Alaska Department of Transportation & Public Facilities Research & Technology Transfer Documenting Best Management Practices for Cutslopes in Ice‐rich Permafrost Prepared by: Ted S. Vinson, Ph.D., P.E. Robert L. McHattie, P.E. Date May 2009 Prepared for: Alaska Department of Transportation Statewide Research Office 3132 Channel Drive Juneau, AK 99801‐7898 Publication Number FHWA‐AK‐RD‐09‐01 Foreword Ice-rich permafrost is often encountered during the construction of roads and other projects in Alaska. Ice-rich permafrost is typically silt with segregated ice or massive ground ice. During the thawing process there are trafficability and stability problems due to thawing of fine grained, ice-rich soils. Also, resource agencies are increasingly critical of by-products of the thawing process – particulate-rich effluent and terrain disfigurement. Alaskan transportation engineers must employ one of two methods to deal with ice-rich permafrost encountered during construction. The decision may be to preserve the ice-rich soil in its frozen state. Preservation is possible given enough time and money. However, it is often much too expensive to preserve the frozen state of materials especially in areas of relatively warm permafrost. The alternate approach, which is addressed in this report, is to characterize and accommodate the thawing process using a design method that minimizes the negative effects of thawing. More specifically, it is necessary to control the thawing process so that the materials remain structurally stable and to make sure that the products of the process (e.g., particulate laden runoff) are disposed of in an environmentally acceptable manner. A primary focus of this report is the problem of ice-rich cuts. The report also discusses disposal of ice-rich excavation materials and the formation of embankments using ice-rich fill. The techniques employed or proposed to mitigate the problems are described and several best management practices are presented in Appendix B. This is a final research report (1st printing). The research was funded by the FHWA with the intention of supporting Alaskan Department of Transportation and Public Facilities (ADOT&PF) geotechnical and construction engineers who must routinely confront permafrost. It is also recommended reading for all engineering consultants involved in such work. Notice This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document. 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Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestion for reducing this burden to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-1833), Washington, DC 20503 1. AGENCY USE ONLY (LEAVE BLANK) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED FHWA-AK-RD-09-01 May 2009 Final 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS Documenting Best Management Practices for Cutslopes in Ice-rich Permafrost DOT &PF AKSAS #76987 HPR-4000(60)/ T2-07-04 6. AUTHOR(S) Ted S. Vinson, Ph.D., P.E. Robert L. McHattie, P.E. 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT Ted S. Vinson, Ph.D., P.E. NUMBER 33070 Peoria Road Corvallis, Oregon 97333 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING AGENCY State of Alaska, Alaska Dept. of Transportation and Public Facilities REPORT NUMBER Research, Development and Technology Transfer 2301 Peger Rd FHWA-AK-RD-09-01 Fairbanks, AK 99709-5399 11. SUPPLENMENTARY NOTES Performed in cooperation with the U.S. Department of Transportation, Federal Highway Administration. 12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161 (http://www.ntis.gov) 13. ABSTRACT (Maximum 200 words) In northern Alaska ice-rich permafrost is often encountered during the construction of roads and other projects. When ice-rich permafrost is exposed during late spring through early fall the potential for thawing is great. Ice-rich permafrost, typically silts with segregated ice or massive ground ice, experiences a substantial reduction in strength owing to the exceedingly high water content and lack of drainage and consolidation during thaw. The result can be a quagmire that “bogs down” equipment or, if the exposure is a cutslope, slope failure. In addition to trafficability and stability problems, environmental oversight increasingly focuses attention on particulate-rich effluent and poor aesthetics which are common by-products of the thaw process. This study presents several construction projects in northern Alaska where problems due to thawing permafrost were a significant environmental concern. The techniques employed or proposed to mitigate the problems are described and several best management practices are presented. 15. NUMBER OF PAGES 14- KEYWORDS : 66 construction; environment; excavation; ice-rich permafrost; management; thawing 16. PRICE CODE N/A 17. SECURITY CLASSIFICATION OF 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT REPORT OF THIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified N/A SI* (MODERN METRIC) CONVERSION FACTORS APPROXIMATE CONVERSIONS TO SI UNITS Symbol When You Know Multiply By To Find Symbol LENGTH in inches 25.4 millimeters mm ft feet 0.305 meters m yd yards 0.914 meters m mi miles 1.61 kilometers km AREA in2 square inches 645.2 square millimeters mm2 ft2 square feet 0.093 square meters m2 yd2 square yard 0.836 square meters m2 ac acres 0.405 hectares ha mi2 square miles 2.59 square kilometers km2 VOLUME fl oz fluid ounces 29.57 milliliters mL gal gallons 3.785 liters L ft3 cubic feet 0.028 cubic meters m3 yd3 cubic yards 0.765 cubic meters m3 NOTE: volumes greater than 1000 L shall be shown in m3 MASS oz ounces 28.35 grams g lb pounds 0.454 kilograms kg T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t") TEMPERATURE (exact degrees) oF Fahrenheit 5 (F-32)/9 Celsius oC or (F-32)/1.8 ILLUMINATION fc foot-candles 10.76 lux lx fl foot-Lamberts 3.426 candela/m2 cd/m2 FORCE and PRESSURE or STRESS lbf poundforce 4.45 newtons N lbf/in2 poundforce per square inch 6.89 kilopascals kPa APPROXIMATE CONVERSIONS FROM SI UNITS Symbol When You Know Multiply By To Find Symbol LENGTH mm millimeters 0.039 inches in m meters 3.28 feet ft m meters 1.09 yards yd km kilometers 0.621 miles mi AREA mm2 square millimeters 0.0016 square inches in2 m2 square meters 10.764 square feet ft2 m2 square meters 1.195 square yards yd2 ha hectares 2.47 acres ac km2 square kilometers 0.386 square miles mi2 VOLUME mL milliliters 0.034 fluid ounces fl oz L liters 0.264 gallons gal m3 cubic meters 35.314 cubic feet ft3 m3 cubic meters 1.307 cubic yards yd3 MASS g grams 0.035 ounces oz kg kilograms 2.202 pounds lb Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T TEMPERATURE (exact degrees) oC Celsius 1.8C+32 Fahrenheit oF ILLUMINATION lx lux 0.0929 foot-candles fc cd/m2 candela/m2 0.2919 foot-Lamberts fl FORCE and PRESSURE or STRESS N newtons 0.225 poundforce lbf kPa kilopascals 0.145 poundforce per square inch lbf/in2 *SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. (Revised March 2003) i TABLE OF CONTENTS Page INTRODUCTION 1 EROSION MECHANISMS 2 THERMAL EROSION OF ICE-RICH CUTSLOPES EXPOSED DURING CONSTRUCTION 2 MITIGATION OF THERMAL EROSION OF ICE-RICH CUTSLOPES 4 DISPOSAL OF EXCAVATED PERMAFROST 9 USE OF EXCAVATED PERMAFROST TO BUILD AN EMBANKMENT 10 FIRE AND PERMAFROST 10 SUMMARY AND CONCLUSIONS 11 IMPLEMENTATION 11 APPENDIX A - REGULATORY ENVIRONMENT 12 APPENDIX B - BEST MANAGEMENT PRACTICES 15 ACKNOWLEDGEMENTS 25 REFERENCES 25 ii List of Figures 1. Photo. Road Cut in Ice-Rich Permafrost (from ADOT&PF file) …………………….…..27 2. Photo. Thaw Degradation of Cut Slope in Ice-Rich Permafrost (from ADOT&PF file)....27 3. Photo. Thawed Ice-Rich Permafrost Flowing Around a Bulldozer Blade. (Photo by Pewe, 1954) ...………………………………………………………….…………………..……..28 4. Photo. Dalton Highway Cut in Ice-Rich Permafrost – Before Thaw (from ADOT&PF file courtesy of S. Lamont and J. Russell) ...…………………………………………….……..31 5. Photo. Dalton Highway Cut in Ice-Rich Permafrost – After Thaw (from ADOT&PF file courtesy of S. Lamont and J. Russell) …………………….……………………………….34 6. Original 1969 Engineer’s Sketch of the Procedure to be Employed in a “Special Roadway Section” Defined as Ice Rich or Massive Ice Cutslopes (after Rooney, R & M Consultants, Inc., 2007) ......……………………………………………………………………………..35 7. Near Vertical Cutslopes with a Widened Ditch Section ……………………….………….37 8. Photo. Trees felled(cut) at the Top of a Near Vertical Cutslope in Permafrost.