And Multi-Tier Mechanically Stabilized Earth Walls
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Technical Report Documentation Page 1. Report No. 2. Government 3. Recipient’s Catalog No. FHWA/TX-05/0-4485-1 Accession No. 4. Title and Subtitle 5. Report Date An Examination of Design Procedures for Single- and Multi- October 2004 Tier Mechanically Stabilized Earth Walls 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Wade N. Osborne and Stephen G. Wright 0-4485-1 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Center for Transportation Research 11. Contract or Grant No. The University of Texas at Austin 0-4485 3208 Red River, Suite 200 Austin, TX 78705-2650 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Texas Department of Transportation Technical Report 8/02 - 8/04 Research and Technology Implementation Office 14. Sponsoring Agency Code P.O. Box 5080 Austin, TX 78763-5080 15. Supplementary Notes Project performed in cooperation with the Texas Department of Transportation and the Federal Highway Administration. 16. Abstract Current AASHTO and FHWA design guidelines for MSE walls are with particular emphasis on multi-tiered wall systems. Current software including the MSEW 2.0 design software and the general-purpose slope stability software known as UTEXAS4 are also examined with emphasis placed on multi-tiered wall systems. Assumptions, differences, and issues with the present guidelines and software are identified. The impact of the assumptions and differences is examined through analyses of a number of hypothetical and actual single and multi-tiered MSE walls. Deficiencies and ambiguities in the current procedures for design of multi-tiered walls are identified and recommendations are provided. 17. Key Words 18. Distribution Statement Mechanically stabilized earth walls, Retaining walls, No restrictions. This document is available to the Slope stability, Geotechnical engineering, Soil public through the National Technical Information reinforcement Service, Springfield, Virginia 22161; www.ntis.gov. 19. Security Classif. (of report) 20. Security Classif. (of this page) 21. No. of pages 22. Price Unclassified Unclassified 202 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized An Examination of Design Procedures for Single- and Multi- Tier Mechanically Stabilized Earth Walls Wade N. Osborne Stephen G. Wright CTR Research Report: 0-4485-1 Report Date: October 2004 Research Project: 0-4485 Research Project Title Design Methodology for Tiered MSE or Concrete Block Retaining Walls Sponsoring Agency: Texas Department of Transportation Performing Agency: Center for Transportation Research at The University of Texas at Austin Project performed in cooperation with the Federal Highway Administration and the Texas Department of Transportation. Center for Transportation Research The University of Texas at Austin 3208 Red River Austin, TX 78705 www.utexas.edu/research/ctr Copyright (c) 2005 Center for Transportation Research The University of Texas at Austin All rights reserved Printed in the United States of America iv Disclaimers Author's Disclaimer: The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official view or policies of the Federal Highway Administration or the Texas Department of Transportation (TxDOT). This report does not constitute a standard, specification, or regulation. Patent Disclaimer: There was no invention or discovery conceived or first actually reduced to practice in the course of or under this contract, including any art, method, process, machine manufacture, design or composition of matter, or any new useful improvement thereof, or any variety of plant, which is or may be patentable under the patent laws of the United States of America or any foreign country. Notice: The United States Government and the State of Texas do not endorse products or manufacturers. If trade or manufacturers' names appear herein, it is solely because they are considered essential to the object of this report. Engineering Disclaimer NOT INTENDED FOR CONSTRUCTION, BIDDING, OR PERMIT PURPOSES. Project Engineer: Mark McClelland Stephen G. Wright, P.E. (Texas No. 49007) v Acknowledgments The authors express appreciation to TxDOT for their support of this research study. We are particularly grateful for the vision, guidance, constructive criticism, and continued encouragement of Mr. Mark McClelland and Mr. John Delphia of TxDOT. Mr. Marcus Galvin was also helpful in procuring the design information for a number of the MSE walls that TxDOT has constructed. vi Table of Contents 1 Introduction....................................................................................................... 1 2 Current Design Practices for MSE Walls ......................................................... 3 2.1 Introduction......................................................................................................................3 2.2 Design Guidelines............................................................................................................3 2.3 External Stability .............................................................................................................4 2.3.1 Sliding Stability...................................................................................................... 5 2.3.1.1 FHWA Method to Evaluate Sliding.................................................................... 5 2.3.1.2 AASHTO Method to Evaluate Sliding ............................................................... 6 2.3.2 Factor of Safety Against Bearing Capacity Failure ................................................ 7 2.3.3 Safety Against Overturning .................................................................................. 10 2.4 Internal Stability.............................................................................................................11 2.4.1 Rupture of Reinforcement..................................................................................... 11 2.4.1.1 Reinforcement Rupture Strength...................................................................... 11 2.4.1.2 Maximum Reinforcement Tension (TMAX)....................................................... 13 2.4.1.3 Calculation of Safety against Rupture .............................................................. 14 2.4.2 Pullout of Reinforcement...................................................................................... 17 2.4.2.1 Reinforcement Pullout Resistance (Pr) ............................................................. 17 2.4.2.2 Calculation of Safety against Pullout................................................................ 18 2.5 Global Stability..............................................................................................................19 2.5.1 FHWA and AASHTO Requirements.................................................................... 20 2.5.2 Procedure of Slices ............................................................................................... 20 2.5.3 Defining Factors of Safety.................................................................................... 21 2.5.3.1 Factor of Safety on Soil Shear Strength............................................................ 21 2.5.3.2 Balanced Factor of Safety................................................................................. 21 2.5.3.3 Factor of Safety on Reinforcement Force......................................................... 22 2.5.4 Discussion............................................................................................................. 22 2.5.5 Recommendations................................................................................................. 22 2.6 Summary........................................................................................................................23 3 Issues with Design of MSE Walls .................................................................. 25 3.1 Introduction....................................................................................................................25 3.2 Uniform Surcharge Loads..............................................................................................25 3.2.1 Effect of Uniform Surcharge Loads on the External Stability.............................. 26 3.2.2 Effect of Uniform Surcharge Loads on the Internal Stability............................... 26 3.2.3 Effect of Uniform Surcharge Loads on the Global Stability ................................ 26 3.3 Embedment of the MSE Wall........................................................................................27 3.4 Force Distribution in Reinforcement .............................................................................27 3.4.1 Internal Stability Analyses.................................................................................... 28 3.4.2 Global Stability Analyses ..................................................................................... 28 3.4.2.1 Generalized Distribution of Force in the Reinforcement.................................. 28 3.4.2.2 General-Purpose Slope Stability Software........................................................ 30 3.4.2.3 The MSEW 2.0 Software.................................................................................. 30 vii 3.5 Contribution of Reinforcement when Slip Surface Exits Wall Face at a Reinforcement Layer 31 3.6 Shape of the Slip Surfaces