Design Manual forNational Concrete Masonry Association3rd Edition5th Printing

ABOUT THIS PUBLICATIONThe Design Manual for Segmental Retaining Walls (SRW) is a publication of the National Concrete MasonryAssociation. The first edition of the Design Manual was published in 1993 and a second one in 1997. Over thelast decade, there have been significant changes in the state-of-knowledge regarding mechanically stabilized earth(MSE) and SRWs. These changes have been incorporated into the third edition of this Design Manual.The technical editors of the first edition, Michael R. Simac, P.E., Richard J. Bathurst, Ph.D., P.Eng., Ryan R. Berg,P.E. and Steven Lothspeich, P.E. and the second edition, James G. Collin, Ph.D., P.E., are greatly acknowledged fortheir contribution on establishing the methodology on past editions.The Design Manual is under the direct responsibility of the NCMA SRW and Hardscape Products Committee,NCMA SRW Technical Subcommittee and its SRW Design Manual Task Group.ACKNOWLEDGEMENTSThe primary technical editor of the third edition is recognized for his significant contribution toward the developmentof this Design Manual and the associated advancement of the state-of-the-art in SRW design and construction:Michael Bernardi, P.E. with REDI Engineering, Inc.NCMA recognizes the collaboration of Dov Leshchinsky, Ph.D. for his technical guidance on the presentdocument.NCMA acknowledges with appreciation Allan Block Corporation for their efforts on developing the internal compoundstability (ICS) analysis and modeling approach and their full scale seismic research, as well as the continuous workof the SRW Design Manual Task Group members that oversaw the completion of this publication.NCMA SRW DESIGN MANUAL TASK GROUPKaren Nelson, VERSA-LOK Retaining Wall Systems – ChairDonal J. Armstrong, Anchor Wall Systems, Inc.Michael Bernardi, REDI Engineering, Inc.Richard M. Bodie, Pavestone CompanyTimothy A. Bott, Allan Block CorporationRobert D. Bowers, Nilex, Inc.R. Lance Carter, Strata Systems, Inc.Joe Friederichs, Keystone Retaining Wall Systems, Inc.Jan E. Jansson, Soil Retention ProductsSteven E. Lothspeich, Huesker, IncCameron Roberson, Rockwood Retaining Walls, Inc.Dean B. Sandri, Anchor Wall Systems, IncBrendan Sheppard, Tensar International Corp, LLCStephen Valero, Pinnacle Design/Build Group, IncTom Zeisler, Kirchner Block & Brick, Inc.Gabriela Mariscal, Staff Laision

ABOUT NCMAThe National Concrete Masonry Association (NCMA) is an international trade association representing producersand suppliers in the concrete masonry and hardscape industry. The Association is dedicated to the advancementof manufactured concrete products through research, promotion, education, and the development of manufacturingguides, design codes and resources, testing standards, and construction practices.NCMA promotes the use of segmental retaining wall products through the development and dissemination oftechnical information. This manual was prepared by NCMA and is intended as a guide for engineers and architects.The material presented herein has been reviewed by numerous individuals from a variety of backgrounds to ensurethe enclosed information is accurate and conforms to current engineering practices. However, NCMA assumes noresponsibility for errors or omissions resulting from the use of this manual.Errata associated with this manual, if any, can be found in the Resources section of the NCMA website ( illustrations and other graphic representation published in this manual are property of NCMA unless otherwisenoted.NCMA Engineering StaffRobert D. Thomas —PresidentJason J. Thompson — Director of EngineeringDennis W. Graber — Director of Technical PublicationsNathan A. Cotton — Engineering Projects ManagerGabriela Mariscal — Geotechnical EngineerNicholas Lang —Manager, Research & Development LaboratoryGary R. Sturgeon — Technical Services EngineerCopyright 2010 National Concrete Masonry Association13750 Sunrise Valley DriveHerndon, VA 20171-4662(703) 713-1900ISBN 1-881384-02-5NCMA Publication Number TR 127BFifth printing, January, 2012This book was laid out by Resimont Products, Inc.

iiiTable of Contents TABLE OF CONTENTSSECTION 1: INTRODUCTION.11.1: Purpose and Scope of Manual.11.2: Organization of the Manual.11.3: Design Philosophy.21.4: History of Segmental Retaining Wall Use.31.5: Advantages of Segmental Retaining Walls.31.6: Summary of Changes Incorporated into 3rd Edition.4SECTION 2: SEGMENTAL RETAINING WALL COMPONENTS.72.1: Segmental Retaining Wall Units.82.1.1: Dimensions.82.1.2: Mix Design, Compressive Strength and Dimensional Tolerances.102.1.3: SRW Performance Properties. Connection Strength between Geosynthetic Reinforcement and SRW Units. Determination of Shear Strength Between SRW Units.122.2: Leveling Pads.132.3: Gravel Fill and Drainage Materials.132.4: Soils .142.4.1: Soil Classifications.152.4.2: Soil Shear Strength. Different Shear Strengths for Saturated Clays.192.4.3: Soil Properties Requried for Design of SRWs.202.5: Geosynthetic Reinforcement. 222.5.1: Reinforcement Concepts.232.5.2: Long-Term Design Strength. Determination of the Long-Term Design Strength of the Geosynthetic.242.5.3: Soil-Reinforcement Interaction Performance. Coefficient of Interaction for Pullout. Coefficient of Direct Sliding.26SECTION 3: ROLES AND RESPONSIBILITIES ON PROJECTS INVOLVING SRWS.273.1: Overview of Roles. 273.2: Site Civil Engineer Suggested Roles Overview. 293.3: Geotechnical Engineer Suggested Roles Overview. 303.4: SRW Design Engineer Suggested Roles Overview. 313.5: Construction Observation and Testing Suggested Roles Overview. 32SECTION 4: WALL LAYOUT AND PLANNING.334.1: Wall Layout Example.334.2: Site, Grading, and Utility Plans.344.2.1: Location of Retaining Walls.344.2.2: Property Lines and Other Space Limitations.34

iv Design Manual for Segmental Retaining Walls 3rd Edition4.2.3: Utilities.364.2.4: Contour Lines. 374.2.5: Loading Features.374.2.6: Miscellaneous Features.374.2.7: Scale.384.2.8: Additional Information. 384.3: Retaining Wall Layout.384.4: Design.38SECTION 5: SEGMENTAL RETAINING WALL DESIGN OVERVIEW.435.1: Conventional SRW Concepts.445.2: Reinforced SRW Concepts.445.3: Potential Failure Modes for Segmental Retaining Walls.445.3.1: External Stability.465.3.2: Internal Stability.465.3.3: Facing Stability.465.3.4: Internal Compound Stability. 465.3.5: Geotechnical Concerns.475.4: Earth Pressure and Forces.495.4.1: Active Earth Pressure Coefficient.515.4.2: Failure Surface Orientation, α.515.4.3: Interface Friction Angle, δ.525.4.4: Horizontal and Vertical Components. 525.5: Design Height and Embedment.535.5.1: Design Height for SRWs.535.5.2: Embedment Requirements.535.6: Top of Wall Conditions.545.6.1: Infinite Slopes.545.6.2: Broken Backslopes.545.6.3: Surcharge Loading.555.6.3.1: Live and Dead Loads.555.6.3.2: Modeling as Uniform.555.6.3.3: Offset Surcharges.555.6.3.4: Line Loads or Point Loads.565.6.3.5: Tiers as Surcharges.565.7: Water and Drainage.565.8: Seismic Analysis.