Assessing the Long-Term Performance of Mechanically Stabilized Earth Walls (2012)

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APPENDIX E EXAMPLES OF EXISTING METHODOLOGY AND TOOLS DEVELOPED AND PROVIDED BY AGENCIES

Materials from FHWA’s Wall Inventory Program

Materials from Nebraska Department of Roads

Materials from Ohio Department of Transpportation

Materials from Utah Department of Transportation

Example MSE Wall Evaluation Form (Plan/Drainage View and Cross-Section sheets not shown)

Abbreviations used without definitions in TRB publications: AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation

TRANSPORTATION RESEARCH BOARD 2012 EXECUTIVE COMMITTEE* OFFICERS Chair: Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson Vice Chair: Deborah H. Butler, Executive Vice President, Planning, and CIO, Norfolk Southern Corporation, Norfolk, VA Executive Director: Robert E. Skinner, Jr., Transportation Research Board MEMBERS VICTORIA A. ARROYO, Executive Director, Georgetown Climate Center, and Visiting Professor, Georgetown University Law Center, Washington, DC J. BARRY BARKER, Executive Director, Transit Authority of River City, Louisville, KY WILLIAM A.V. CLARK, Professor of Geography and Professor of Statistics, Department of Geography, University of California, Los Angeles EUGENE A. CONTI, JR., Secretary of Transportation, North Carolina DOT, Raleigh JAMES M. CRITES, Executive Vice President of Operations, Dallas-Fort Worth International Airport, TX PAULA J. C. HAMMOND, Secretary, Washington State DOT, Olympia MICHAEL W. HANCOCK, Secretary, Kentucky Transportation Cabinet, Frankfort CHRIS T. HENDRICKSON, Duquesne Light Professor of Engineering, Carnegie Mellon University, Pittsburgh, PA ADIB K. KANAFANI, Professor of the Graduate School, University of California, Berkeley GARY P. LAGRANGE, President and CEO, Port of New Orleans, LA MICHAEL P. LEWIS, Director, Rhode Island DOT, Providence SUSAN MARTINOVICH, Director, Nevada DOT, Carson City JOAN MCDONALD, Commissioner, New York State DOT, Albany MICHAEL R. MORRIS, Director of Transportation, North Central Texas Council of Governments, Arlington TRACY L. ROSSER, Vice President, Regional General Manager, Wal-Mart Stores, Inc., Mandeville, LA HENRY G. (GERRY) SCHWARTZ, JR., Chairman (retired), Jacobs/Sverdrup Civil, Inc., St. Louis, MO BEVERLY A. SCOTT, General Manager and CEO, Metropolitan Atlanta Rapid Transit Authority, Atlanta, GA DAVID SELTZER, Principal, Mercator Advisors LLC, Philadelphia, PA KUMARES C. SINHA, Olson Distinguished Professor of Civil Engineering, Purdue University, West Lafayette, IN THOMAS K. SOREL, Commissioner, Minnesota DOT, St. Paul DANIEL SPERLING, Professor of Civil Engineering and Environmental Science and Policy; Director, Institute of Transportation Studies; and Acting Director, Energy Efficiency Center, University of California, Davis KIRK T. STEUDLE, Director, Michigan DOT, Lansing DOUGLAS W. STOTLAR, President and CEO, Con-Way, Inc., Ann Arbor, MI C. MICHAEL WALTON, Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin EX OFFICIO MEMBERS REBECCA M. BREWSTER, President and COO, American Transportation Research Institute, Smyrna, GA ANNE S. FERRO, Administrator, Federal Motor Carrier Safety Administration, U.S.DOT LEROY GISHI, Chief, Division of Transportation, Bureau of Indian Affairs, U.S. Department of the Interior, Washington, DC JOHN T. GRAY II, Senior Vice President, Policy and Economics, Association of American Railroads, Washington, DC JOHN C. HORSLEY, Executive Director, American Association of State Highway and Transportation Officials, Washington, DC MICHAEL P. HUERTA, Acting Administrator, Federal Aviation Administration, U.S.DOT DAVID T. MATSUDA, Administrator, Maritime Administration, U.S.DOT MICHAEL P. MELANIPHY, President and CEO, American Public Transportation Association, Washington, DC VICTOR M. MENDEZ, Administrator, Federal Highway Administration, U.S.DOT TARA O’TOOLE, Under Secretary for Science and Technology, U.S. Department of Homeland Security, Washington, DC ROBERT J. PAPP (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, U.S. Department of Homeland Security, Washington, DC CYNTHIA L. QUARTERMAN, Administrator, Pipeline and Hazardous Materials Safety Administration, U.S.DOT PETER M. ROGOFF, Administrator, Federal Transit Administration, U.S.DOT DAVID L. STRICKLAND, Administrator, National Highway Traffic Safety Administration, U.S.DOT JOSEPH C. SZABO, Administrator, Federal Railroad Administration, U.S.DOT POLLY TROTTENBERG, Assistant Secretary for Transportation Policy, U.S.DOT ROBERT L. VAN ANTWERP (Lt. Gen., U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers, Washington, DC BARRY R. WALLERSTEIN, Executive Officer, South Coast Air Quality Management District, Diamond Bar, CA GREGORY D. WINFREE, Acting Administrator, Research and Innovative Technology Administration, U.S.DOT *Membership as of July 2012.

NAT IONAL COOPERAT IVE H IGHWAY RESEARCH PROGRAM NCHRP SYNTHESIS 437 TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2012 www.TRB.org Research Sponsored by the American Association of State Highway and Transportation Officials in Cooperation with the Federal Highway Administration SUBSCRIBER CATEGORIES Bridges and Other Structures • Highways • Maintenance and Preservation • Railroads Assessing the Long-Term Performance of Mechanically Stabilized Earth Walls A Synthesis of Highway Practice CONSULTANT Travis M. Gerber URS Corporation Salt Lake City, Utah

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FOREWORD PREFACE By Jon M. Williams Senior Program Officer Transportation Research Board Mechanically stabilized earth (MSE) walls are retaining walls that rely on internal rein- forcement embedded in the backfill for stability. This study addresses methods currently used to assess long-term performance of MSE walls, where “long-term” denotes the period of time from approximately one year after the wall is in service until the end of its design life. The focus of the study is on state and federal agency wall inventories, including meth- ods of inspection and assessment of wall conditions. Information was gathered through a literature review, agency survey, and selected interviews. Travis M. Gerber, URS Corporation, Salt Lake City, Utah, 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. 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.

CONTENTS 1 SUMMARY 3 CHAPTER ONE INTRODUCTION Background and Objective, 3 Methods of Study, 3 Organization of Report, 4 5 CHAPTER TWO STATE OF MECHANICALLY STABILIZED EARTH WALL INVENTORY PRACTICE Introduction, 5 Parties with Responsible Charge for Mechanically Stabilized Earth Walls, 5 Agencies Having Inventories, 6 Nature and Scope of Inventories, 6 Constraints on Inventory Development and Asset Management Activities, 8 10 CHAPTER THREE COLLECTION OF MECHANICALLY STABILIZED EARTH WALL DATA Types of Data Contained in Wall Inventories/Databases, 10 Frequency of Field Inspections and Monitoring Activities, 16 Collection of Corrosion and Degradation Data, 16 20 CHAPTER FOUR ASSESSMENT AND USE OF MECHANICALLY STABILIZED EARTH WALL DATA Assessment and Interpretation of Data, 20 Use of Performance Assessments in Decision Making, 22 24 CHAPTER FIVE OUTCOMES AND LESSONS LEARNED Policies and Practices Developed to Improve Performance of Mechanically Stabilized Earth Walls, 24 Most Important “Lesson Learned”, 25 27 CHAPTER SIX CONCLUSIONS Current State of Practice, 27 Direction of State of Practice, 27 Effective Practices, 28 Areas Needing Improvement and/or Research, 28 29 REFERENCES 31 APPENDIX A SURVEY QUESTIONNAIRE 43 APPENDIX B LIST OF SURVEY RESPONDENTS

45 APPENDIX C “MOST SIGNFICANT LESSON(S) LEARNED” AS REPORTED BY AGENCIES 47 APPENDIX D RESEARCH PROBLEM STATEMENT 49 APPENDIX E EXAMPLES OF EXISTING METHODOLOGY AND TOOLS DEVELOPED AND PROVIDED BY AGENCIES APPENDIX E IS WEB-ONLY AND CAN BE FOUND AT WWW.TRB.ORG, SEARCH ON “NCHRP SYNTHESIS 437.” 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.

Mechanically stabilized earth (MSE) walls are an important class of infrastructure assets whose long-term performance depends on various factors. As with most all other classes of assets, MSE walls need periodic inspection and assessment of performance. To date, some agencies have established MSE wall monitoring programs, whereas others are looking for guidance, tools, and funding to establish their own monitoring programs. The objective of this synthesis project is to determine how transportation agencies monitor, assess, and predict the long-term performance of MSE walls. The information used to develop this synthesis came from a literature review together with a survey and interviews. Of the 52 U.S. and 12 Canadian targeted survey recipients, 39 and five, respectively, responded. This synthesis reveals that unlike bridges and pavements, MSE walls and retaining walls in general are often overlooked as assets. Fewer than one-quarter of state-level transportation agencies in the United States have developed some type of MSE wall inventory beyond that which may be captured as part of their bridge inventories. Fewer still have the methods and means to populate their inventories with data from ongoing inspections from which assess- ments of wall performance can be made. In the United States, there is no widely used, consistently applied system for managing MSE walls. Wall inventory and monitoring practices vary between agencies. This synthesis examines existing practices concerning the nature, scope, and extent of existing MSE wall inventories. It also examines the collection of MSE wall data, including the types of perfor- mance data collected, how they are maintained in wall inventories and databases, the fre- quency of inventory activities, and assessment practices relevant to reinforcement corrosion and degradation. Later parts of this synthesis discuss how MSE wall performance data are assessed, interpreted, and used in asset management decisions. This synthesis finds that the most well-implemented wall inventory and assessment sys- tem in the United States is the Wall Inventory Program developed by FHWA for the National Park Service. However, this system, like some others, uses “condition narratives” in a process that can be somewhat cumbersome and subjective. Other systems use more direct numeric scales to describe wall conditions, and an advantage of such systems is that they are often compatible with those used in assessments of bridges. As experience with MSE walls accumulates, agencies will likely continue to develop, refine, and better calibrate procedures affecting design, construction, condition assessment, and asset management decisions. One portion of this synthesis is dedicated to summarizing the actions taken thus far by survey respondents to improve the long-term performance of their MSE walls. Many agencies prescribe the use of a pre-approved wall design and/or wall supplier. Other actions or policies frequently focus on drainage-related issues. Also included as part of this synthesis are statements from survey respondents as to what the most important lesson learned by their agency has been. Although the scope of the SUMMARY ASSESSING THE LONG-TERM PERFORMANCE OF MECHANICALLY STABILIZED EARTH WALLS

2 responses is broad, certain topics appear more frequently than others, with the four most fre- quent being (in order of decreasing frequency) drainage, construction, backfill, and modular block issues. In examining various reported practices for inventorying and assessing the performance of MSE walls, those appearing to be more effective are: (1) use of inventory and assessment systems with features that are simple to use and as objective as possible; (2) use of rating cri- teria that are specific to particular wall elements and/or conditions; (3) use of numeric rating scales that correspond to other scales already in use for other asset classes such as bridges; and (4) the incorporation of MSE wall inventory and assessment systems into systems for other asset classes. An important conclusion of this synthesis is that there exists a need for greater recogni- tion of MSE walls (and retaining walls in general) as important infrastructure assets. In the same vein, a greater number of agencies need to be actively involved in MSE wall inventory and assessment activities, and for greatest benefit there should be greater consistency across agencies relative to the way that these activities are performed. The synthesis also finds that performance assessment methodologies need to be more fully developed; similarly, service life prediction and risk assessment methodologies need to be developed. To realize such goals, it appears that greater funding and allocation of other resources is needed. In follow-up discussions regarding the synthesis survey, multiple participants expressed a hope that such increased awareness and resource allocation can be realized without significant, adverse- performance events such as those that led to the legislative creation and ongoing funding of the nation’s bridge inspection and assessment programs.

3CHAPTER ONE INTRODUCTION BACKGROUND AND OBJECTIVE Mechanically stabilized earth (MSE) walls were introduced in the United States about 40 years ago (see Elias et al. 2001). As the technology has improved and gained wider recogni- tion, the number of MSE walls designed and constructed has increased dramatically; however, the long-term performance of these structures depends on various factors, and unfortunately there have been instances of adverse performance. Like every important class of assets, MSE walls need periodic inspection and assessment of performance. To date, some states have established MSE wall monitoring programs, while several others are looking for guidance, tools, and funding to estab- lish their own monitoring programs. This synthesis project is undertaken to determine how state transportation agencies monitor, assess, and predict the long-term performance of MSE walls. This project provides information regarding current methodologies and procedures relating to the following topics: • Inspection and evaluation of the condition of existing MSE walls along the states’ highways; • Maintenance of design and construction information; • Recording and applying the results of inspections in each department’s centralized database; • Monitoring corrosion in MSE walls with inextensible steel reinforcement; • Monitoring degradation of geosynthetics; • Maintenance of internal and external drainage; • Assessment of wall performance and evaluation of the consequences of failure based on these inspection and monitoring programs; • Identification of preservation strategies that can reduce the likelihood of failure of MSE walls; • Assessment of the key causal factors that affect perfor- mance; and • Use of wall data to make programming decisions. It is anticipated that this information will lead to better design, construction, monitoring, and maintenance of these important structures. This project can benefit many state agen- cies by combining the lessons learned from experienced states with the experience and innovative practices of academicians, MSE wall designers, and contractors as presented in technical literature. For the purposes of this synthesis, the following defini- tions are used: • MSE wall: Retaining walls that rely on internal rein- forcement embedded in the backfill for stability. The reinforcement is attached to the wall’s face, which confines the backfill. The reinforcement can be either metallic (strips or meshes) or geosynthetic (fabrics or grids). Soil nail or anchor walls are not considered to be MSE walls for the purposes of this synthesis. • Panel MSE wall: Either one- or two-stage MSE walls that have concrete facing panels; internal soil reinforce- ment is usually metallic. • One-stage MSE wall: A MSE wall that uses a concrete panel attached to the internal reinforcement to retain the backfill. The panel is in direct contact with the backfill. • Two-stage MSE wall: A MSE wall that uses a metal- lic mesh or grid and geosynthetic liner attached to the internal reinforcement to retain the backfill. A concrete panel is subsequently attached to the vertical mesh. The panel is not in direct contact with the retained backfill. This wall type is typically used where settlements are expected to be relatively large. • Block MSE wall: A MSE wall that uses a modular block facing attached to the internal soil reinforcement (which is often geosynthetic), and is often referred to as a segmental block wall. The focus of this synthesis document is the long-term performance of MSE walls, where the term “long-term” nominally refers to the period of time from shortly after con- struction and acceptance of the MSE wall until the end of the design life, which is typically 75 or 100 years. The term “performance” is used in this report to refer to the behavior as well as the functionality and serviceability of a wall. Poor or adverse performance includes any performance that is less than that intended (e.g., serviceability limits are exceeded) and can structurally be manifest as small to large distortions, cracking, and even collapse. METHODS OF STUDY This synthesis project has gathered relevant information through (1) a literature review; (2) a survey of U.S. state and Canadian provincial transportation agencies, as well as other select entities (e.g., FHWA); and (3) interviews with select agencies. The scope of information collected addresses both permanent block and panel types of MSE walls, the latter of which consists of both one- and two-stage varieties. Both

4 extensible and inextensible internal wall reinforcements are also considered. Although the current body of literature contains many descriptions and references to the monitoring and assessment of MSE walls, much of that literature relates to conditions existing during and immediately after construction. For exam- ple, case histories are sometimes presented for particular MSE walls where foundation or geometric conditions are perceived as being particularly adverse or even unique and thus neces- sitating analytical and/or field studies to validate the adequacy of current design or construction processes (e.g., Reddy et al. 2003; Stuedlein et al. 2010). In other instances, MSE wall performance literature is simply the result of the “observa- tion method” (see Peck 1969) being applied and documented for ordinary wall conditions. One also finds case histories and/or forensic assessments of walls that failed (e.g., Bay et al., 2009; Koerner and Koerner 2009; Holtz 2010). Although indirectly related to long-term performance of MSE walls, the literature also contains construction/inspector manuals (e.g., Passe 2000) as well as guidance for the use and deploy- ment of instrumentation for assessing performance during and soon after construction (e.g., Koerner and Koerner 2011). In examining the literature, one also finds academic studies in which walls are monitored throughout the construction process and immediately thereafter (perhaps a year) with the goal of improving design techniques (e.g., Allen and Bathurst 2001). As stated previously, the focus of this synthesis document is the longer-term performance of MSE walls; hence, discussion of this previously referenced portion of literature is minimal. In addition to the literature review, U.S. state and Canadian provincial level transportation agencies were surveyed. The survey questionnaire is presented in Appendix A. The sur- vey was web-based and administered through the Internet. The questionnaire was designed to balance comprehensive- ness with conciseness to maximize benefit while minimiz- ing response effort, which is essential in achieving a high response rate. Thirty-nine of the 52 U.S. and five of the 12 Canadian targeted recipients responded; they are listed in Appendix B. Follow-up interviews with select agencies were undertaken to provide additional details and insights into survey responses. ORGANIZATION OF REPORT This report is organized into six chapters and four appen- dices. Chapter one presents the background and objectives of this synthesis project, explains the methods used, and out- lines the remainder of this document. Drawing on the results of the literature review, survey questionnaire, and select inter- views, chapter two describes the state of MSE wall inven- tory practice with particular emphasis on the nature, scope, and extent of existing inventories. Chapter three discusses the collection of MSE wall data, including the types of performance data collected and maintained in wall inven- tories and databases, the frequency of inventory activities, and aspects relating to reinforcement corrosion and degra- dation. Chapter four reviews how MSE wall performance data are assessed, interpreted, and used in asset management decisions. The chapter also discusses practices of estimating design life and risk assessment for MSE walls. Chapter five presents actions reported by transportation agencies and others to improve the long-term performance of MSE walls. This chapter also presents what survey respondents believe is their greatest lesson concerning long-term performance of MSE walls. Finally, in chapter six, a summary of the key findings of this synthesis project is presented, including the state of practice relative to the long-term performance of MSE walls. Other items presented include the direction of the states of practice, effective practices inferred from the literature review and survey respondents, and areas needing improvement and/or research. The appendices include a copy of the survey questionnaire, a list of survey respondents, and examples of existing methodology and tools developed and provided by agencies (e.g., inspection forms, rating or scor- ing worksheets, and assessment guidelines).

5INTRODUCTION As with bridges and pavements, retaining walls are an essen- tial component of our transportation infrastructure. However, unlike pavement and bridges, retaining walls (of which MSE walls are a growing subclass) are often overlooked as an asset. Proper asset management is essential to making informed, cost-effective program decisions and optimizing existing highway resources. The Roadway Data Highway Performance Management System (HPMS) is a national transportation data system that provides detailed data on highway inven- tory, condition, performance, and operations. It describes functional characteristics, traffic levels, and pavement con- ditions for all interstate highway system sections. In addi- tion to the HPMS, at least 36 individual state departments of transportation (DOTs) collect basic pavement inventory data, while more than 41 DOTs collect some type of data relative to pavement fatigue and cracking as part of their pavement management systems (Cambridge Systematics et al. 2009). With respect to bridges, the federal government has man- dated the creation and maintenance of the National Bridge Inventory (NBI), which contains data on all bridges and cul- verts on or over U.S. roads that are greater than 20 ft long. These bridges are also inspected every two years per the National Bridge Inspection Standards (NBIS). In contrast, there is no dedicated management system addressing the whole of the nation’s retaining walls, MSE or otherwise. Indeed, although asset management guidance is provided for highway features such as pavements, bridges, culverts, guardrails, and drainage structures in the Asset Management Data Collec- tion Guide developed in conjunction with AASHTO (2006), retaining walls are not addressed—despite there being an estimated 16.3 million square meters of various types of walls along the nation’s highways with values ranging from approximately $200 to $2,000 per square meter (DiMaggio 2008). With respect to MSE walls specifically, Berg et al. (2009) indicated that an average of 850,000 square meters of MSE wall with precast facing is built each year in the United States, along with an additional 280,000 square meters of modular block wall. Also, according to Berg et al. (2009), typical total costs for permanent transportation-related MSE walls range from $320 to $650 per square meter of wall face, and modular block walls less than 4.5 m high are less expen- sive by 10% or more. Elias et al. (2004) placed the cost of MSE walls in the somewhat lower range of $160 to $300 per square meter. During the preparation of this synthesis, two documents were found to be of particular interest to users of this syn- thesis, thus meriting specific mention. The first document, Guide to Asset Management of Earth Retaining Structures, by Brutus and Tauber (2009), is the product of a study con- ducted for the AASHTO Standing Committee on Highways, with funding provided through NCHRP Project 20-07. This publication presents methodologies and considerations aimed at helping transportation agencies establish asset manage- ment programs for earth retaining structures (of which MSE walls are a component), with particular focus on the devel- opment of inventories and inspection programs. The pub- lication also presents the results of a survey similar to the one performed for this synthesis regarding the inventory, inspection, and asset management activities of transporta- tion agencies concerning their earth retaining structures. The second document is National Park Service Retaining Wall Inventory Program (WIP)—Procedures Manual, by DeMarco et al. (2010b). This document represents the efforts of the FHWA Office of Federal Lands Highway, working with the National Park Service (NPS), to develop and implement a retaining wall inventory and condition assessment pro- gram [collectively referred to as the Wall Inventory Program (WIP)]. The document describes in detail the data collec- tion and management processes, wall attribute and element definitions, and team member responsibilities for conduct- ing retaining wall inventories and condition assessments as derived from experiences involving nearly 3,500 walls. Although MSE walls constitute only a small fraction of the walls involved in the development of the FHWA’s WIP, much of the material in this document is applicable and/or transferable to matters associated with the long-term per- formance of MSE walls. PARTIES WITH RESPONSIBLE CHARGE FOR MECHANICALLY STABILIZED EARTH WALLS MSE walls are multidisciplinary in nature, having both struc- tural and geotechnical components. Once constructed, main- tenance concerns are introduced. To develop and maintain an effective inventory, some party must first take responsibility CHAPTER TWO STATE OF MECHANICALLY STABILIZED EARTH WALL INVENTORY PRACTICE

6 panel walls, two-stage panel walls, and block walls, respec- tively. The majority of panel walls possess metallic reinforce- ment. Some wall inventories are also maintained by city-level agencies. The cities of Cincinnati, Ohio; New York City, New York; and Seattle, Washington, all maintain retaining wall inventories, including MSE walls. FHWA has developed a wall inventory and database for the National Park Service list- ing more than 3,500 walls, some of which are MSE walls. Although a minority of agencies appear to maintain well- defined MSE wall databases (and fewer still have regular inspections to inform the database beyond the basic identify- ing information), some limited MSE wall inventory and per- formance data are apparently maintained by some agencies. Additionally, some MSE wall inventory and performance data are inherently contained in the NBI and are accessible in software database appli cations such as PONTIS or other agency-maintained databases. These “overlooked” MSE walls would typically be those that serve as bridge abutments or are considered integral to the performance of the bridge structure. These databases contain basic wall information such as spatial dimensions, construction date, and some type of performance rating of bridge support, but greater detail may be lacking. Once recognized, bridge inventory data may be a starting point for developing MSE wall inventories and performance assessments. NATURE AND SCOPE OF INVENTORIES Agencies that have established MSE wall inventories appear to own between 100 and 1,000 MSE walls (with mean and median values of 508 and 400, respectively). However, as explained by Gerber et al. (2008), wall counts can be prob- lematic. Single wall segments at a bridge abutment might be treated as an individual wall, whereas at other times one abut- ment and two adjoining wing-wall segments might be desig- nated as a single wall. Consequently, at a bridge abutment with one MSE wall segment beneath the bridge and two MSE wall segments serving as wing- walls on either side, one could count either one or three walls. If one considers a similar configuration for the other abutment, for the walls. As shown in Table 1, when queried regarding who has responsible charge for MSE walls once the walls are constructed and accepted, 41% of survey respondents noted it was a maintenance engineer at a regional or district level. Those who responded “other” generally indicated a mixed or shared responsibility among the various structural (i.e., “bridge”), geotechnical, and maintenance professionals. Approximately 14% of respondents indicated that no one in their agencies has responsibility for MSE walls after construc- tion and acceptance. AGENCIES HAVING INVENTORIES Several questions of the survey for this synthesis project focused on the nature and extent of transportation agencies’ MSE wall inventories. Thirty (more than two-thirds) of sur- vey respondents indicated that they do not maintain a specific MSE wall inventory. Of the 14 respondents who do have inventories (listed here), 43% reported that the inventory is partial, limited to specific geographic areas, or constrained in some other way. (Although not survey respondents, the states of Ohio, Pennsylvania, and Washington also appear to have at least partial MSE wall inventories. Alberta, Canada, reports “defined problem sites” as a type of wall inventory.) • Alberta, Canada • California • Colorado • Kansas • Minnesota • Missouri • Nebraska • New York • North Carolina • North Dakota • Ontario, Canada • Tennessee • Utah • Wisconsin. In reporting what types of MSE walls are included in their inventories, 100%, 71%, and 86% named one-stage Response Number Percent Structural engineer(s) or similar at an agency-wide level 3 7 Structural engineer(s) or similar at a regional or district level 3 7 Geotechnical engineer or similar at an agency-wide level 3 7 Geotechnical engineer(s) or similar at a regional or district level 0 0 Maintenance engineer or similar at an agency-wide level 4 9 Maintenance engineer(s) or similar at a regional or district level 18 41 No one has this charge 6 14 Other (specify) 7 16 TABLE 1 PARTY HAVING RESPONSIBLE CHARGE FOR MSE WALLS ONCE THE WALLS ARE CONSTRUCTED AND ACCEPTED (most representative response)

7one could assign one, three, or six wall numbers to the MSE wall segments present at a bridge site. (There could be even more than six if additional walls segments were used to support the exterior sides of ramps.) In the literature, there appears to be little consensus regarding methodologies for individual wall designations. However, sev- eral sources suggest that whatever system is used to identify and count walls, physically tagging the walls with identifiers is a helpful practice. Different agencies use different criteria when determining what MSE walls to count and/or include in their inventory/ database. Brutus and Tauber (2009) provide extended dis- cussion of various possible criteria, which commonly include wall height, proximity to the roadway, batter or face slope, wall ownership, structural type, and proximity to bridges or culverts. The main criteria used by FHWA’s WIP are related to jurisdiction (e.g., is the wall along a qualifying road?), proximity of wall relative to roadway, wall height, wall embedment, and wall face angle. [The WIP uses a wall face angle criterion of 45 degrees or greater so that some rockeries and slope protection buttressing are included in the inven- tory, whereas FHWA (see Berg et al. 2009) typically defines a retaining wall as having an internal face angle greater than or equal to 70 degrees to differentiate walls from reinforced slopes.] The FHWA program also advises that when wall acceptance based on the aforementioned criteria is marginal or difficult to discern, “include the wall in the inventory, particularly where the intent is to support and/or protect the roadway or parking area and where failure would sig- nificantly impact the roadway or parking area and/or require replacement with a similar structure.” Based on synthesis survey results shown in Table 2, most inventories include only those walls owned by the agency. Only 57% include walls not associated with a specific bridge or culvert. When a wall height criterion is used, 1.2 or 2 m are the most frequent threshold values. In evaluating the comprehensiveness of inventory data- bases they currently maintain, transportation agencies report that between 10% and 100% (mean and median of 70% and 78%, respectively) of the walls that satisfy their inclusion criteria are accounted for (Table 11 subsequently shows this information by agency). The particular content contained in each respective database varies and is discussed in the next chapter. As mentioned previously, some MSE wall inventory information and performance data are inherently contained in the NBI. These MSE walls would typically be those that serve as bridge abutments or are considered integral to the performance of the bridge structure. Gener- ally, walls that are not within the vertical projection of the bridge deck and are not constructed integrally with either wing-walls or abutments are not included in bridge assess- ment activities. Table 3 summarizes who in an agency principally manages/ maintains its inventory of MSE walls. Most frequently it is a geotechnical engineer or similar person at an agency-wide level. This may be inconsistent as Table 1 indicates that main- tenance engineers at a regional or district level are the individu- als who have responsibility for MSE walls once they are built. It thus appears that there may be a disconnect between those considered responsible for MSE walls and those actually doing the work of asset management. However, such an arrangement need not be problematic; multiple parties can be involved in MSE wall management provided there is a clear understanding that responsibility for the asset may lie in a place other than the location of the data or even the expertise used to collect and/or evaluate the data. Communication and understanding of individual responsibilities would obviously be essential for an effective inventory and assessment program. Inventories can be maintained in various formats and manipulated using various tools. The current state of prac- tice is summarized in Table 4, which lists the variety of Response Number Percent Wall owned by my agency 14 100 Wall owned by others but adjacent to facilities for which my agency is responsible 4 29 Wall owned by others but may negatively impact adjacent facilities for which my agency is responsible 1 7 Wall is associated with a bridge structure 12 86 Wall is associated with a culvert 7 50 Wall is not associated with a bridge or culvert 8 57 Minimum wall height 6 43 Minimum height of retained earth 2 14 Minimum wall length 1 7 Minimum wall area 0 0 Other (specify) 2 14 TABLE 2 CRITERIA USED TO DETERMINE WHAT MSE WALLS TO INCLUDE IN INVENTORY (multiple responses possible)

8 mation regarding maintenance does not appear to be system- atically maintained by any party. CONSTRAINTS ON INVENTORY DEVELOPMENT AND ASSET MANAGEMENT ACTIVITIES During oral interviews with select survey participants, the participants frequently identified the lack of a government/ legislative directive along with the lack of allocated fund- ing as significant impediments either to initially develop- ing their MSE wall inventory or subsequently populating it with performance data from inspection activities. Although some increasing awareness and impetus toward asset man- agement for retaining walls appears to have existed in the early to mid-2000s (partially characterized by the devel- opment and distribution of informational brochure “Earth Retaining Structures and Asset Management,” developed by FHWA (2008), it appears that the economic down- turn of 2008 through the present has largely halted those efforts. In Colorado, for example, a plan for implementing a state-wide monitoring program for all types of retaining walls and sound walls was developed for the state DOT (Hearn 2003). Although the feasibility report concluded that “no impediment [was] found to full development of standard data and procedures for walls and sound barri- ers,” little progress toward implementation has been made as yet because of funding constraints. DOTs in Oregon (see Turner 2008), Nebraska, Ohio, and Utah have simi- methods used to manage MSE wall inventories, with pref- erences given to simple spreadsheets or MS access-type databases. The potential range of information maintained as part of an MSE wall inventory is broad. Data regarding wall location and geometry are perhaps the most common elements, but depend- ing on the use of the inventory/database, other information might be maintained, including wall features, construction data, and inspection information. Brutus and Tauber (2009) suggest that information such as dates of construction and repairs, geo- metric wall dimensions, wall materials including backfill type, specific element types and manufacturers, as-built and shop drawings, specifications, quality control test data, and inspec- tion reports be included. They also suggest that a wall database should include basic traffic-volume data. Hearn (2003) offers similar suggestions. Table 5 summarizes the frequency at which different types of information is collected and/or maintained by surveyed agencies as part of their wall inventories. The most frequently tracked metrics are wall location by route/milepost and wall type. These metrics are followed by date constructed, rein- forcement type, and shop drawings. Given that degradation and/or corrosion of reinforcement is a primary concern of agencies (as revealed in a subsequent section of this report), it is logical that these two particular and apparently coupled metrics are among the more frequently tracked items. Infor- Response Number Percent Structural engineer(s) or similar at an agency-wide level 4 29 Structural engineer(s) or similar at a regional or district level 0 0 Geotechnical engineer or similar at an agency-wide level 5 36 Geotechnical engineer(s) or similar at a regional or district level 0 0 Maintenance engineer or similar at an agency-wide level 0 0 Maintenance engineer(s) or similar at a regional or district level 3 21 Other (specify) 2 14 TABLE 3 PARTY WHO PRINCIPALLY MANAGES/MAINTAINS INVENTORY OF MSE WALLS (most representative response) Response Number Percent File boxes/cabinets 3 21 Spreadsheet 4 29 MS Access database without GIS support 3 21 Oracle database without GIS support 1 7 PONTIS 1 7 Other non-GIS supported database (specify) 2 14 GIS-based software (specify) 0 0 TABLE 4 PRIMARY TOOL USED AS AN ASSET MANAGEMENT SYSTEM FOR MSE WALL INVENTORY (most representative response)

9evaluation and inventory of its MSE walls out of corrosion concerns (Wheeler 2002). In follow-up discussions regarding the synthesis survey, many respondents expressed hope that increased awareness and resource allocation could be achieved before any signifi- cant, adverse events such as those that led to the creation and ongoing support of the nation’s bridge inspection and assess- ment programs. larly reported that initially developed and/or implemented plans could not be sustained. In the mid-1980s, Califor- nia’s DOT (Caltrans) established procedures and responsi- bilities for monitoring, sampling, and testing the MSE wall structures; however, in 1997, budgetary constraints elimi- nated the program. Some MSE wall inspections continue, but the process is not systematic. New York State’s DOT is an exception to this trend; its inventory and assessment efforts date to 1985, when the state began an initial field Response Num ber Percent Location by Street Address 3 2 1 Location by Latitude/Longitude 4 2 9 Location by Route, Milepost 7 5 0 Location by State Plane Coordinates 1 7 Wall Type 6 4 3 Wall Function 3 2 1 Wall Geometrics—Maximum Wall Height 4 29 Wall Geom etrics—Average Wall Height 4 29 Wall Geometrics—Wall Length 4 2 9 Wall Geometrics—Slope in Front of Wall 2 14 Wall Geom etrics—Slope Behind Wall 2 14 Wall Geom etrics—Road/Traffic Offset 3 2 1 Date Constructed 5 3 6 Manufacturer 4 29 Contractor/Installer 1 7 Reinforcem ent Type 5 36 Drainage Conditions—Proximity of External Water Sources 0 0 Drainage Conditions—Location and Condition of Drainage Points 2 14 Nature of Adjacent Facilities Owned by Agency 1 7 Nature of Adjacent Facilities or Utilities Owned by Others (e.g., railroad) 0 0 Characterization of Adjacent Roadway Traffic 2 14 Design Data 1 7 Construction Data—Plans 4 29 Construction Data—Specifications 2 14 Construction Data—Shop Drawings/Submittals 5 36 Construction Data—Inspection Documentation 2 1 4 Construction Data—As-Builts 4 29 Post-construction Modifications 1 7 Photographs 4 2 9 Condition of Structure—External Inspection Data 3 21 Condition of Structure—Internal (e .g., corrosion) Inspection Data 0 0 Maintenance Activities 0 0 Other (specify) 1 7 TABLE 5 TYPES OF DATA AGENCIES GENERALLY COLLECTED OR MAINTAINED FOR MSE WALLS (multiple responses possible)

10 At perhaps its most basic level, effective asset management consists of three components: (1) data collection; (2) data assessment and interpretation; and (3) taking action consis- tent with asset performance goals. Each of these three com- ponents is constrained by available resources. This chapter will focus on the data collection component. TYPES OF DATA CONTAINED IN WALL INVENTORIES/DATABASES Not all data are helpful in meeting asset management goals. Rather, the appropriate data must be collected—data that can be reliably quantified and assessed so that meaningful conclu- sions regarding performance can be drawn. In practice, data collection often focuses on potential symptoms of adverse performance and is obtained during field investigations and inspections. Alzamora and Anderson (2009) provide a review of MSE wall performance issues based on their expe- rience with FHWA. They particularly identified geometry/ wall layout, obstructions, wall embedment, surface drainage, backfill placement and compaction, panel joints, leveling pad, and durability of facing as potential problem areas. Consis- tent with their findings, most data collection efforts currently undertaken relate to the condition and performance of these particular elements. Several agencies have developed guidance manuals and/ or inspection forms for gathering post-construction wall per- formance data. Examples of some of these materials devel- oped by FHWA (DeMarco et al. 2010b), Nebraska (Jensen and Arthur 2009; Nebraska Department of Roads 2009), Ohio (Ohio Department of Transportation 2007), and Utah (Bay et al. 2009) are provided as examples in web-only Appendix E. There are also MSE wall inspection manuals that focus on installation/construction issues (e.g., New York State Department of Transportation 2007), but these usu- ally do not explicitly address long-term wall performance. A feature common to several of the above-cited manu- als is the use of photographs illustrating the nature of a par- ticular feature needing identification (such as a sand cone in front of a wall joint, indicative of backfill migration) and/or quantification of its severity (minor verses major amounts of concrete degradation). The picture and the man- uals themselves serve a calibration purpose when multiple individuals are involved in data collection; without a com- mon baseline, data scatter can be excessive, particularly when the metric is subjectively quantified (i.e., not directly measurable). Perhaps the best documented, large wall inventory pro- gram in the United States is FHWA’s Wall Inventory Pro- gram (WIP). Extensive guidance and discussion concerning data collection methods are presented in the WIP Procedures Manual (DeMarco et al. 2010b). The WIP Procedures Man- ual emphasizes that “collected wall data must be accurate, concise and descriptive.” Photographic documentation dur- ing data collection efforts is also encouraged. For MSE wall types, data collection and rating focuses on the following primary wall elements: wire/geosynthetic facing, concrete panels, manufactured block, wall foundation materials, and wall drains. Applicable secondary wall elements include road/shoulders, upslope, downslope, and lateral slope. Rather than being numeric in nature or measurement-based, the con- dition data collected for each wall element consist of a written “condition narrative,” which is “a concise, descriptive narrative of element condition sufficient to characterize severity, extent, and urgency of element distresses” (DeMarco et al. 2010a). To help ensure consistency, these narratives use terminology and definitions consistent with the types of potential distress described in Figure 1. As seen in this figure, element ratings reflect observa- tional wall condition data relative to four distress categories: corrosion/weathering, cracking/breaking, distortion/deflection, and lost bearing/missing elements. These narratives are later converted to a numerical “condition rating” ranging from 1 to 10 using the descriptions shown in Table 6. This process is sub- jective, and rating variances among inspectors are reported to be within plus-or-minus two rating points for a given element. In the FHWA WIP, a general wall performance rating is also determined along with the element condition ratings. This rating scheme is shown in Table 7. Use of the wall performance rating is illustrated using the following example from the WIP procedures manual (DeMarco et al. 2010b, p. 101): For example, an MSE wall with a geogrid-wrapped face shows little sign of specific element distress (geogrid and backing geo- textile are largely unweathered, drains are working, etc.). How- ever, the wall is differentially settling at one end, as evidenced by a 3- to 6-inch vertical sag extending full-height in the wall face. A tension crack has begun to open at the top of the wall just beyond the estimated length of reinforcements, further indi- cating a global or external wall failure mechanism is actively CHAPTER THREE COLLECTION OF MECHANICALLY STABILIZED EARTH WALL DATA

11 FIGURE 1 Element condition narrative guidance (DeMarco et al. 2010b).

12 developing. The inspecting engineer describes the overall wall performance as ‘low,’ providing appropriate narrative describ- ing the state of global distress, and rates the wall performance at a ‘4’ per the rating definitions. As discussed in the next chapter, these element condition rat- ings combined with the wall performance ratings create an overall wall performance rating ranging from 5 to 100, and these ratings are used in assessment management decisions. Although not quite as detailed as the FHWA WIP just pre- sented, Brutus and Tauber (2009) have also developed a guide to asset management of earth structures. They indicate that con- ditions listed here could be indicative of wall stress or deterio- ration, and recommend that the precise vertical and horizontal locations where these conditions are observed should be docu- mented. Brutus and Tauber also suggest that a severity or prior- ity rating such as (1) low, (2) moderate, (3) high, or (4) urgent be assigned as conditions are assessed in the field. Rating Rating Definition 9 to 10 Excellent No-to-very low extent of very low distress. Defects are mi nor, are within the normal range for newly constructed or fabricated elements, and m ay include those resulting from fabrication or construction. In practice, ratings of 9 to 10 are only given to elem ents with very minor to no distress whatsoever—conditions typically seen only shortly after wall construction or substantial wall repairs. 7 to 8 Good Low-to-moderate extent of low severity di stress. Distress does not significantly compromise the element function, nor is there significant severe distress to major structural components. In practice, ratings of 7 to 8 indicate highly functioning wall elem ents that are only beginning to show the first signs of distress or weathering. For exam ple, a ten-year-old soldier pile wall ma y have m oderately extensive m inor surface corrosion on piles where protective paint has weathered and peeled, and m ay have wood lagging beginning to split. Distresses are very low overall, present over a m odest am ount of the wall, and do not require im me diate or near-term attention. 5 to 6 Fair High extent of low severity distress and/or low-to-m edium extent of m edium to high severity distress. Distress present does not com prom ise element function, but lack of treatment may lead to impaired function and/or elevated risk of elem ent failure in the near term . In practice, ratings of 5 to 6 indicate functioning wall elem ents with specific distresses that need to be m itigated in the near-term to avoid significant repairs or element replacement in the longer term. For exam ple, num erous anchor struts holding MSE wire facing elem ents in place are be ginning to break due to corrosion and suspected over-stressing of the connections at the tim e of construction. Although the overall functi on of the reinforced earth wall is not in jeopardy, failing wall facing baskets are allowi ng faci ng fi ll to spill out. If several overlying baskets experience this isolated element failure, significant wall face sag and deformation may result at the top of the wall, eventually im pacting the overlying guardrail installation. This ele me nt should be inspected carefully along the entire wall and repaired as needed to forestall further facing basket deterioration. 3 to 4 Poor Medium-to-high extent of medium-to-high severity distress. Distress present threatens elem ent function, and strength is obviously com prom ised and/or structural analysis is warranted. The element condition does not pose an immediate threat to wall stability and closure is not necessary. In practice, a rating of 3 to 4 indicates marginally functioning, severely distressed wall elements in jeopardy of failing without element repair or replacem ent in the near-term . For exam ple, mo rtar throughout a historic stone ma sonry wall is cracked, spalling, highly weathered, and often m issing. Individual stone blocks are mi ssing from the wall face, and adjacent blocks show signs of outward displacem ent. Although not an immediate threat to overall wall stability, stone block replacement and repointing throughout the wall in the near-term are necessary to forestall rapid wall deterioration. 1 to 2 Critical Medium-to-high extent of high severity distress. Element is no longer serving intended function. Element performance is threatening overall stability of the wall at the time of inspection. In practice, a rating of 1 to 2 indicates a wall that is no longer functioning as intended, and is in danger of failing catastrophically at any time. For example, a 15-ft- tall cast-in-place concrete cantilever wall has a large open horizontal crack running the full length of the wall at the base of the stem . Vertical cracks are also beginning to open up in the wall face. Water is seeping from most wall cracks, and is running from the basal horizontal crack at several locations . The wall face has rotated outward, resulting in a negative batter of several degrees. The overlying guardrail is highly distorted above the wall and the adjacent roadway is showing significant settlement above the retained fill. The wall is in imminent danger of fa iling catastrophically, requiring the overlying roadway be closed to all traffic until the wall can be replaced or retained soil backslope can be stabilized. Source : DeMarco et al. (2010b). TABLE 6 NUMERICAL CONDITION RATING DEFINITIONS FOR WALL ELEMENTS IN FHWA WALL INVENTORY PROGRAM

13 • Joint spacing • Condition of “v-ditch” (i.e., drainage way at top of wall) • Coping deterioration • Drainage runoff • Drainage at the front of the wall. A rating scale ranging from zero to 9 (consistent with most bridge assessment procedures) is provided to describe the extent or severity of each feature. For example, with respect to loss of backfill, the following ratings descriptions are used: (zero)—backfill loss has resulted in significant settlement of the v-ditch or roadway or has affected wall inclination or alignment; (3)—significant areas/quantities of backfill loss are visible; (6)—backfill loss is occurring, but only minor areas/ quantities of backfill loss are visible; and (9)—no visible evi- dence of backfill loss. Numeric rating descriptions are unique to each type of feature or condition being assessed and can be found in the materials in Appendix E (web-only). The MSE wall inspection program in Ohio has focused data collection activities on observed problems, particularly sand leaking from joints, settlement of panels (largely from erosion of underlying support), uncontrolled drainage, and deteriorating panels (Narsavage 2006). The inspection pro- gram focuses on 23 potential symptoms (e.g., signs of water flow along the base of the wall) associated with wall joints, wall facing, drainage, and conditions at the top of the wall (see inspection form in web-only Appendix E). Condition ratings consist of simple “yes” or “no” responses. After its first inspection effort completed in 2006, Ohio reported that of the state’s 339 inspected walls, nearly one-third exhib- ited backfill migrating through wall joints and 13% exhibited some type of erosion problem. Utah’s MSE wall data collection largely follows the Ohio model. As shown on the inspection form provided in (web- only) Appendix E, data collection efforts focus on features and conditions believed to affect or reflect wall performance; namely, drainage, wall joints, wall facing, conditions at top of wall, foundation conditions and external stability, corrosion • Wall or parts of it out of plumb, tilting, or deflected • Bulges or distortion in wall facing • Some elements not fully bearing against load • Joints between facing units (panels, bricks, etc.) are misaligned • Joints between panels are too wide or too narrow • Cracks or spalls in concrete, brick, or stone masonry • Missing blocks, bricks, or other facing units • Settlement of wall or visible wall elements • Settlement behind wall • Settlement or heaving in front of wall • Displacement of coping or parapet • Rust stains or other evidence of corrosion of rebar • Damage from vehicle impact • Material from upslope rockfall or landslide adding to load on wall • Presence of graffiti (slight, moderate, heavy) • Drainage channels along top of wall not operating properly • Drainage outlets (pipes/weepholes) not operating properly • Any excessive ponding of water over backfill • Any irrigation or watering of landscape plantings above wall • Root penetration of wall facing • Trees growing near top of wall. Another data collection/wall inspection process has been developed by the Nebraska Department of Roads. In this meth- odology (Nebraska Department of Roads 2009), the MSE wall features that are assessed are: • Wall tilting • Structural cracking • Facial deterioration • Bowing of the wall • Panel staining • Exposure of fabric • Loss of backfill • Erosion in front of wall • Erosion in back of wall Rating Rating Definition 7 to 10 Good to Excellent No com binations of elem ent distresses are observed indicating unseen problem s or creating significant perform ance proble ms . No history of rem ediation or repair to wall or adjacent elem ents is observed. 5 to 6 Fair Som e observed global distress is not associated with specific elements. Some element distress com binations are observed th at indicate wall com ponent problems. Minor work on prim ary elements or major work on secondary elements has occurred improving overall wall function. 1 to 4 Poor to Critical Global wall rotation, sliding, settlement, and/or overturning are readily apparent. Combined elem ent distresses clearly indicate serious stability problem s with com ponents or global wall stability. Major repairs have occurred to wa ll structural elements, though functionality has not im proved significantly. Severe distresses are apparent on adjoining roadways. Source : DeMarco et al. (2010b). TABLE 7 WALL PERFORMANCE RATINGS

14 Wall panels shall be checked for cracking, spalling, other forms of deterioration, and collision damage. • Drainage systems through or along MSE walls should be inspected to verify water is free flowing into and out of the appropriate facility. • Ensure that weep holes are free draining. • Inspect all inlets to verify water is draining into the inlet, and flowing freely to the inlet and out of the outlet. Examine inlets for cracks. • Inspect visually or use down hole cameras (as appropriate) for all culverts and pipes contained or having portions in, behind, or above the MSE wall mass and for pipes or culverts which run above, adjacent to, or outlet through the MSE walls to ver- ify pipes are free draining and water is flowing through (and not under or around) the pipe. Examine drainage pipes for cracking or damage with emphasis on areas where water may flow, or is flowing, into the MSE wall soil mass. Inspect outlet ends to verify free drainage or for evidence of migration of fill or other material. • Inspect swales above the MSE wall. Verify rock fall or other materials (trees, etc.) are not blocking, redirecting, or restrict- ing the flow of water through the drainage ditch above the MSE wall to the appropriate receptacle. • Inspect collection and outlet basins to verify water is draining freely. Look for any signs of infiltration or migration of mate- rial which may prevent water from draining from the wall. • Identify inappropriate appearance of water along the base of the wall (i.e., if water is appearing when weather conditions have been particularly dry). Note areas where there is inappropriate collection and/or lack of drainage for water along the length of the MSE wall. • Note erosion of soil along the base of the wall exposing or undermining the leveling pad. In the Pennsylvania methodology, observed conditions are then translated into ratings (shown in Table 8) that are assigned to the following MSE wall elements/items: • Anchorage • Backfill • Wall conditions such as bulging, joint conditions, dete- rioration of face panels, connection of the backs, etc. • Panels • Drainage • Foundation • Parapets. Data collection and inspection schemes are inherently rooted in the experience and judgment of their developers. In the city of Seattle, Washington, for example, instances of and degradation, impact and collision, and miscellaneous issues. As in Ohio, condition ratings consist of simple “yes” or “no” responses; however, the extent of the symptom/issue is quantified as a percentage of the total wall. Some of Utah’s inspection queries relate directly to two-stage MSE walls, which are widely used in the state. The Pennsylvania DOT (PennDOT; see Pennsylvania Department of Transportation 2010) has a well-defined retain- ing wall inspection program conducted in conjunction with its bridge inspection program. (Bridge and retaining wall data are maintained in the same management system.) The program involves all walls, not just those at bridges. One wall element receiving particular focus in PennDOT’s inspection process is a button-head connection present in some first-generation MSE walls, because the cold-formed button head details were found to develop micro-cracks that contributed to the failure of the button head. The following directives relating to MSE walls are specified in the PennDOT inspection manual: Mechanically Stabilized Earth (MSE) retaining walls should be inspected for evidence of wall movement. • Examine barrier and moment slab for evidence of movement as well as the MSE wall for evidence of bulging, bowing, or panel offset. • Perform a survey if movement is suspected to compare to ini- tial inspection data to gauge amount of movement. • Examine the roadway above MSE walls for indications of fail- ing pavement or tension cracking. These may indicate a loss of fill. For MSE walls in front of sloping backfill, the crest of the embankment should be investigated for soil stress or failure, both of which may indicate settlement or wall movement. The joints between panels of MSE walls are to be inspected and examined for loss of backfill, change in spacing, and indications of settlement. The specification requirement for joint spacing is a maximum three-quarters of an inch. • Inspect walls for evidence of backfill loss (piles of aggregate at the base of the wall). • Indicate visibility of backfill or fabric behind the panel through joints. • Examine for evidence of damage to the geotextile fabric, if visible. • Look for variation in joint spacing. Note vegetation growing in joints. • Vertical slip (expansion joints) used on long lengths of walls should be investigated similar to panel joints. The initial spac- ing at the slip joint should be determined from design, shop, or as-built drawings. Rating Rating Definition 8 Good condition. No apparent problems. 6 Satisfactory condition. Structural elements sound. Localized drainage problems, settlement, staining, washing of fines from backfill material. 4 Poor condition. Localized buckling, deteriorated face panels, joint problems, major settlement, ice damage. 2 Critical. Major structural defects, components have moved to point of possible collapse. TABLE 8 PERFORMANCE RATINGS ASSIGNED TO WALL ELEMENTS IN PENNSYLVANIA INSPECTION/ASSESSMENT PROCESS

15 Other examples of using new technologies to monitor the performance of MSE walls include the incorporation of fiber-optics into geosynthetic reinforcement (Lostumbo and Artieres 2011). Various structural health monitoring tools now being built into bridges can readily be adapted for retaining walls. New technologies such as these will become increasingly more common in wall performance data collec- tion and assessment efforts. The general state of practice with respect to which MSE wall features or components are examined during data col- lection activities, based on survey respondents, is shown in Table 9. Only three of the 17 respondents to the associated survey question reported having some type of inventory. Responses suggest that the wall features or conditions most frequently examined by agencies are wall plumbness, bulg- ing or distortion of the wall facing, and cracking of facing elements. As can be seen subsequently in Table 16, these features/conditions correlate well to those distress/failure modes which are believed most important or significant rela- tive to wall performance. Eight of the 11 responses pro- vided as “other” features were simple declarations that the particular respondent did not collect any such data. Two more adverse retaining wall performance were observed to accom- pany (or even be manifest as) excess wall tilt. Consequently, wall tilt measurements using a digital protractor are a princi- pal component of Seattle’s inspection program (Molla 2009). To help ensure comparable and consistent data, tilt mea- suring stations are permanently established on many walls. Another example of how experience affects data collection activities is the scope and frequency of inspections speci- fied for MSE walls in Pennsylvania. An in-depth inspection including a three-dimensional spatial survey of the wall is required every 10 to 15 years. This requirement arises largely from global stability and creep concerns stemming from local geologic conditions in the state—more particularly along Route 22/322 in Lewistown Narrows, where one of the longest MSE walls in the United States has been con- structed. PennDOT has also implemented new technology as part of its data collection efforts. In 2008 and 2009, Lidar technology using a fixed-wing aircraft was used to assess the amount of creep that the Lewiston Narrows wall was expe- riencing. Unfortunately, the goal of 0.10 ft (30 mm) proved difficult to confirm because of the low altitude required within the canyon. The technology may be retried using a helicopter instead. Only Agencies with Inventories All Respondents to Particular Question Response Number Percent Number Percent Wall plumbness 2 67 5 29 Bulging or distortion of wall facing 2 67 5 29 Alignment and spacing of joints between facing elements 2 67 4 24 Cracking of facing elements 2 67 5 29 Damage to corners of facing elements 2 67 4 24 Damage from vehicular impact 1 33 3 18 Settlement along line of wall 1 33 4 24 Settlement behind wall 1 33 4 24 Distress in ground or pavement in front of wall 1 33 2 12 Distress in ground or pavement behind wall 1 33 3 18 Displacement of coping or parapet 2 67 3 18 Rust stains or other external evidence of corrosion 1 33 3 18 Functionality of drainage/catch basin 1 33 2 12 Functionality of internal drainage features (e.g., weepholes and piping) 1 33 2 12 External erosion 2 67 3 18 Internal erosion of backfill 1 33 2 12 Changes to wall geometry (e.g., excavation at toe, add surcharge load) 1 33 3 18 Vegetation growth 0 0 1 6 Internal corrosion/degradation of reinforcement 1 33 2 12 Other (specify) 0 0 11 65 TABLE 9 MSE WALL FEATURES AND/OR CONDITIONS ASSESSED AS PART OF DATA COLLECTION AND MONITORING ACTIVITIES (multiple responses possible)

16 conducted “in the absence of any special condition or cir- cumstance that makes it prudent to inspect more often”). Selection of an inspection interval for a specific wall involves considerations of any known occurrence of adverse perfor- mance; wall age (older walls may require more frequent inspections); presence of questionable backfill (that may lead to settlement or internal corrosion concerns); and occur- rence of flooding, earthquake, or vehicle damage. Principles of risk management dictate that walls whose failure would produce significant consequences are candidates for more frequent inspection. When survey respondents were asked, “Which of the following statements best describes your agency’s MSE wall performance monitoring activities?” (as shown in Table 10), the overwhelming response was that such activities were gen- erally in response to specific instances of adverse performance. The remainder indicated that assessments were performed, but not always including all MSE walls in their inventory. This appears to suggest that, contrary to the practices and recom- mendations previously discussed, the frequency of monitoring activities appears to be largely driven by resource availability and/or in response to incidents of adverse performance. Table 11 summarizes some interrelationships between those agencies that have reported the establishment of MSE wall inventories, the extent of those inventories, and the nature of their ongoing monitoring activities. As can be seen in this table, more than half of the agencies reporting MSE wall inventories only monitor their walls in response to known incidents of adverse performance. Just over one- quarter of agencies having inventories regularly inspect or assess most or all of those walls. From these data, it appears that once MSE wall inventories are initially developed, additional information relative to ongoing performance is generally either not collected or not assessed for most walls. (As pointed out previously, there is no uniform standard for designating and counting MSE walls). COLLECTION OF CORROSION AND DEGRADATION DATA A distinguishing feature of MSE walls relative to other retain- ing wall types is the reinforcement in the retained soil mass. The stability of the wall depends on the integrity of the reinforce- of these responses indicated that feature assessment was only performed in response to observed wall distress, while the remaining response clarified that wall features were exam- ined as part of their bi-annual bridge inspection activities. FREQUENCY OF FIELD INSPECTIONS AND MONITORING ACTIVITIES The condition and performance of MSE walls vary over time. Because of this, it is important that data collection and assessment activities be conducted routinely. According to the NBIS, bridges are inspected at two-year intervals. Some agencies have adopted similar two-year inspection intervals for retaining walls. Other agencies such as New York City require privately owned retaining walls to be inspected every five years. Kansas typically assesses its MSE walls at three- year intervals, whereas Oregon’s plan calls for inspection of “good” walls of all types every five years, and “fair” or “poor” walls more often. Between 1986 and 1997, California had established five- to ten-year inspection intervals for MSE wall elements, particularly internal reinforcement elements. PennDOT takes a tiered approach, with a “routine” wall inspection every five years and an “in-depth” inspection (which includes a three-dimensional survey for MSE walls more than 100 ft long and more than 20 ft high) at either 10- or 15-year intervals. Unscheduled “special” inspections are to be performed after a significant event, such as a vehicular collision, extreme weather, or indication of wall movement. Similarly, the FHWA’s WIP directs that all walls should be inspected on a maximum 10-year cycle, and walls having performance issues are subject to more frequent inspection and assessment work, particularly those subject to “qualify- ing emergency relief events” such as a landslide or flood. PennDOT defines a routine inspection as “a close visual and hands-on examination of retaining walls and their drainage systems without traffic control. Those portions which cannot be accessed safely from beyond the edge of pavement are viewed using binoculars and/or a digital camera.” In con- trast, an in-depth inspection consists of “a close visual and hands-on examination of retaining walls and their drainage systems. Use of down-hole cameras or visual inspection of larger pipes is required for the drainage system.” Based on their study, Brutus and Tauber recommend a five-year interval for routine inspections (i.e., inspections Response Number Percent Reactive to reported incidents of adverse performance 32 73 Irregular inspection/assessment of some MSE walls 3 7 Regular inspection/assessment of some MSE walls 4 9 Irregular inspection/assessment of most or all walls in inventory 1 2 Regular inspection/assessment of most or all walls in inventory 4 9 TABLE 10 BEST DESCRIPTION OF AGENCY’S MSE WALL PERFORMANCE MONITORING ACTIVITIES

17 thickness loss, as well as decreases in tensile strength. With electrochemical methods, potential and polarization resis- tance measurements are made and correlated with dimen- sions of the reinforcement. In Corrosion/Degradation of Soil Reinforcements for Mechanically Stabilized Earth Walls and Reinforced Soil Slopes, a principal reference in the United States regarding the degradation and corrosion of MSE wall reinforcement, Elias et al. (2009) advise that “given the advan- tages, utilization of remote electrochemical methods is highly recommended with at least some coupons buried for retriev- als to confirm results.” Their provided rule of thumb regard- ing installation is two locations spaced at least 200 ft (60 m) apart for MSE walls 800 ft (250 m) or less in length and three locations for longer walls. At each location, corrosion should be monitored at a minimum of two depths. For extractible cou- pons (i.e., inspection wires), Caltrans has developed a typical layout of 18 clustered coupons to be periodically extracted (see appendix in Fishman and Withiam 2011). Caltrans has also developed a set of extraction guidelines (California Depart- ment of Transportation 2004). With respect to frequency of assessing corrosion, Elias et al. (2009) recommend that potential and polarization resis- tance measurements (owing to their sensitive nature) be made monthly for the first three months, bi-monthly for the next nine months, and annually thereafter. This recommended frequency is significantly greater than the frequency at which other wall inspection and data collection activities occur (as described in the previous section). Extractible coupons are typically removed at five- to 15-year intervals, depending on the number of coupons installed. In California’s typical ment, which can be either relatively extensible geosynthetic materials or inextensible metallic straps or meshes. Because of the reinforcement’s criticality, many MSE performance assess- ments focus on the reinforcement, which can be challenging since the reinforcement is buried and not directly observable. Also problematic is corrosion, which is a rate process affected by multiple factors. If certain other factors are assumed, wall age might serve as a proxy parameter for corrosion and remain- ing service life. However, premature failures illustrate potential shortcomings of relying on such assumptions. Several U.S. state agencies have undertaken reinforce- ment corrosion studies. Table 12 presents a brief summary, slightly expanded from that prepared and presented by Fish- man and Withiam (2011) of these various efforts. It can be noted that the corrosion issues reported in Nevada resulted from a now-outdated backfill specification rather than cur- rent AASHTO backfill specifications, and care must be taken when interpreting adverse performance of walls constructed using early design methods. Detailed descriptions of the corro- sion monitoring activities of California, Florida, New York, and North Carolina are presented in Elias et al. (2009). It is interesting to note the correlation between agencies that have developed MSE wall inventories and those that have expe- rienced MSE wall corrosion issues (and have subsequently developed monitoring programs). Corrosion monitoring of steel reinforcement is typically accomplished by either retrieval of buried coupons or non- destructive electrochemical methods. With exhumed coupons, corrosion can be assessed by determining weight and section Agency Num ber of Walls Percent Walls in Inventory Best Description of Monitoring Activities Alberta, Canada 3 00 10 R eactive to reported incidents of adverse perform ance California 4 00 75 R eactive to reported incidents of adverse perform ance Colorado 800 60 R eactive to reported incidents of adverse perform ance Kansas 300 50 Regular inspection/assessment of most or all walls in inventory Minnesota 300 60 Reactive to reported incidents of adverse performance Missouri 899 100 Reactive to reported incidents of adverse performance Nebraska —1 10 Regular inspection/assessment of most or all walls in inventory New York 635 100 Regular inspection/assessment of most or all walls in inventory 2North Carolina 75 97 Regular inspection/assessment of most or all walls in inventory North Dakota 100 100 Irregular inspection/assessment of most or all walls in inventory Ontario, Canada 500 100 Regular inspection/assessment of some MSE walls Tennessee 1000 50 Reactive to reported incidents of adverse performance Utah 700 80 Reactive to reported incidents of adverse performance Wisconsin 400 85 Reactive to reported incidents of adverse performance 1Data missing. TABLE 11 RELATIONSHIPS BETWEEN THOSE AGENCIES WITH MSE WALL INVENTORIES, THE SCOPE OF THOSE INVENTORIES, AND NATURE OF ONGOING MONITORING ACTIVITIES

18 State Description California Has been installing inspection elements with new construction since 1987, and has been perform ing tensile strength tests on extracted elements. Some electrochemical testing of in-service reinforcements and coupons has also been performed. Linear polarization resistance (LPR) and EIS tests were performed on inspection elements at selected sites as part of NCHRP Project 24-28 and results compared with direct physical observations on extracted elements. Florida Program focused on evaluating the impact of saltwater intrusion, including laboratory testing and field studies. Coupons were installed and reinforcements were wired for electrochemical testing and corrosion monitoring at 10 MSE walls. Monitoring has continued since 1996. Georgia Began evaluating MSE walls in 1979 in response to observations of poor performance at one site located in a very aggressive marine environment incorporating an early application of MSE technology. Exhumed reinforcement samples for visual examination and laboratory testing. Some in situ corrosion monitoring of in-service reinforcements and coupons at 12 selected sites using electrochemical test techniques was also performed. Kentucky Developed an inventory and performance database for MSE walls. Performed corrosion monitoring including electrochemical testing of in-service reinforcements and coupons at five selected sites. Nevada Condition assessments and corrosion monitoring of three walls at a site with aggressive reinforced fill and site conditions. Exhumed reinforcements for visual examination and laboratory testing; performed electrochemical testing on in-service reinforcements and coupons. A total of 12 monitoring stations were dispersed throughout the site providing a very good sample distribution. New York Screened inventory and established priorities for condition assessment and corrosion monitoring based on suspect reinforced fills. Two walls with reinforced fill known to meet department specifications for MSE construction are also included in program as a basis for comparison. Corrosion monitoring uses electrochemical tests on coupons and in-service reinforcements. North Carolina Initiated a corrosion evaluation program for MSE structures in 1992. Screened inventory and six walls were selected for electrochemical testing including measurement of half-cell potential and LPR. This initial study included in-service reinforcements, but coupons were not installed. Subsequent to the initial study, NCDOT has installed coupons and wired in-service reinforcements for measurement of half-cell potential on MSE walls and embankments constructed since 1992. LPR testing was also performed at approximately 30 sites in cooperation with NCHRP Project 24-28. Ohio Concerned about the impact of their highway and bridge de-icing programs on the service life of metal reinforcements. Performed laboratory testing on samples of reinforced fill but did not sample reinforcements or make in situ corrosion rate measurements. Oregon Preliminary study including (1) a review of methods for estimating and measuring deterioration of structural reinforcing elements, (2) a selected history of design specifications and utilization of metallic reinforcements, and (3) listing of MSE walls that can be identified in the ODOT system. Utah Extracted 22 wire coupons from one- and two-stage MSE walls all approximately 11 to 12 years old. Galvanization thickness was found to still be greater than initial specified values. Data to provide baselines for future assessments. After Fishman and Withiam (2011). TABLE 12 SUMMARY OF US STATE MSE WALL CORROSION ASSESSMENT PROGRAMS

19 year intervals for a minimum of four retrievals, or one-third the expected life of the facility. The state of practice for assessing degradation and corro- sion in MSE walls, as indicated by 14 survey participants who provided specific responses, is shown in Table 13. Three of these respondents indicated that they have their own MSE wall inventories. Based on the information presented in this table and in Table 12, it appears that a minority of agencies assesses corrosion of metallic MSE wall reinforcement, and none sys- tematically assess degradation of geosynthetic reinforcement. installation, coupons are removed and inspected after five, ten, 20, 30, 40, and 50 years. For geosynthetic reinforcement, the primary performance issue is polymer degradation. At present, the only effective means of assessment is retrieval of buried specimens. The assessment process involves successive retrieval and testing of samples to determine both mechanical and chemical proper- ties. Strength and elongation (i.e., creep) properties can then be extrapolated to predict future performance. Elias et al. (2009) recommend that sampling and testing occur at five- to seven- Only Agencies with Inventories All Respondents to Particular Question Response Number Percent Number Percent Do not currently assess 2 67 12 86 Linear polarization resistance (LPR) for metallic 0 0 1 7 Extractible coupons for metallic 1 33 2 14 Exhumation for geosynthetic 0 0 0 0 Other (specify) 0 0 0 0 TABLE 13 METHOD(S) CURRENTLY USED BY AGENCIES TO ASSESS DEGRADATION/CORROSION OF REINFORCEMENT (multiple responses possible)

20 After wall condition and performance data have been col- lected, assessments can be performed to determine how well MSE walls are meeting their performance objective(s). Assess- ments can also be performed to prioritize maintenance and replacement functions. [As a reference, FHWA (1999) has developed a basic primer regarding assessment manage- ment concepts while Bernhardt et al. (2003) have discussed application of these concepts to “geotechnical infrastructure” assets.] Such assessments commonly involve some type of numerical scale or standard set of terms. These scales or terms can be used in quantitative rating algorithms and/or more sub- jective, qualitative expressions of wall performance. Ideally, these scales ultimately link current wall performance with the wall’s position within its design life cycle. This chapter will discuss how wall performance data are assessed and then used for asset management. ASSESSMENT AND INTERPRETATION OF DATA Referring again to the established and tested FHWA’s WIP, the wall element and performance data collected (as discussed in the previous chapter) are combined with factors measuring the relative importance of each element to establish a final overall wall condition rating, which ranges from 5 to 100. Conver- sion of this numeric rating to a qualitative description can be approximately achieved by dividing the rating by 10 and com- paring it to the element and wall performance rating definitions shown in Table 6 and Table 7, respectively. Although their origin is not explicitly stated, it appears that the weighting factors used in the WIP were established by some type of consensus of experienced persons. The pro- cedure manual states, “these element weightings have been determined to sufficiently discern element impacts on wall performance. However, as more wall inventory data are col- lected, weightings will be re-evaluated for appropriateness, and altered as needed to provide meaningful and consistent wall condition ratings.” The FHWA WIP wall condition rating was also cited by Brutus and Tauber (2009) in their consideration of how to quantify wall performance. They also provided the five-point rating scale in Table 14 as another possible sample rating system. In some numeric schemes, adverse performance is indicated by a low rating, whereas in others a low score is desirable. Some MSE wall assessments do not incorporate a type of condition rating, numeric or otherwise. For example, state agencies in Utah and Ohio currently document only the existence of certain adverse conditions. As part of this synthesis, 44 survey participants provided feedback regarding how important they thought particular wall features and conditions are in assessing the long-term perfor- mance of MSE walls. These beliefs are in large measure repre- sentative of the relative importance of specific wall condition data and might function similarly to the FHWA WIP weighting factors in a current assessment or prediction of future wall per- formance. In the survey, relative importance was distinguished using a numerical rating scale where 1 = not important, 2 = mildly important, 3 = moderately important, 4 = very impor- tant, and 5 = most important. The results in terms of average rating are shown in Table 15. Also shown is the variance for each feature from the overall mean rating, helping indicate each feature’s perceived importance relative to the others. As can be seen in the table, features associated with drain- age (both external and internal) typically are considered to be among the most important. Changes to wall geometry resulting from excavation or addition of surcharge load that would affect global stability are also viewed as being rela- tively important. Most important, however, is corrosion and degradation of internal reinforcement. This result appears to be consistent with the impetus for the initial establishment of many existing MSE wall inventories—concerns relative to, or premature failures stemming from, corrosion of MSE wall reinforcement. Interestingly, a small panel of MSE wall experts convened by the Utah DOT judged that drainage issues are the most significant issues during the first 15 years or so of wall life, after which corrosion issues become the most important (Bay et al. 2009). Perhaps most surprisingly, the survey indicated that wall height is considered among the least important—surprising because this parameter is among the more frequently included parameters in wall inventories. This also appears inconsistent with the assessment of Brutus and Tauber (2009) that the most important component contributing to risk stemming from wall failure is the height of the wall. Also surprising is that wall age (as implied from date constructed) is rated as being below aver- age in importance because internal corrosion (the most impor- tant factor) is itself a function of age. CHAPTER FOUR ASSESSMENT AND USE OF MECHANICALLY STABILIZED EARTH WALL DATA

21 Rating Description Excellent No significant indication of distress or deterioration. Good Some indications of distress or deterioration, but wall is performing as designed. Fair Moderate or multiple indications of distress or deterioration affecting wall performance. Poor Significant distress or deterioration with potential for wall failure. Critical Severe distress or deterioration. Indications of imminent wall failure. Source: Brutus and Tauber (2009). TABLE 14 SAMPLE RATING SYSTEM FOR WALL PERFORMANCE Response Mean Variance Internal corrosion/degradation of reinforcement 4.4 +0.9 Internal erosion of backfill 4.1 +0.7 Wall geometry changes (e.g., excavation at toe, added surcharge load) 4.1 +0.6 Functionality of internal drainage features (e.g., weepholes and piping) 4.0 +0.6 Drainage conditions 4.0 +0.6 Proximity of external water sources (e.g., river, sprinklers, etc.) 3.9 +0.4 Distress in ground or pavement behind wall 3.8 +0.4 Functionality of drainage/catch basins 3.8 +0.3 Bulging or distortion of wall facing 3.7 +0.2 Maximum wall height 3.7 +0.2 Cracking of facing elements 3.6 +0.2 Settlement behind wall 3.6 +0.2 Reinforcement type 3.6 +0.1 Location and condition of drainage discharge points 3.5 +0.1 Rust stains or other external evidence of corrosion 3.5 +0.1 Distress in ground or pavement in front of wall 3.5 +0.1 External erosion 3.5 +0.1 Embedment of wall 3.5 +0.0 Post-construction modifications 3.5 +0.0 Settlement along line of wall 3.5 +0.0 Slope behind wall 3.4 +0.0 Damage from vehicular impact 3.4 +0.0 Slope in front of wall 3.3 –0.1 Alignment and spacing of joints between facing elements 3.3 –0.1 Wall plumbness 3.3 –0.2 Wall type 3.3 –0.2 Damage to corners of facing elements 3.2 –0.3 Presence of bench at toe of wall founded on slope 3.2 –0.3 Road/traffic offset 3.1 –0.3 Displacement of coping or parapet 3.0 –0.4 Date constructed 3.0 –0.5 Manufacturer 2.7 –0.7 Vegetation growth 2.7 –0.7 Average wall height 2.6 –0.8 Wall length 2.3 –1.2 TABLE 15 RELATIVE IMPORTANCE OF WALL FEATURES/CONDITIONS IN ASSESSING THE LONG-TERM PERFORMANCE OF MSE WALLS

22 In addition to the relative importance of certain wall features and conditions, survey participants were also asked to rate how significant they thought certain potential failure/distress modes were relative to the long-term performance of MSE walls. The failure/distress modes were those typically considered in wall design procedures. Significance was rated on a scale of 1 = not significant, 2 = mildly significant, 3 = moderately significant, 4 = very significant, and 5 = most significant. The results, shown in Table 16, indicate that most agencies believe that global stability and reinforcement rupture are the most likely failure modes for MSE walls in the long term. The term “reinforce- ment rupture” was not specifically defined, but is believed to have been interpreted to include failures resulting from both section loss and subsequent overstressing as well as overstress- ing of the initial section. The data also suggest that agencies believe overturning and facing failure are the least likely failure modes. This information is important in that these beliefs con- stitute a type of expert opinion that can be used in MSE wall service life prediction methods as well as in wall failure risk assessments. Both of these activities currently appear to be in their naissance, as discussed later in this chapter. USE OF PERFORMANCE ASSESSMENTS IN DECISION MAKING Once wall conditions are assessed and its condition quanti- fied on some basis (such as the FHWA WIP wall condition rating), the assigned rating can be used in more than one way for programming decisions. In some systems, the numeric value can be directly related to a specified action level (e.g., walls rated below 40 must be repaired). In other systems, the numeric value is used for ranking, and resources for items such as maintenance or repair are allocated accordingly (e.g., there is $100,000 in the budget for repairs, which walls do we start with?). In yet other systems, such as the FHWA WIP, the final overall rating is only one of several factors used to make pro- gramming decisions. The rating by itself is not directly related to a particular action. Rather, four additional items/questions are considered in the FHWA WIP: (1) are additional investiga- tions required (how reliable is our assessment); (2) what design criteria may have been used in planning the structure (was the structure engineered); (3) what aspects of the wall structure are historic or contribute to the cultural context of the road asset; and (4) what are the consequences of wall failure. These items are subjectively assessed by the person rating the wall with few objectively defined criteria; hence, programming decisions, to which wall condition ratings only partially contribute, are largely subjective in the FHWA WIP. As stated previously, some MSE wall assessments do not incorporate any condition ratings; therefore, some alternate means of decision making is required. On a comparative wall- to-wall basis, one can tally the number of adverse occurrences per wall and then rank the tallies to establish a type of prior- ity list. Swenson (2010) used the Utah wall inventory data and attempted to improve the ranking processes by associating particular conditions/issues with particular failure modes and then assigning weights to indicate criticality. Unfortunately, the expert input/consensus usually required to link conditions, failure modes, and consequences was limited. When asked about a specific methodology for assessing long-term performance of existing MSE walls, no survey respondent answered affirmatively beyond citing regular inspections or several corrosion assessment studies. These items appear to be contributing components to a methodology, but no fully developed methods were identified. From the responses gathered and review of available literature, it does appear that some agencies may rely largely on pre-approval product processes and compliance with Highway Innovative Technology Center criteria (see Highway Innovative Tech- nology Center 1998) for assurance that MSE walls will per- form adequately. Although such measures should improve the likelihood of good, long-term performance, failure case histories suggest that they are not failsafe. Estimation of Service Life In their study, Brutus and Tauber (2009) concluded that “there is no data available in technical literature on the estimate of designed service life or on construction or maintenance oper- ations on old retaining walls built somewhere between 50 to 100 years ago.” MSE walls in the United States are newer than this, yet this statement also appears to apply to those Response Mean Variance Global stability 4.3 +0.4 Reinforcement rupture 4.3 +0.4 Reinforcement pullout 4.2 +0.3 Loss of foundation support due to erosion 4.0 +0.1 Loss of foundation support to bearing capacity failure 4.0 +0.1 Excessive settlement 3.8 –0.1 Sliding 3.6 –0.3 Overturning 3.5 –0.4 Facing failure 3.3 –0.6 TABLE 16 RELATIVE SIGNIFICANCE OF POTENTIAL FAILURE/DISTRESS MODES IN LONG-TERM PERFORMANCE OF MSE WALLS

23 • Disruption of highway operations, including full or par- tial closure of the roadway, or appurtenant facilities; • Disruption of adjacent utility lines, such as water mains or electrical conduits; • Environmental consequences, such as damage to a sig- nificant wildlife habitat or blockage of a watercourse; and • Damage to cultural assets or sensitive land uses. Again, as outlined by Brutus and Tauber, the consequences of adverse wall performance or failure can be affected by: • The volume of earth retained by and otherwise contained in the wall, which in turn is most frequently reflected by the height of the wall; • The proximity of the wall ERS to the roadway or other potentially affected facilities or structures; • The intensity of usage of potentially affected facilities, such as traffic volume on a roadway or occupancy of a building; • The structural robustness of adjacent buildings and facilities; and • The vulnerability of occupants and/or users. Often the consequence of failure (either functional or structural) is also quantified or expressed in terms of some type of scale. Possible metrics include monetary losses, inju- ries or fatalities, and/or decrease in levels of serviceability. Brutus and Tauber suggest use of a three-level rating system such as that shown in Table 17. Performance of risk assessments for MSE walls at pres- ent appears to be problematic. Risk assessments (particularly probabilistic ones) typically require the use of “expert opin- ion” or “expert consensus”; however, being expert requires being experienced. As agencies continue to monitor wall performance, they will gain further experience, and with this increased experience, their ability to assess risk will improve; hence it is in this manner that methods for risk assessment are likely to evolve. Wall function as reflected in inventory inclusion criteria such as that shown in Table 2 would be of particular importance when executing risk assessments. newer MSE walls that have intended design lives of 75 to 100 years. As reported in the previous section, none of the agencies surveyed had a specific methodology for assessing long-term performance of existing MSE walls, let alone a method for estimating design life. Brutus and Tauber do however suggest two approaches that might be used to estimate the remaining service life of walls. One approach is to perform repeated inspections and “chart escalating maintenance and repair costs to project a remaining service life . . . using some criterion such as when the repair and maintenance costs exceed more than 50% of the replacement cost.” The other approach is to assess the performance of simi- lar walls (e.g., same construction standards) built over a long period of time and use the observed performance to forecast the performance of newer walls. However, care must be taken when interpreting adverse performance of walls constructed using different, older design methods that may not be represen- tative of newer walls. Elements of these approaches are now beginning to be implemented with the development of MSE wall inventories and the collection of data as described in the previous chapters. As pointed out previously, the development of initial inventories appears to be progressing much more rap- idly than regular ongoing performance data collection. Risk Assessment Tied closely to the assessment of wall performance is the assessment of risk. Sometimes, risk assessment is not explic- itly undertaken, particularly if wall performance appears more than adequate. Ultimately however, it is questions of risk and consequence of adverse performance that drive many asset management activities. Potential consequences of failure that are considered in the performance of risk assessments include (Brutus and Tauber 2009): • Death or injury to persons, including facility users and those on adjacent properties or facilities; • Damage to property including vehicles, highway prop- erty or facilities, and adjacent property or facilities; Rating Description Severe High likelihood of injuries or death fro m debris falling on a heavily traveled roadway, on other heavily used adjacent areas, or from collapse of structures near top of wall. High likelihood of extensive or total-loss damage to vehicles or structures. Complete closure of a heavily traveled roadway requiring lengthy detours. Significant Low probability of injury to persons but likelihood of any of the following: (a) substantial property damage, (b) interruption of water or other utility service to a large area, (c) lengthy blockage of access to business properties or public facilities, (d) long - term damage to environmental or cultural re sources, (e) closure of two or more lanes of a heavily traveled roadway, (f) full closure of any roadway with no alternative access or requiring lengthy detours. Minor Low probability of injury to persons or of damage to vehicles or non-highway property or facilities. Full roadway closures where alternative access is available. Closure of a single lane on a heavily traveled roadway. Source : Brutus and Tauber (2009). TABLE 17 SAMPLE RATING SYSTEM FOR CONSEQUENCES OF FAILURE

24 As MSE wall performance is monitored, assessments can be made regarding the adequacy of the wall’s design, construc- tion, and maintenance. These assessments can in turn be used to change practices and policies with the intent of improving wall performance, particularly for future walls. The feedback loop thus established becomes a means of continual improve- ment. One example of this process is the development and recent release of NCHRP Report 675, LRFD Metal Loss and Service-Life Strength Reduction Factors for Metal-Reinforced Systems (Fishman and Withiam 2011), in which the accumu- lation of reinforcement corrosion data over time has led to the development of more accurate metal loss models. This chap- ter discusses actions taken by survey respondents to improve the long-term performance of their MSE walls. These actions reflect lessons learned relative to design, construction, and maintenance. Ideally, these actions will lead to a decreased likelihood of failure or adverse performance of MSE walls in the long term. POLICIES AND PRACTICES DEVELOPED TO IMPROVE PERFORMANCE OF MECHANICALLY STABILIZED EARTH WALLS Survey participants were asked to respond regarding any approaches, besides monitoring, that their agency may have developed or implemented to improve the long-term perfor- mance of their MSE walls. Specific responses were sought relative to the following categories: • Regularly scheduled cleanout/maintenance of catch basins • Different requirements for backfill immediately behind wall face as compared with remainder of reinforced backfill • Developed special drainage details at ends of MSE walls • Developed special drainage details behind MSE walls • Specified vertical and horizontal distances for discharge points and water sources • Increased wall embedment • Other design specifications • Contractor/installer qualifications • Construction inspection • Post-construction inspection • Other. Typically, fewer than half of survey respondents provided feedback in any one category. The responses provided are generally summarized in the following paragraphs. With respect to regularly scheduled cleanout and mainte- nance of catch basins, respondents reported no special actions being taken in this regard. The responses offered suggest that performance of this activity varies significantly between agen- cies, ranging from its being “done as a matter of course,” and being done routinely, to “hit and miss if they actually do it.” With respect to different requirements for backfill imme- diately behind wall face as compared with remainder of rein- forced backfill, seven agencies specifically specified use of open-graded, free-draining aggregate or rock immediately behind the wall face. With respect to developing special drainage details at ends of MSE walls, agency improvements included turn- ing the wall ends into the slope, concrete headwalls being used (presumably at culvert openings), “plating all drainage surfaces above and around wall; insuring drainage does not enter and saturate reinforced backfill,” and use of water- proofing membranes together with weep drains and dedicated drainage collection systems. In the related query regarding specification of vertical and horizontal distances for dis- charge points and water sources, one agency reports using 100-ft intervals and another emphasized assuring that drainage below and above wall is on concrete inverts and concrete aprons. With respect to developing special drainage details behind MSE walls, multiple respondents indicated they require some type of underdrain located at the wall face and/or in back of the reinforced soil zone. One respondent emphasized that non-frost-susceptible aggregate and drain pipes should be extended to a depth below frost penetration. Other practices include using a drain gutter, lined swale, or concrete plating at the top of the wall. Most responses referred to needs for direct water away from the wall and to a lower elevation. A couple of respondents indicated that they had added weep drains and/or strip drains at the wall–soil interface rather than relying on drainage through panel or block joints. Texas reports that it has developed an inlet standard to “best accom- modate inlets . . . and also convey the water out of the wall in the quickest fashion.” With respect to increased wall embedment, most partici- pants who provided a response in this category indicated that their practice involves embedding the wall foundation below the frost line or at least some minimum depth (the value of CHAPTER FIVE OUTCOMES AND LESSONS LEARNED

25 now requiring production testing of MSE backfill stockpiles on-site rather than just at the material source. With respect to post-construction inspection, no new devel- opments were reported beyond a few agencies that now make a complete inspection of the wall at the end of construction routine. One responding agency indicated having a three-year warranty period for its MSE walls. Two agencies (Kansas and New York) reported that they retain construction quality control/quality assurance data and point out that retaining such data has the potential to diagnose future problems if they arise. While not being a practice unique to agencies responding to this survey, use of an impervious membrane above the entire reinforced soil mass to prevent the migration of aggressive materials (such as salts used to de-ice the overlying pavement) was cited by several respondents as a means of protecting the reinforcement from corrosion/degradation. MOST IMPORTANT “LESSON LEARNED” As part of the survey conducted for this synthesis project, recipients were asked to give their opinion as to what is the most significant lesson learned by their agency with respect to the long-term performance of MSE walls. Responses varied from design and backfill specification to construction practices and post-construction drainage maintenance. Given the poten- tial significance of these responses—being the most important thing(s) learned—all responses are presented in Appendix C in their entirety. Although the scope of the responses was broad, certain topics appeared more frequently than others. The four most frequent topics (in order of decreasing frequency) mentioned were drainage, construction, backfill, and modular block issues. Approximately one-fourth of respondents indicated that the most important lesson learned by their agency was drain- age-related—as two respondents put it: “Drainage; drainage; drainage,” and “W-a-t-e-r: from any and all directions and sources.” Although these particular responses lack specific- ity, it is readily apparent that the two respondents believe that drainage is essential to the successful performance of MSE walls. Another respondent suggested that the most impor- tant lesson was “providing a sound and firm foundation for support of the wall; and providing proper drainage within the wall system and adjacent to the wall geometry.” Approximately one-fifth of respondents reported that the most important lesson they learned was construction-related. One pointed out that “the systems can last forever but must be designed and built correctly.” Similarly, another noted, “For the most part [my agency] has had very few problems with MSE structures. We do know that great care must be taken in constructing these structures. If you start wrong in the beginning you’ll always be seeing problems in the walls.” which is most frequently 0.6 m, but appears to range up to 1.2 and 1.5 m in northern states such as Minnesota and New Hampshire). Some agencies reported using increased embed- ment for walls founded on slope, with minimum depths con- forming to AASHTO design specifications or as needed to satisfy global stability requirements. Although not reported in the survey, recent inspection of Utah DOT MSE walls indicates that the 1.2-m-wide horizontal bench required by AASHTO to be placed at the base of MSE walls founded on slopes is frequently absent. A proposed alternative to the bench suggested that embedment depth be increased to pro- duce the same amount of distance from the buried base of the wall to the face of the slope had the bench been installed. New Brunswick reported that maintaining such benches was one of its most important lessons learned. Elsewhere in the survey, Texas reported that it strongly encourages that walls not be perched on slopes, and if a slope is to exist at the base of wall that the slope be limited to 6:1 or flatter in combina- tion with an increased wall embedment. With respect to other design specifications, responses var- ied greatly. Several respondents indicated that they were in the process of revising or had recently improved their speci- fications but did not provide details, although one respondent implied that the presence of regular specification and design manual updates in and of itself is a beneficial practice. The most frequently reported focus is on being more restric- tive in specifying backfill, particularly with respect to grada- tion, fines content, and physiochemical-electrical properties. (Interestingly, current research being performed by W.A. Marr as NCHRP Project 24-22, “Selecting Backfill Materials for MSE Retaining Walls,” aims to broaden current FHWA specifications for MSE wall backfills.) One respondent indi- cated an improved practice in using concrete level pads at the base of the wall. Although not reported in the survey, owing to some instances of adverse wall performance, some states (e.g., Ohio) discourage the use of acute corners for its MSE walls. Nearly all responses to the question of contractor/installer qualifications (11 out of 12) indicate that agencies use an approved (or pre-approved) list of products and/or vendors. However, only two respondents (Colorado and Oregon) explic- itly indicated that their specifications require wall system vendors to provide contractor training or that the contractor possess some type of previous training. Sixteen agencies responded with comments regarding con- struction inspection; only one indicated that it does not do con- struction inspection on a regular basis. Four of the responding agencies (Colorado, Minnesota, New York, and Texas) have developed manuals and/or provide specific training for MSE wall construction. Four agencies (Massachusetts, Michi- gan, Montana, and Nova Scotia) indicated that they require wall supplier/vendor/manufacturer personnel on-site at least some time during construction. One agency (Nevada) reports

26 Lessons involving either MSE wall backfill or modu- lar blocks accounted for about 14% and 10% of responses, respectively. With respect to backfill, one respondent replied, “Use of fine grained select fill has resulted in the migration of material out from behind walls. We have thousands of square foot of wall that was backfilled with this type of material. Many walls have shown distress as a result. We have coars- ened up the gradation of select fill to lessen the potential of fill migration.” When modular blocks were mentioned, it was usually in the context of durability and degradation because of roadway de-icing activities. According to one respondent, “By having a formal wall approval process we have limited the use of modular block wall systems and the deterioration of these facing elements due to deicing chemicals.” One of the more extensive commentaries provided by a survey respondent related to the deformation-tolerance of MSE walls, and has bearing on wall inspection activities: The outside may get ugly [but] it’s the inside that matters. We had an MSE ride a landslide downslope 32 ft back in the 1970s. It deformed significantly, but is still in service today. We have had several lose foundation support, but as long as they were able to move and readjust the stresses through deformation, with no loss of backfill, they have all been able to stay in service— some for decades. However, excessive consolidation settlement and internal drainage failures have led to issues with cavities and retainment loss. These MSE failed within months and had to be replaced. Amazing[ly] flexible, but only up to a limit. It’s what’s inside that counts. Although different agencies appear to have had varying experiences with MSE walls, the “most important lessons learned” do tend to focus on the topics of drainage, con- struction, backfill, and modular block issues. Considering the importance given these topics by survey respondents, those issues could be important focal points in the develop- ment of future MSE wall assessment and/or management activities.

27 Combining a literature review with a survey and interviews, this synthesis project has attempted to determine: • The current state of practice in assessing the performance of mechanically stabilized earth (MSE) walls, particu- larly in the long term; • The direction of the state of practice; • What the current and effective practices are; and • What areas need improvement and/or research. Key findings and conclusions regarding each of these items have been summarized and are presented below. CURRENT STATE OF PRACTICE MSE walls are important infrastructure assets. However, unlike bridges and pavements, they are often overlooked. The current state of practice with respect to the management of MSE walls as assets can be characterized thusly: • There is no widely used, consistently applied system for managing MSE wall assets. • Fewer than one-quarter of state-level transportation agen- cies have developed any type of MSE wall inventory data beyond that which may be captured as part of their bridge inventories. • Still fewer agencies have the methods and/or means to support their inventories with data from ongoing inspec- tions from which assessments of wall performance can be made. • Some previously established wall inventory and inspec- tion activities have ceased because of lack of resources and funding. Regarding the inventory and gathering of MSE wall-related data once the walls are constructed and accepted, current prac- tice can be generally described as follows: • Responsibility for MSE walls after their construction usually rests with maintenance personnel operating in a decentralized structure, while most inventories are managed by a geotechnical engineer or similar person at an agency-wide level. However, in 20% of agencies, no one has end responsibility for MSE walls. • Various types of data are collected and maintained in order to assess wall performance. Most frequently, the data consist of ratings that describe the observed condi- tion of wall features. • The manner in which wall features are observed and assessed varies between agencies, as do the rating criteria themselves. • Rating criteria are usually more subjective than objective. • When scheduled, the frequency of data collection var- ies from two to 15 years, although wall performance monitoring activities are most often (i.e., two-thirds of the time) simply reactive to reported incidents of adverse performance. Once asset data have been collected, they must be assessed to predict future performance and determine maintenance and management activities. With respect to MSE walls, current practice in the area of assessment can be basically described this way: • Agencies believe that drainage, global stability, and corrosion/degradation of internal reinforcement are the most important issues affecting the long-term perfor- mance of MSE walls. • Wall performance is sometimes only one factor used in making asset-management decisions. • No state transportation agency has a specific method- ology for assessing long-term performance of existing MSE walls. • Similarly, there appears to be no specific methodology for accurately predicting the remaining service life of an MSE wall. DIRECTION OF STATE OF PRACTICE As walls have aged and adverse performance (whether age- related or not) has occurred, more agencies are becoming aware of a need for long-term performance monitoring of MSE walls. An opinion voiced by some survey respondents is that there is insufficient attention given to long-term performance of MSE walls despite the potential for poor performance of this important asset. One reason is that, while other assets such as pavements and bridge structures are subject to formal inspec- tion and reporting requirements, there are no such requirements for retaining walls, and in particular MSE walls. Without such requirements, respondents noted difficulty in obtaining fund- ing for wall inspection and management. Consequently, it appears that the direction of practice is largely limited to the status quo, with relatively few agencies performing inspections or conducting assessments. However, it is anticipated that as experience with MSE walls accumulates, those that are able to secure funding and resources will continue to develop, refine, CHAPTER SIX CONCLUSIONS

28 In summary, current effective practices for inventorying and assessing the performance of MSE walls include: • Use of inventory and assessment systems with features that are as simple to use and as objective as reasonably possible • Use of rating criteria that are specific to particular wall elements and/or conditions • Use of numeric rating scales that correspond to other scales already in use for other asset classes such as bridges • Incorporation of MSE wall inventory and assessment systems together with systems for other asset classes. Current effective practices for improving the performance of MSE walls include: • Use of pre-approval process for wall design and/or wall supplier • Provision of adequate internal and external drainage. AREAS NEEDING IMPROVEMENT AND/OR RESEARCH Today there are many millions of square meters of MSE walls with typical design lives of 75 to 100 years. The oldest of these walls are about 40 years old. Instances of MSE wall failures and poor performance are expected to increase as walls age. To better assess the performance of MSE walls, the following practices would be beneficial: • Greater recognition of MSE walls and retaining walls in general as important infrastructure assets • Increased availability of funding and other resources for inventory and assessment activities • Active involvement of a larger number of agencies in MSE wall inventory and assessment activities • Greater consistency across agencies relative to the way that inventory and assessment activities are performed • Greater use of bridge and other existing asset inventory data for MSE wall inventories. To move beyond current inventory and the data baselines now being established, repeated observations and performance predictions will be needed, as will specific decision-making methodologies. To this end, research relative to the following topics would be helpful: • Improved ability to evaluate the integrity of existing MSE reinforcement systems using methods that are economi- cally and logistically effective • Standards for performance data baselines and data col- lection activities • Predictive models for remaining MSE wall service life • Methods of risk assessment specifically for MSE walls and, more generally, for various types of retaining walls. A potential research problem statement for predictive models for remaining MSE wall service life is presented in Appen- dix D. The statement is adaptable to the other identified research needs. and better calibrate procedures regarding design, construction, condition assessment, and asset management decision making. EFFECTIVE PRACTICES Although wall inventory and monitoring practices vary between agencies, effective practices can be extracted from systems currently in use. The most well-implemented and developed wall inventory and assessment system in the United States appears to be the Wall Inventory Program developed by the FHWA for the National Park Service. The system uses “conditions narratives” (the preparation of which is illustrated by only general guidance, thus making them fairly subjective) to describe the conditions of certain wall elements, and then these narratives are converted to a numeric rating. Although the multiple steps in the rating process increase the effort required to use the system, an inherent strength is that it can be applied to many wall types (not just MSE walls). Other wall inventory and assessment systems such as those used by Pennsylvania and Nebraska are relatively simple to use and appear to be less interpretive. Such characteristics typically lead to greater consistency in data interpretation and broader use. Without consistency in collected datasets, broadly applica- ble conclusions are more difficult to reach, and methodologies developed from inconsistent data are inherently less robust. The numeric ratings associated with these two particular systems are also compatible with the 0 (worst) to 9 (best) scale already used by many in the assessment of bridges, thus facilitating the development of readily accessible MSE wall assessment tools and methods within the domain of asset management already occupied by other asset types. Other desirable practices include that reflected in the Nebraska system, in which rating criteria are specific to each element or wall condition rather than being generic. This specificity avoids vagueness and contributes to greater consis- tency. For example, a rating of 6 is assigned “when less than 25% of the wall area shows deterioration,” and a rating of 5 is assigned “when wall panels have bowed outward to where connectors between panels are visible and deforming.” This would be in contrast to a system in which a rating of 3 is assigned if “the wall exhibits ‘extensive’ distress.” The wall inventory and assessment system employed in Pennsylvania reflects another apparently effective practice, in that it actively and regularly inspects all of its retaining walls (inclusive of MSE types) and manages its inventory within the same framework as it does its bridges. In this man- ner, overlaps and gaps in inventory are minimized, and data and assessments are kept current. Although individual experiences and beliefs regarding prac- tices that improve wall performance vary, most agencies agree that the use of a pre-approved wall design and/or wall supplier helps ensure better wall performance. Similarly, based on the “most important lessons learned,” many agencies believe that providing adequate drainage, both internal and external, is an essential practice in realizing good MSE wall performance.

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Fishman, K.L. and J.L.Withiam, NCHRP Report 675: LRFD Metal Loss and Service-Life Strength Reduction Factors for Metal-Reinforced Systems, Transportation Research Board of the National Academies, Washington, D.C., 2011, 116 pp. Gerber, T.M., “Observing and Improving the Performance of Two-Stage Mechanically Stabilized Earth (MSE) Walls,” Proceedings of GeoFrontiers 2011, Dallas, Tex., Mar. 13–16, 2011, pp. 3459–3468. Gerber, T.M., J.A. Bay, and R.B. Maw, “Inspection and Observed Performance of Mechanically Stabilized Earth (MSE) Walls,” Proceedings of the 41st Symposium on Engi- neering Geology and Geotechnical Engineering, Boise, Idaho, Apr. 9–11, 2008, pp. 167–182. Hearn, G., Feasibility of Management Systems for Retaining Walls and Sound Barriers, Report Number CDOT-DTD- 200-3, Colorado Department of Transportation Research Branch, Boulder, 2003, 106 pp. Highway Innovative Technology Evaluation Center, Guide- lines for Evaluating Earth Retaining Systems, CERF Report 40334, Civil Engineering Foundation (CERF), Washing- ton, D.C., 1998, 32 pp. Holtz, R., “Reinforced Soil Technology: From Experimen- tal to the Familiar,” Terzaghi Lecture, GeoFlorida, Palm Beach, Fla., 2010. Jensen, W. and A. Arthur, Inspector’s Manual for Mechani- cally Stabilized Earth Walls, prepared for Nebraska Depart- ment of Roads, Contract Number SPR-1(09), 2009, p. 320. Koerner, R.N. and G.R. Koerner, A Database and Analysis of Geosynthetic Reinforced Wall Failures, GRI Report #38, Geosynthetic Institute, Folsom, Pa., 2009, 195 pp. Koerner, R.N. and G.R. Koerner, “Recommended Layout of Instrumentation to Monitor Potential Movement of MSE

30 Walls, Berms and Slopes,” GRI White Paper #19, Geo- synthetic Institute, Folsom, Pa., 2011, 18 pp. Lostumbo, J.M. and O. Artieres, “Geosynthetic Enabled with Fiber Optic Sensors for MSE Bridge Abutment Supporting Shallow Bridge Foundations,” Proceedings of GeoFrontiers 2011, Dallas, Tex., Mar. 13–16, 2011, pp. 3497–3504. Molla, A., City of Seattle Retaining Walls Condition Assess- ment, Unpublished, 2009, 4 p. Narsavage, P., “MSE Walls Problems and Solutions,” pre- sented at Ohio DOT Geotechnical Workshop, Columbus, Apr. 11, 2006. Nebraska Department of Roads, Inspector’s Manual for Mechanically Stabilized Earth Walls, Lincoln, 2009, 37 pp. New York State Department of Transportation, Mechanically Stabilized Earth System Inspection Manual, Geotechnical Engineering Manual 16, Albany, 2007, 95 pp. Ohio Department of Transportation, MSE Wall Inspection Checklist, Ohio Department of Transportation, Columbus, 2007, 11 pp. Passe, P.D., Mechanically Stabilized Earth Wall Inspector’s Handbook, Florida Department of Transportation, Talla- hassee, 2000, 47 pp. Peck, R.B., “Advantages and Limitations of the Observa- tional Method in Applied Soil Mechanics,” The Ninth Rankine Lecture, Geotechnique, Vol. XIX, No. 2, June 1969, pp. 169–187. Pennsylvania Department of Transportation, 2010, Bridge Safety Inspection Manual, 2nd ed., Pennsylvania Depart- ment of Transportation, Harrisburg, 2010, 482 pp. Reddy, D.V., F. Navarrete, C. Rosay, A. Cira, A.K. Ash- mawy, and M. Gunaratne, Long-term Behavior of Geo- synthetic Reinforced Mechanically Stabilized Earth (MSE) Wall Systems—Numerical/Analytical Studies, Full Scale Field Testing, and Design Software Development, Final Report, Contract No. BC-129, Florida Department of Transportation, Tallahassee, 2003, 281 pp. Stuedlein, A.W., M. Bailey, D. Lindquist, J. Sankey, and W.J. Neely, “Design and Performance of a 46-m-High MSE Wall,” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 136, No. 6, 2010, pp. 786–796. Swenson, A., Evaluation and Analysis of Utah Department of Transportation MSE Wall Performance, MS thesis, Brigham Young University, Provo, Utah, 2010. Turner, D., “A Retaining Wall Management System for ODOT Asset Management,” presented at 34th Northwest Geotechnical Engineers Workshop, Springdale, Utah, 2008. Wheeler, J.J., “New York’s Mechanically Stabilized Earth Cor- rosion Evaluation Program,” CD-ROM, 81st Annual Meet- ing of the Transportation Research Board, 2002, 21 pp.

31 APPENDIX A Survey Questionnaire

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43 SURVEY RESPONDENTS (BY INDIVIDUAL) Ahmad, Ken; Foundation Engineer; Ontario, Ministry of Trans- portation (Ontario, Canada) Annable, Jonathan; Assistant Division Head—Materials; Arkansas State Highway and Transportation Department (Arkansas) Arndorfer, Robert; Foundation and Pavement Engineering Supervisor; Wisconsin DOT (Wisconsin) Bart, Bradley; Kentucky Transportation Cabinet (Kentucky) Benda, Christopher; Soils and Foundations Engineer; Vermont Agency of Transportation (Vermont) Brennan, James; Assistant Geotechnical Engineer; Kansas DOT (Kansas) Buu, Tri; Geotechnical Engineer; Idaho Transportation Depart- ment (Idaho) Chlak, Byron; Bridge Preservation Specialist; Alberta Trans- portation (Alberta, Canada) Connors, Peter; Geotechnical Engineer; Massachusetts DOT (Massachusetts) Davis, Kaye; Geotechnical Engineer; Alabama DOT (Alabama) Dickson, Todd; Civil Engineer 2; New York State DOT Geo- technical Engineering Bureau (New York) Dusseault, Chuck; Geotechnical Section Chief; New Hamp- shire DOT (New Hampshire) Endres, Richard; Supervising Engineer of Geotechnical Ser- vices; Michigan DOT (Michigan) Falk, Mark; Assistant Chief Engineering Geologist; Wyoming DOT (Wyoming) Fisher, James; Lab Coordinator; West Virginia DOT (West Virginia) Fontaine, Leo; Transportation Principal Engineer; Connecticut DOT (Connecticut) Griese, Kevin; Geotechnical Engineer; South Dakota DOT (South Dakota) Griswell, Kathryn; Earth Retaining Systems Specialist; Cal- trans (California) Guido, Jonathan; Senior Geotechnical Engineer; Oregon DOT (Oregon) Higbee, Jim; Geotechnical Engineer; Utah DOT (Utah) Hoyt, James; Assistant Director Materials Research and Envi- ronment; New Brunswick DOT (New Brunswick, Canada) Hunter, Brian; Chemical Testing Engineer; North Carolina DOT Materials and Tests (North Carolina) Jackson, Jeff; Geotechnical Engineer; Montana DOT (Mon- tana) Ketterling, Jon; NDDOT Geotechnical Engineer; North Dakota DOT (North Dakota) Kramer, Bill; Foundations Engineer; Illinois DOT (Illinois) Krusinski, Laura; Senior Geotechnical Engineer; Maine DOT (Maine) Lawler, Ashton; State Program Manager for Geotechnical Design of Structures; Virginia DOT (Virginia) Lindemann, Mark; Soil Mechanics Engineer; Nebraska Depart- ment of Roads (Nebraska) MacAskill, Wayne; Contract Administrator; Nova Scotia Trans- portation and Infrastructure Renewal (Nova Scotia, Canada) Marcus, Galvan; State Geotechnical Engineer; Texas DOT (Texas) McLain, Kevin; Geotechnical Engineer; Missouri DOT (Missouri) Meyers, Robert; NMDOT State Geotechnical Engineer; New Mexico DOT (New Mexico) Nelson, Blake; Geotechnologies Engineer; Minnesota DOT (Minnesota) Oliver, Len; Civil Engineering Manager 2; Tennessee DOT (Tennessee) Romero, Ricardo; Acting Chief, Soils Engineering Office; Puerto Rico Highway Authority (Puerto Rico) Salazar, John; Chief Geotechnical Engineer; Nevada DOT— Materials Division∼Geotechnical Engineering Branch (Nevada) Scruggs, Thomas; State Geotechnical Engineer; Georgia DOT (Georgia) Sizemore, Jeff; Geotechnical Design Support Engineer; South Carolina DOT (South Carolina) Smadi, Malek; Supervisor, Geotechnical Operations; Indiana DOT (Indiana) Stanley, Robert; Soils Design Engineer; Iowa DOT (Iowa) Tsai, Ching; Senior Geotechnical Specialist; Louisiana Department of Transportation and Development (Louisiana) Wang, Trever; Supervising Professional Engineer; Colorado DOT (Colorado) Wetz, Norman; Geotechnical Design Engineer; Arizona DOT (Arizona) Yea, Howard; Director, Bridge Standards; Saskatchewan Ministry of Highways and Infrastructure (Saskatchewan, Canada) SURVEY RESPONDENTS (BY AGENCY LOCATION) Alabama Arizona Arkansas California Colorado Connecticut Georgia Idaho Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Massachusetts Michigan Minnesota APPENDIX B List of Survey Respondents

44 Tennessee Texas Utah Vermont Virginia West Virginia Wisconsin Wyoming Alberta, Canada New Brunswick, Canada Nova Scotia, Canada Ontario, Canada Saskatchewan, Canada Missouri Montana Nebraska Nevada New Hampshire New Mexico New York North Carolina North Dakota Oregon Puerto Rico South Carolina South Dakota

45 • “Use the right technology for the right application. For example, consider need and possibility to achieve various settlement/rigidity constraints and match service level to appropriate cost for application.” • “Providing a sound and firm foundation for support of the wall; and providing proper drainage within the wall sys- tem and adjacent to the wall geometry.” • “Performance depends on quality of construction and quality of retained backfill materials.” • “Make sure the contractor is using the specified reinforced fill material and is constructing according to plans.” • “By having a formal wall approval process we have lim- ited the use of modular block wall systems and the deterio- ration of these facing elements due to deicing chemicals.” • “The systems can last forever but must be designed and built correctly.” • “Electrochemical property requirements for backfill material were not specified for one wall built in the late 70s. As a result, the wall failed due to corrosion of the steel reinforcements when it was about 25 years old.” • “You need to have an inventory and know where all the walls are that you own.” • “For the most part, NYSDOT has had very few problems with MSE Structures. We do know that great care must be taken in constructing these structures. If you start wrong in the beginning you’ll always be seeing problems in the walls.” • “The inadequate durability of modular block MSE wall facings in locations affected by winter roadway salt application.” • “Prevent surface runoff or other external water sources from inundating reinforced zone.” • “I think we are so conservative in our designs that we have not had any problems with our long term stability of our MSE walls.” • “This is an issue which has not been addressed by the agency.” • “Lesson(s) learned—‘The outside may get ugly—it’s the inside that matters.’ We had an MSE ride a landslide downslope 32 ft back in the 1970’s. It deformed signifi- cantly, but is still in service today. We have had several lose foundation support. But as long as they were able to move and readjust the stresses through deformation, with no loss of backfill, they have all been able to stay in ser- vice, some for decades. However, excessive consolida- tion settlement and internal drainage failures have lead to issues with cavities and retainment loss. These MSE failed within months and had to be replaced. Amazing[ly] flex- ible, but only up to a limit. It’s what’s inside that counts.” • “Quality of construction. Drainage, drainage, drainage (including erosion). Corrosion of metallic reinforcement.” • “Ensure corrosion monitor readings are performed at a regu- lar inspection rate. If a failure occurs then notify appropriate subsection.” • “We don’t have a lot of MSE walls relative to other states, so this question is difficult to answer. We have not had problems that I am aware of with our MSE walls.” • “Put tight requirements on the modular blocks. Make sure the wall is well drained internally and externally.” • “So far have performed very well.” • “Proper drainage within the wall and proper external drainage behind and in front of the wall.” • “Use of fine-grained select fill has resulted in the migra- tion of material out from behind walls. We have thou- sands of square foot of wall that was backfilled with this type of material. Many walls have shown distress as a result. We have coarsened up the gradation of select fill to lessen the potential of fill migration.” • “We have had some failures and problems that have shown the need for an assessment, inventory, and inspec- tion program.” • “Drainage, drainage, drainage.” • “W-a-t-e-r: from any and all directions and sources.” • “Following proper construction procedures and follow- ing material specifications.” • “Performing and adequate geotechnical subsurface investigation.” • “Settlement.” • “Investigate and address identified problems quickly.” • “The recognition that most MSE wall problems are almost always related to a combination of deficiencies, hardly ever just one single issue. The ‘devil is always in the details,’ so to speak. It is important to keep in mind that most walls are categorized as a Series Engineering System, as opposed to a Parallel Engineering System with respect to external and global stability consider- ations. Using ‘averaged’ shear strengths along a Linear/ Series Wall System can actually cause a real stability failure within a known weak design reach . . . as the weakest link will most assuredly show up as a stability issue on any shallow wall foundation. There is typically no benefit from a redundant parallel system as in most other structure types. Also, we have learned the hard way that MSE Wall reinforcing details around obstruc- tions must be identified early-on in the design phase, as it is always a hassle to deal with during construction. And last, but certainly not the least, wall drainage is a huge component in any MSE Wall project, both during construction and throughout the lifetime of the struc- ture. In summary . . . external/global stability, internal reinforcing details and drainage should be high on any engineer’s checklist of important considerations neces- sary for the successful performance of any MSE Wall Project.” • “Freeze and thaw of block wall, surface run-off seep into the wall.” • “Improve Specifications, Approved Products List, Inspector and contractor training.” APPENDIX C “Most Signficant Lesson(s) Learned” as Reported by Agencies

46 • “None of our installations have reached an age where failure would be anticipated. To date, no significant per- formance issues have been identified.” • “[ . . . N]eed to model to predict the life of the reinforce- ment.” • “Performance of nearby drainage culverts can have signifi- cant impacts on wall performance. In our case, a collapsed culvert resulted in local groundwater table above the height of the wall. Other lessons: the bench at the base of the MSE wall is important to maintain.” • “[Our agency] has been using MSE walls for over 30 years with great success. Our only problems have been poor construction practices which are found and corrected before walls are accepted from the Contractor. We attribute our suc- cess to good geotechnical design, quality backfill required and only using pre-approved walls systems that meet AASHTO requirements.” • “To make sure the ends of the wall where the access trails to build the wall are properly compacted.” • “We have to get beyond our reactive mentality and be pro- active in monitoring these walls.”

47 PROBLEM TITLE Prediction of Remaining Service Life for Mechanically Stabi- lized Earth (MSE) Walls RESEARCH PROBLEM STATEMENT There are an estimated 16.3 million square meters of various types of walls along the nation’s highways (DiMaggio 2008), with an average of 850,000 square meters of mechanically stabi- lized earth (MSE) wall with precast facing now being built each year in the United States at a cost of $160 to $650 per square meter (Elias et al. 2004; Berg et al. 2009). However, unlike bridges and pavements, MSE walls and retaining walls in general are often overlooked as assets. While the U.S. federal government has fostered the development of the National Bridge Inventory System (NBIS) that involves inspection of the nation’s bridges every two years, there is no existing, dedicated management system addressing the whole of the nation’s retaining walls, MSE or otherwise. The long-term performance of MSE walls depends on various factors, and unfortunately there have been instances of adverse performance. Like every important class of assets, MSE walls need periodic inspection, assessment, and management. To date, some states have established MSE wall monitoring programs, while several others are looking for guidance, tools, and funding to establish their own monitoring program (Gerber 2012). During the development of NCHRP Project 20-05, Syn- thesis Topic 42-05, Assessing the Long-Term Performance of Mechanically Stabilized Earth (MSE) Walls, it was determined that less than a quarter of state-level transportation agencies in the United States have developed some type of MSE wall inventory beyond that which may be captured as part of their bridge inventories (Gerber 2012). Fewer still have the meth- ods and means to populate their inventories with data from on- going inspections from which assessments of wall performance could be made. The synthesis project determined that in order to “move beyond current inventorying activities and the data baselines now being established, repeated observations and per- formance predictions will be needed, as will rational decision- making methodologies” (Gerber 2012). To make this leap in asset management practice, research relative to the following topics is needed: • “Improved ability to evaluate the integrity of existing MSE reinforcement systems using methods that are economi- cally and logistically effective. • Standards for performance data baselines and data collec- tion activities. • Predictive models for remaining MSE wall service life. • Methods of risk assessment specifically for MSE walls and more generally for various types of retaining walls.” LITERATURE SEARCH SUMMARY As part of NCHRP Project 20-07, Task 259, Brutus and Tauber (2009), concluded that there was/is no data or methods available in technical literature for the estimation of design/service life of existing retaining walls. Based on a survey of transportation agencies, a similar conclusion was reached by Gerber (2012)—no transportation agency currently has a well-established methodol- ogy for predicting future MSE wall performance or remaining design life. Certainly some agencies are monitoring corrosion in some walls (see Fishman and Withiam 2011), but a systematic procedure for determining remaining wall life with consideration of all other parameters believed to be important to performance (such as drainage) was not identified. Additionally, methods for risk assessment for MSE walls were found to largely be absent, although nascent efforts can be found in work reported by Bern- hardt et al. (2003), Bay et al. (2009), and DeMarco et al. (2010). Consequently both methods for design life prediction and risk assessment are needed. Also needed are well-developed tools for gathering wall performance data that will be needed as input and/or calibration parameters for such methods. Again, some efforts in the area are underway (see Fishman and Withiam 2011 regarding corrosion monitoring, Lostumbo and Artieres 2011 regarding in-situ stress monitoring of reinforcement), but greater progress is needed. Recent technological advances in structural health monitoring present promising avenues of research and progress in asset management. References Bay, J.A., L.R. Anderson, T.M. Gerber, and R.B. Maw, An Inspection, Assessment, and Database of UDOT MSE Walls, Report Number UT- 09.21, Utah Department of Transporta- tion, Salt Lake City, 2009. Berg, R.R., B.R. Christopher, and N.C. Samtani, Design of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes, Volume 1, Report FHWA-NHI-10-024, Federal High- way Administration, Washington, D.C., 2009, 306 pp. Bernhardt, K.L.S., J.E. Loehr, and D. Huaco, “Asset Manage- ment Framework for Geotechnical Infrastructure,” Journal of Infrastructure Systems, Vol. 9, No. 3, 2003, pp. 107–116. Brutus, O. and G. Tauber, Guide to Asset Management of Earth Retaining Structures, prepared as part of NCHRP Project 20-07, Task 259, Transportation Research Board of the National Academies, Washington, D.C., Oct. 2009, 120 pp. DeMarco, M.J., R.J. Barrows, and S. Lewis, “NPS Retaining Wall Inventory and Assessment Program (WIP): 3,500 Walls Later,” Proceeding of Earth Retention Conference 3, Bellevue, Wash., Aug. 1–4, 2010a, pp. 870–877. DiMaggio, J.A., “Geotechnical Engineering Assets and Liabilities on Surface Transportation Facilities,” presented at National Workshop on Highway Asset Management and Data Collec- tion, Durham, N.C., Sep. 25, 2008. APPENDIX D Research Problem Statement

48 Task 3: Apply the method in order to both calibrate and verify it against case histories and/or known performance data for par- ticular groups of MSE walls. It is recognized that a rigorous assessment of the method’s predictive ability by comparison with existing wall inventories will be limited by the availability of performance data as well as the ages of walls in our existing MSE wall inventories. Task 4: Publish and disseminate results. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $XXX,XXX.XX Research Period: XX Months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION MSE walls are being constructed at an ever-increasing rate. The oldest walls in the U.S. inventory are about 40 years old, and most walls have an intended design life of 75 to 100 years. However, the age-related performance of the technology has not been fully assessed, and more instances of adverse performance are expected with time. Some agencies are now gathering per- formance data, but predictive models for remaining MSE wall service life are needed so that appropriate management and main- tenance and/or replacement decisions can be made. The initial availability of predictive tools would assist agencies in determin- ing whether and/or how much to invest in MSE wall inventory and assessment systems. By facilitating broader participation and greater consistency in methods and practice, greater improve- ments in asset management and service-life predictive models will be realized. Without the initial investment represented by this development of a remaining service life model, needed prog- ress will continue to go unrealized. Elias, V., J. Welsh, J. Warren, R. Lukas, J.G. Collin, and R.R. Berg, Ground Improvement Methods, Participant Note- book, NHI Course 132034, FHWA NHI-04-001, National Highway Institute, Federal Highway Administration, Wash- ington, D.C., 2004, 1,022 pp. Fishman, K.L. and J.L.Withiam, NCHRP Report 675: LRFD Metal Loss and Service-Life Strength Reduction Factors for Metal-Reinforced Systems, Transportation Research Board of the National Academies, Washington, D.C., 2011, 116 pp. Gerber, T.M., Assessing the Long-term Performance of Mechan- ically Stabilized Earth (MSE) Walls, NCHRP Project 20-05, Synthesis Topic 42-05, Transportation Research Board of the National Academies, Washington, D.C., 2012. Lostumbo, J.M. and O. Artieres, “Geosynthetic Enabled with Fiber Optic Sensors for MSE Bridge Abutment Supporting Shallow Bridge Foundations,” Proceedings of GeoFrontiers 2011, Dallas, Tex., Mar. 13–16, 2011, pp. 3497–3504. RESEARCH OBJECTIVE The primary objective of this research effort is to establish a meth- odology for predicting the remaining service life of MSE walls. To meet this objective, the following tasks are proposed. Task 1: Review literature for information regarding methods for predicting service life of engineered structures other than retaining walls (such as pavements and bridges). From this review, identify key parameters and/or approach concepts that can be applied to MSE walls. Also part of this task will be the collection of case history data for subsequent calibration and verification activities. Task 2: Develop an initial methodology based on the results of Task 1. While corrosion rate is anticipated to play a major role in the method, other parameters such as drainage are also anticipated to be important. It is anticipated that the method will tie wall features and performance observations to par- ticular distress mechanisms. Because of this, particular con- sideration will be given to the nature and robustness of the analytical model’s input parameters. The parameters selected for the model will influence future standards for MSE wall performance data baselines and data collection activities.

Abbreviations used without definitions in TRB publications: AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation