acid producing rocks along ~20 miles of the primary road network (Anakeesta, Wehutty, and Copper Hill Formations) - might make waste rock disposal difficult
- Rockfall risk warning signage current locations and how the locations compare to the slopes with high risk rating
Future Direction
- Rockfall assessment of all 285 unstable slopes - can assist in determining management effort and remedial measures
- Investigation of all slopes along Anakeesta, Wehutty, and Copper Hill Formations can provide detailed Acid Base Accounting, in turn can help with waste rock management decision making process
- Acid-producing rock was a contributing factor in rockslides on the Blue Ridge Parkway, could the same be true for GRSM?
- Detailed investigation of rockfall risk warning signage that aligns with the mission and goals of GRSM
Acknowledgements
This work was completed as part of a task grant agreement between the National Park Service and the East Tennessee State University Department of Geosciences.
Additional funds were provided by the Mayo Educational Foundation, Inc., the American Federation of Mineralogical Societies, and the East Tennessee State University Department of Geosciences.
We would also like to acknowledge the GRSM maintenance staff for sharing their knowledge of past slope failure events and our undergraduate field assistants for their help performing condition assessments.
