Practices for Local Calibration of LRFD Geotechnical Resistance Factors (2023)

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2023 Practices for Local Calibration of LRFD Geotechnical Resistance Factors A Synthesis of Highway Practice Andrew Boeckmann J. Erik Loehr Dan Brown and Associates Columbia, MO Research sponsored by the American Association of State Highway and Transportation Ofcials in cooperation with the Federal Highway Administration Subscriber Categories Bridges and Other Structures • Geotechnology • Highways N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP SYNTHESIS 601

Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet by going to https://www.mytrb.org/MyTRB/Store/default.aspx Printed in the United States of America NCHRP SYNTHESIS 601 Project 20-05, Topic 53-06 ISSN 0547-5570 ISBN 978-0-309-69846-7 Library of Congress Control Number 2023934853 © 2023 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and the graphical logo are trade- marks of the National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, APTA, FAA, FHWA, FTA, GHSA, or NHTSA endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. Cover photo caption: The photograph shows a drilled shaft lateral load test for Missouri DOT research that was used to develop Missouri DOT’s agency-specific drilled shaft design provisions. NOTICE The report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the National Academies of Sciences, Engineering, and Medicine. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors. The Transportation Research Board does not develop, issue, or publish standards or spec- ifications. The Transportation Research Board manages applied research projects which provide the scientific foundation that may be used by Transportation Research Board sponsors, industry associations, or other organizations as the basis for revised practices, procedures, or specifications. The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names or logos appear herein solely because they are considered essential to the object of the report. NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transporta- tion results in increasingly complex problems of wide interest to high- way authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 ini- tiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration (FHWA), United States Department of Transportation, under Agree- ment No. 693JJ31950003. The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRB’s recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many reasons: TRB maintains an extensive com- mittee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, univer- sities, and industry; TRB’s relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of special- ists in highway transportation matters to bring the findings of research directly to those in a position to use them. The program is developed on the basis of research needs iden- tified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the FHWA. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&I’s recommendations are proposed to the AASHTO Board of Direc- tors and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement, rather than to substitute for or duplicate, other highway research programs.

e National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. e National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. John L. Anderson is president. e National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. e three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. e National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.nationalacademies.org. e Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. e mission of the Transportation Research Board is to provide leadership in transportation improvements and innovation through trusted, timely, impartial, and evidence-based information exchange, research, and advice regarding all modes of transportation. e Board’s varied activities annually engage about 8,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. e program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.

CRP STAFF FOR NCHRP SYNTHESIS 601 Christopher J. Hedges, Director, Cooperative Research Programs Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program Jo Allen Gause, Senior Program Officer Emi Carbray, Program Coordinator Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications NCHRP PROJECT 20-05 PANEL Joyce N. Taylor, Maine Department of Transportation, Augusta, ME (Chair) Melissa Batula, Pennsylvania Department of Transportation, Harrisburg, PA Anita K. Bush, Nevada Department of Transportation, Carson City, NV Joseph D. Crabtree, Kentucky Transportation Center, Lexington, KY Allison R. Hardt, Maryland Department of Transportation, Baltimore, MD Mostafa Jamshidi, Nebraska Department of Transportation, Lincoln, NE Cynthia L. Jones, Ohio Department of Transportation, Columbus, OH Jessie X. Jones, Arkansas Department of Transportation, Little Rock, AR Brenda Moore, North Carolina Department of Transportation (retired), Cary, NC Randall R. Park, Avenue Consultants, Taylorsville, UT Brian Worrel, Iowa Department of Transportation, Ames, IA Jack D. Jernigan, FHWA Liaison Jim T. McDonnell, AASHTO Liaison Stephen F. Maher, TRB Liaison TOPIC 53-06 PANEL Peter Connors, Massachusetts Department of Transportation, Boston, MA Kaye Chancellor Davis, Alabama Department of Transportation, Montgomery, AL Alexander Berndt Charlton Dettloff, Ohio Department of Transportation, Columbus, OH Ronaldo Luna, Saint Louis University, St. Louis, MO Beverly Miller, Pennsylvania Department of Transportation, Harrisburg, PA Yunxin (Jason) Qiu, Washington State Department of Transportation, Tumwater, WA Derrick David Dasenbrock, FHWA Liaison Nancy M. Whiting, TRB Liaison C O O P E R A T I V E R E S E A R C H P R O G R A M S

ABOUT THE NCHRP SYNTHESIS PROGRAM Highway administrators, engineers, and researchers often face problems for which information already exists, either in documented form or as undocumented experience and practice. This infor- mation 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 alleviating 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 evalu ating such useful information and to make it available to the entire highway community, the American Association of State High- way 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 Project 20-05, “Synthesis of Information Related to Highway Practices,” searches out and synthesizes 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. FOREWORD By Jo Allen Gause Staff Officer Transportation Research Board The AASHTO LRFD Bridge Design Specifications include provisions for geotechnical design that allow state departments of transportation (DOTs) to develop their own design methods and resistance factors. Such provisions, commonly termed “local” or “regional” and referred to in this report as “agency-specific,” are an opportunity for state DOTs to develop methods that reflect regional geology and local design and construction practices. Potential benefits of agency-specific methods include cost savings resulting from greater resistance factors associated with reduced variability and uncertainty compared with using national methods. The objective of this synthesis is to document the extent to which state DOTs have developed agency- specific geotechnical design methods and resistance factors and to also document the challenges and benefits of developing and implementing these methods. Information for this study was gathered through a literature review, a survey of state DOTs, and follow-up interviews with selected DOTs. Four case examples provide additional information on the use of agency-specific methods. Andrew Boeckmann and J. Erik Loehr, Dan Brown and Associates, collected and synthesized the information and wrote the report. The members of the topic panel are acknowledged on page iv. This synthesis is an immediately useful document that records 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.

AUTHOR ACKNOWLEDGMENTS Benjamin Rivers from the Federal Highway Administration was instrumental in assembling the survey contact list and personally requesting individual agency responses. The survey would not have achieved a high rate of response without his participation, which the authors greatly appreciate. Each of the case example agency representatives graciously donated considerable amounts of time and information during the discussion, review, and retrieval of agency records. They are • Rodrigo Herrera and Larry Jones, Florida DOT • Jesse Rauser, Louisiana DOTD • Lydia Brownell, Bryan Hartnagel, and Darren Kemna, Missouri DOT • Alexander Dettloff and Chris Merklin, Ohio DOT

Note: Photographs, figures, and tables in this report may have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at nap.nationalacademies.org) retains the color versions. 1 Summary 5 Chapter 1 Introduction 5 Objectives 6 Methodology and Outline 7 Chapter 2 Literature Review 7 History of LRFD for Geotechnical Design 10 Published Examples of Agency-Specific Geotechnical Design Methods 12 Summary of Significant Findings 13 Chapter 3 Survey Results 13 Experience with Development of Agency-Specific Methods 15 Motivations for Following AASHTO LRFD Specifications for All Geotechnical Elements 18 Motivations for Implementing Agency-Specific Methods 19 Benefits and Challenges Associated with Implementation of Agency-Specific Methods 20 Details of Agency-Specific Design Methods 24 Details of Development of Agency-Specific Provisions 31 Design Conditions for Which State DOTs Would Like to Develop Agency-Specific Methods 32 Databases of Geotechnical Information 32 Summary of Significant Findings 36 Chapter 4 Case Examples 36 Florida Department of Transportation 41 Louisiana Department of Transportation and Development 43 Missouri Department of Transportation 46 Ohio Department of Transportation 48 Lessons Learned from All Case Examples 49 Chapter 5 Summary of Findings 49 Summary of Major Findings 50 Information Gaps and Suggestions for Future Research 51 References and Additional Documents 51 References 53 Documents 54 Appendix A Survey Questionnaire 66 Appendix B Survey Responses C O N T E N T S