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Publication Number: FHWA-HRT-10-077
Date: July 2013

 

Composite Behavior of Geosynthetic Reinforced Soil Mass

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FOREWORD

Through the Federal Highway Administration’s (FHWA) Every Day Counts initiative, geosynthetic reinforced soil (GRS) was distinguished apart from traditional mechanically stabilized Earth technology. The separation is based on the reinforcement spacing, with GRS referred to as alternating layers of closely spaced (≤ 12 inches (300 mm)) geosynthetic reinforcement and a compacted granular fill material. The close reinforcement spacing increases the soil-geosynthetic interaction, leading to full composite behavior. This study investigated the composite behavior of GRS.

A major finding of this study was a new method to evaluate the required reinforcement strength based on the results of full-scale plane strain testing conducted at FHWA’s Turner-Fairbank Highway Research Center. This semi-empirical equation was subsequently selected by FHWA for inclusion in the new internal stability design method presented in the Geosynthetic Reinforced Soil Integrated Bridge System Interim Implementation Guide.(1) The methodology and testing that led to this new design equation are presented in this report, along with further documentation regarding the composite behavior of GRS and the new FHWA GRS design method.

Jorge E. Pagán-Ortiz
Director, Office of Infrastructure
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.

 

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

 

Technical Report Documentation Page

1. Report No.

FHWA-HRT-10-077

2. Government Accession No. 3 Recipient's Catalog No.

4. Title and Subtitle

Composite Behavior of Geosynthetic Reinforced Soil Mass

5. Report Date

July 2013

6. Performing Organization Code
7. Author(s)

Jonathan T.H. Wu, Thang Q. Pham, and Michael T. Adams

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

Department of Civil Engineering
University of Colorado Denver
1200 Larimer Street
Denver, CO 80217-3364

10. Work Unit No. (TRAIS)

11. Contract or Grant No.
12. Sponsoring Agency Name and Address

Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period Covered

 

14. Sponsoring Agency Code

 

15. Supplementary Notes

The FHWA Contracting Officer’s Technical Representative (COTR) was Mike Adams, HRDI-40.

16. Abstract

This study investigated the composite behavior of a geosynthetic reinforced soil (GRS) mass. Many studies have been conducted on the behavior of GRS structures; however, the interactive behavior between the soil and geosynthetic reinforcement in a GRS mass has not been fully elucidated. Current design methods consider the reinforcement in a GRS structure as tiebacks and adopt a design concept that the reinforcement strength and reinforcement spacing produce the same effects on the performance of a GRS structure. This has encouraged designers to use stronger reinforcement at a larger spacing to reduce time and effort in construction.

 

A series of large-size generic soil geosynthetic composite (GSGC) tests were designed and conducted to examine the behavior of a GRS mass under well-controlled conditions. The tests clearly demonstrated that reinforcement spacing has a much stronger impact than reinforcement strength on the performance of the GRS mass. An analytical model was established to describe the relative contribution of reinforcement strength and reinforcement spacing. Based on the analytical model, equations were developed to calculate the apparent cohesion of a GRS composite, the ultimate load-carrying capacity of a GRS mass, and the required tensile strength of reinforcement for a prescribed value of spacing. The equations were verified using measured data from the GSGC tests and measured data from large-size experiments by other researchers, as well as by results of the finite element (FE) method of analysis.

 

Due to the popularity of GRS walls with modular block facing, an analytical procedure was developed for predicting the walls’ lateral movement. This procedure also allows the required tensile strength of the reinforcement to be determined by simple calculations. In addition, compaction-induced stresses, which have usually been ignored in design and analysis of GRS structures, were investigated. An analytical model for estimating compaction-induced stresses in a GRS mass was proposed. Preliminary verification of the model was made by using results from the GSGC tests and FE analysis. The dilative behavior of a GRS composite was also examined. The presence of geosynthetic reinforcement has a tendency to suppressdilation of the surrounding soil and reduce the angle of dilation of the soil mass. The dilative behavior offers a new explanation of the reinforcing mechanism, and the angle of dilation may be used to reflect the degree of reinforcing of a GRS mass.

17. Key Words

Geosynthetic reinforced soil, GRS, Retaining walls, Analysis, Design, Composite, Compaction

18. Distribution Statement

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161.

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

211

22. Price
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

 

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

CHAPTER 1. INTRODUCTION

CHAPTER 2. LITERATURE REVIEW

CHAPTER 3. ANALYTICAL MODEL FOR CALCULATING LATERAL DISPLACEMENT OF A GRS WALL WITH MODULAR BLOCK FACING

CHAPTER 4. GSGC TESTS

CHAPTER 5. ANALYTICAL MODELS FOR EVALUATING CIS, COMPOSITE STRENGTH PROPERTIES, AND REQUIRED REINFORCEMENT STRENGTH

CHAPTER 6. FE ANALYSES

CHAPTER 7. SUMMARY AND CONCLUSIONS

REFERENCES

LIST OF FIGURES

LIST OF TABLES

 

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