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Highway Rock Cut Inventory and Failure Potential, Allegany County, Maryland

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Highway Rock Cut Inventory and Failure Potential, Allegany County, Maryland SPR-Part B MD-20-P01837 G-1 MARYLAND DEPARTMENT OF TRANPORTATION STATE HIGHWAY ADMINISTRATION RESEARCH REPORT Highway Rock Cut Inventory and Failure Potential, Allegany County, Maryland David K. Brezinski Rebecca Kavage Adams Elizabeth R. Sylvia Maryland Geological Survey Maryland Department of Natural Resources FINAL REPORT May 2020 This material is based upon work supported by the Federal Highway Administration under the State Planning and Research program. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the Federal Highway Administration or the Maryland Department of Transportation. This report does not constitute a standard, specification, or regulation. TECHNICAL REPORT DOCUMENTATION PAGE 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. MD-20-P01873G-1 4. Title and Subtitle 5. Report Date May 11, 2020 Highway Rock Cut Inventory and Failure Potential, 6. Performing Organization Code Allegany County, Maryland 7. Author(s) 8. Performing Organization Report No. David K. Brezinski, Ph.D., Rebecca Kavage Adams, Elizabeth Sylvia DNR 12-041720-227 9. Performing Organization Name and Address 10. Work Unit No. Maryland Geological Survey 2300 St. Paul Street 11. Contract or Grant No. Baltimore, Maryland 21218 SP809B4F 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Maryland Department of Transportation (SPR) SPR-B Final Report State Highway Administration (May 14, 2018-May 11, 2020) Office of Policy & Research 707 North Calvert Street Baltimore MD 21202 14. Sponsoring Agency Code (7120) STMD - MDOT/SHA 15. Supplementary Notes 16. Abstract One hundred ninety-five, MDOT SHA-maintained, roadway embankments in Allegany County, Maryland, were cataloged as to the effects of climate, vegetation, and geology factors on slope stability. Observations included dimensions, weathering condition, and geologic structure. Recorded data was employed to evaluated the potential for slope failure such as rockfall, rock roll, rockslide, or slumping. Rockfalls were determined to be likely on slopes of greater than 60 degrees, and in massive lithologies on embankments displaying major levels of differential erosion. Rock roll was the most common potential slope failure on slopes that exceed 30 degrees of inclination. Rockslides were considered to be the dominant potential slope failure in outcrops where rock layering is inclined towards the highway. Roadside slumping or rotational dislocations were a prominent type of slope failure in highly weathered, relatively unconsolidated, rock outcrops. 17. Key Words 18. Distribution Statement Rockfalls, Translational landslides, Rockslides, This document is available from the Research Rotational landslides, Roadway embankments. Division upon request. 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price None None 36 pages Form DOT F 1700.7 (8-72) Reproduction of completed page authorized Department of Natural Resources Resource Assessment Service MARYLAND GEOLOGICAL SURVEY Richard A. Ortt, Jr., Director HIGHWAY ROCKCUT INVENTORY AND SLOPE FAILURE POTENTIAL, ALLEGANY COUNTY, MARYLAND by David K. Brezinski Rebecca Kavage Adams Elizabeth R. Sylvia DNR Publication No. DNR 12-041720-227 May 2020 Table of Contents Page Acknowledgements ..................................................................................................................................... 1 Executive Summary .................................................................................................................................... 2 Introduction ................................................................................................................................................. 2 Purpose ................................................................................................................................................. 3 Location and Physiography .................................................................................................................. 3 Bedrock Geology .................................................................................................................................. 5 Previous Study ...................................................................................................................................... 7 Roadway Embankment Failure Survey ....................................................................................................... 7 Methods ................................................................................................................................................ 7 Survey123 ............................................................................................................................................. 9 General Survey Elements ..................................................................................................................... 9 Slope Information .......................................................................................................................... 9 Benches and Catchment ................................................................................................................. 9 Climate ......................................................................................................................................... 10 Water on Exposure ....................................................................................................................... 13 Slope Vegetation .......................................................................................................................... 14 Type of Hazard ............................................................................................................................ 16 Geology Survey Elements ................................................................................................................. 16 Failure Plane Character ................................................................................................................ 16 Rock Friction ............................................................................................................................... 17 Differential Erosion ..................................................................................................................... 18 Weathering Characteristics .......................................................................................................... 19 Stratification ................................................................................................................................. 20 Lithology ...................................................................................................................................... 21 Site Specific Outcrop Survey Utilizing Areal Drone Imagery ........................................................... 24 Methods ....................................................................................................................................... 24 Advantages ................................................................................................................................... 24 Disadvantages .............................................................................................................................. 24 Analysis ....................................................................................................................................... 26 Evaluation of Survey Geology Elements ........................................................................................... 27 Geology Factors Summary ................................................................................................................. 32 Glossary .................................................................................................................................................... 33 References ................................................................................................................................................. 34 List of Figures Figure 1. LiDAR location Map ................................................................................................................... 4 Figure 2. Bedrock stratigraphy and Structure of Allegany County, Maryland ........................................... 5 Figure 3. ESRI Survey123 data collection form ......................................................................................... 8 Figure 4. Embankment Characterization .................................................................................................. 10 Figure 5 Benches and Catchments ............................................................................................................ 11 Figure 6. Maryland Precipitation and Freeze/Thaw Durations ................................................................ 12 Figure 7. Water from Exposure................................................................................................................. 13 Figure 8. North-South-Facing Vegetation ................................................................................................ 14 Figure 9. Types of Vegetation .................................................................................................................. 15 Figure 10. Type of Slope Failure .............................................................................................................
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