Cost-Effective and Sustainable Road Slope Stabilization and Erosion Control (2012)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2012 www.TRB.org NAT IONAL COOPERAT IVE H IGHWAY RESEARCH PROGRAM NCHRP SYNTHESIS 430 Research Sponsored by the American Association of State Highway and Transportation Officials in Cooperation with the Federal Highway Administration SubScriber categorieS Environment • Highways • Maintenance and Preservation Cost-Effective and Sustainable Road Slope Stabilization and Erosion Control A Synthesis of Highway Practice conSultantS LAURA FAY MICHELLE AKIN and XIANMING SHI Western Transportation Institute Montana State University Bozeman, Montana

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administra- tors and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in coop- eration with their state universities and others. However, the accelerat- ing growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Asso- ciation and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board of the National Research Coun- cil was requested by the Association to administer the research pro- gram because of the Board’s recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communication and cooperation with federal, state, and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objec- tivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. The needs for highway research are many, and the National Coop- erative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs. NOTE: The Transportation Research Board of the National Acad- emies, the National Research Council, the Federal Highway Adminis- tration, the American Association of State Highway and Transporta- tion Officials, and the individual states participating in the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of this report. NCHRP SYNTHESIS 430 Project 20-05 (Topic 42-09) ISSN 0547-5570 ISBN 978-0-309-22362-1 Library of Congress Control No. 2012934386 © 2012 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their manuscripts and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to repro- duce material in this publication for classroom and not-for-profit pur- poses. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMSCA, FTA, or Transit development Corporation endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any development or reproduced material. For other uses of the material, request permission from CRP. NOTICE The project that is the subject of this report was a part of the National Cooperative Highway Research Program conducted by the Transpor- tation Research Board with the approval of the Governing Board of the National Research Council. Such approval reflects the Governing Board’s judgment that the program concerned is of national importance and appropriate with respect to both the purposes and resources of the National Research Council. The members of the technical committee selected to monitor this project and to review this report were chosen for recognized scholarly competence and with due consideration for the balance of disciplines appropriate to the project. The opinions and conclusions expressed or implied are those of the research agency that performed the research, and, while they have been accepted as appropriate by the technical com- mittee, they are not necessarily those of the Transportation Research Board, the National Research Council, the American Association of State Highway and Transportation Officials, or the Federal Highway Administration of the U.S. Department of Transportation. Each report is reviewed and accepted for publication by the technical committee according to procedures established and monitored by the Transportation Research Board Executive Committee and the Govern- ing Board of the National Research Council. Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from: Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: http://www.national-academies.org/trb/bookstore Printed in the United States of America

THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Charles M. Vest is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the ser- vices of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Acad- emy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is one of six major divisions of the National Research Council. The mission of the Transportation Research Board is to provide leadership in transportation innovation and prog- ress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Board’s varied activities annually engage about 7,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. www.TRB.org www.national-academies.org

NCHRP COMMITTEE FOR PROJECT 20–05 CHAIR CATHERINE NELSON Oregon DOT MEMBERS KATHLEEN S. AMES Michael Baker, Jr., Inc. STUART D. ANDERSON Texas A&M University BRIAN A. BLANCHARD Florida DOT CYNTHIA J. BURBANK PB Americas LISA FREESE Scott County (MN) Community Services Division MALCOLM T. KERLEY Virginia DOT RICHARD D. LAND California DOT JOHN M. MASON JR. Auburn University ROGER C. OLSON Minnesota DOT ROBERT L. SACK New York State DOT FRANCINE SHAW-WHITSON Federal Highway Administration LARRY VELASQUEZ JAVEL Engineering, Inc. FHWA LIAISONS JACK JERNIGAN MARY LYNN TISCHER TRB LIAISON STEPHEN F. MAHER COOPERATIVE RESEARCH PROGRAMS STAFF CHRISTOPHER W. JENKS, Director, Cooperative Research Programs CRAWFORD F. JENCKS, Deputy Director, Cooperative Research Programs NANDA SRINIVASAN, Senior Program Officer EILEEN P. DELANEY, Director of Publications SYNTHESIS STUDIES STAFF STEPHEN R. GODWIN, Director for Studies and Special Programs JON M. WILLIAMS, Program Director, IDEA and Synthesis Studies JO ALLEN GAUSE, Senior Program Officer GAIL R. STABA, Senior Program Officer DONNA L. VLASAK, Senior Program Officer TANYA M. ZWAHLEN, Consultant DON TIPPMAN, Senior Editor CHERYL KEITH, Senior Program Assistant DEMISHA WILLIAMS, Senior Program Assistant DEBBIE IRVIN, Program Associate TOPIC PANEL ROBERT A. DOUGLAS, Golder Associates, Inc., Mississauga, Ontario ASIF FAIZ, World Bank (retired) ANTHONY R. GIANCOLA, Washington, DC G.P. JAYAPRAKASH, Transportation Research Board MICHAEL T. LONG, Oregon Department of Transportation DAVID P. ORR, Cornell University PATRICIA A. CAZENAS, Federal Highway Administration, (Liaison) BEN RIVERS, Federal Highway Administration, Atlanta (Liaison) GORDON KELLER, Taylorsville, CA (Liaison) Cover figure: A road shoulder shallow slope stabilization project using the “deep patch” treatment with several layers of Geogrid rein- forcement. A joint project of the U.S. Forest Service and the Plumas County, California, Road Department (courtesy: G. Keller). ACKNOWLEDGMENTS This report would not have been possible without the help of Gail Staba, and the input and guidance from project panel members. We would like to thank everyone who responded to our survey as well as those who participated in follow-up interviews and provided photo- graphs, including Tiffany Allen, Vickie Bender, Chris Bennett, Pete Bolander, Jianje Chen, Xueping Chen, Paul Clark, Jeff Currey, Dr. Donald Gray, Jim Haang, Stuart Jennings, Byron Johnson, Kathy Kinsella, Chris Marr, Khalid Mohamed, David Orr, Dave Polster, Skip Ragsdale, Steve Romero, Warren Schlatter, Roger Skirrow, Robbin Sotir, David Steinfeld, Bob Vitale, and Stan Vitton. We would also like to thank the staff at the Western Transportation Institute for support on this project, specifically Andy Scott.

Highway administrators, engineers, and researchers often face problems for which infor- mation already exists, either in documented form or as undocumented experience and prac- tice. This information may be fragmented, scattered, and unevaluated. As a consequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or alleviat- ing the problem. There is information on nearly every subject of concern to highway administrators and engineers. Much of it derives from research or from the work of practitioners faced with problems in their day-to-day work. To provide a systematic means for assembling and evaluating such useful information and to make it available to the entire highway commu- nity, the American Association of State Highway and Transportation Officials—through the mechanism of the National Cooperative Highway Research Program—authorized the Transportation Research Board to undertake a continuing study. This study, NCHRP Proj- ect 20–5, “Synthesis of Information Related to Highway Problems,” searches out and syn- thesizes useful knowledge from all available sources and prepares concise, documented reports on specific topics. Reports from this endeavor constitute an NCHRP report series, Synthesis of Highway Practice. This synthesis series reports on current knowledge and practice, in a compact format, without the detailed directions usually found in handbooks or design manuals. Each report in the series provides a compendium of the best knowledge available on those measures found to be the most successful in resolving specific problems. In the United States it is estimated that 75% of all roads are low-volume roads maintained by some 35,000 local agencies. Low-volume roads often omit surface slope protection, and this can lead to slope failure, erosion, and maintenance, safety, and ecological issues. This report presents information on cost-effective and sustainable road slope stabilization techniques, with a focus on shallow or near-surface slope stabilization and related erosion control methods used on low-volume roads. To fully address this, topic planning and site investigation are discussed, as well as erosion control techniques, soil bioengineering and biotechnical techniques, mechanical stabilization, and earthwork techniques. Information presented in this report was obtained through an extensive literature review, and from survey and interview responses. From the survey responses, 30 individuals were interviewed based on the information they made available in the survey. A total of 25 inter- views were conducted over the phone, and in two cases written responses were received. Laura Fay, Michelle Akin, and Xianming Shi, Western Transportation Institute, Mon- tana State University, Bozeman, Montana, collected and synthesized the information and wrote the report. The members of the topic panel are acknowledged on the preceding page. This synthesis is an immediately useful document that records the practices that were acceptable within the limitations of the knowledge available at the time of its preparation. As progress in research and practice continues, new knowledge will be added to that now at hand. FOREWORD PREFACE By Gail R. Staba, Senior Program Officer, Transportation Research Board

CONTENTS 1 SUMMARY 3 CHAPTER ONE INTRODUCTION What Is Road Slope Stabilization?, 3 What Causes Instabilities?, 4 How Are Road Slopes Stabilized?, 4 How Is a Treatment Determined to Be Cost-Effective or Sustainable?, 5 Methods, 6 8 CHAPTER TWO THE BASICS Planning and Site Investigation, 8 Soil Types and Soil Mechanics, 9 Water Management, 12 Drainage Measures, 12 19 CHAPTER THREE EROSION CONTROL TECHNIQUES Types of Erosion, 19 Grass Seeding, 20 Mulch and Compost, 22 Erosion-Control Geotextiles, 23 Check Dams, 25 Wattles or Fiber Rolls, 27 Straw Bale Barriers, 27 Silt Fences, 28 Chemical Soil Stabilizers, 28 30 CHAPTER FOUR SOIL BIOENGINEERING AND BIOTECHNICAL TECHNIQUES Planning for Soil Bioengineering, 30 Live Stakes, 32 Live Fascines, 33 Brush Layering and Palisades, 33 Branch Packing, 34 Rock Joint Planting, 35 Live and Timber Crib Walls, 36 Vegetated Rock Gabions, 37 Vegetated Rock Walls, 39 41 CHAPTER FIVE MECHANICAL STABILIZATION TECHNIQUES Retaining Walls, 41 Mechanically Stabilized Earth/Geosynthetic Reinforced Soil Systems, 43 In-Situ Soil Reinforcement, 46 49 CHAPTER SIX EARTHWORK TECHNIQUES Implementing Earthwork Techniques, 49 Benched Slopes, 49 Soil Roughening, 51 Extreme Roughening, 51

Flattening Slopes, 52 Landforming, Geomorphic Modification, 52 54 CHAPTER SEVEN CONCLUSIONS AND KNOWLEDGE GAPS Conclusions, 54 Knowledge Gaps, 56 58 REFERENCES 65 APPENDIX A SURVEY QUESTIONS 68 APPENDIX B INTERVIEW QUESTIONS AND RESPONDENTS 70 APPENDIX C SLOPE RATIO VERSUS PERCENT SLOPE DIAGRAM Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at www.trb.org) retains the color versions.