TECHNICALEVALUATION

REPORT

EVALUATION OF THEMACCAFERRI TERRAMESH SYSTEM

RETAINING WALL

Prepared by theHighway Innovative TechnologyEvaluation Center (HITEC),a CERF/IIEC Innovation Center

CERF/IIEC Report: #40626June 2002

CERF/IIEC through a cooperative agreement with the Federal Highway Adminis-tration (FHWA), created the Highway Innovative Technology Evaluation Center(HITEC) to expedite the introduction of innovative products into the U.S. highwayand bridge markets.

HITEC evaluates products for which there are no recognized standards orspecifications. By providing impartial evaluations of technologies, HITEC hopesto encourage state and local governments to implement more quickly innovativeproducts in the highway system, thereby enhancing the incentives for privateindustry to invest in highway-oriented research and development. HITEC wasorganized not only to provide a service to specific clients, but also to serve as aclearinghouse for information useful to the highway community at large,particularly public sector officials.

To guide the overall process, HITEC assembles a unique, multi-disciplinary panelof experts for each evaluation. The panel works with the manufacturer of theinnovative product or technology to devise a plan for comprehensively evaluatingthe performance of the product. The panelists selected to direct the evaluationinclude experts from county, state, and federal transportation agencies, academia,and the private sector.

The information found in this report is neither an endorsement nor an approvalof a technology. Instead, the information is intended to provide the reader withaccurate information and/or a credible analysis. Also, where appropriate, HITEChopes to feed the development of national standards for innovative technologiesthrough its published reports.

If you would like further information on HITEC, please contact us at 202-785-6420, hitec@cerf.org, or visit www.cerf.org/hitec.

Cover Photos:Left: Installation of geotextile in the facing section of the wallCenter: Terramesh System wall 5 m highRight: Photos of a drainage pipe installed in the wall

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The Highway Innovative Technology Evaluation Center (HITEC), an innovation center of CERF/IIEC, serves as a clearinghouse for implementinghighway innovation by conducting nationally-focused, collaborative evaluations of new products and technologies. This report, Evaluation of theMaccaferri Terramesh System Retaining Wall, was prepared as part of the HITEC evaluation for earth retaining systems (ERS). This evaluation wasperformed on the Terramesh Retaining Wall System, a mechanically stabilized earth (MSE) structure developed, designed, and supplied by Maccaferri,Inc.

This report describes a HITEC evaluation designed to determine the basic capabilities and limitations of the Terramesh System for use as a technically-viable MSE retaining wall system. The evaluation was conducted based on material, design, construction, performance, and quality assuranceinformation outlined in the HITEC Protocol.

The Terramesh System features a Gabion basket facing of various configurations and metal double twisted grid type of soil reinforcement, which ismanufactured integrally with the basket facing blocks.

Library of Congress Cataloguing-in-Publication Data

Highway Innovative Technology Evaluation Center (U.S.)Evaluation of the Maccaferri Terramesh system retaining wall / prepared by the Highway Innovative Technology Evaluation Center (HITEC),a service center of the Civil Engineering Research Foundation (CERF).

p.cm -- (Technical evaluation report) (CERF report ; ...)Includes bibliographical references and index.ISBN 0-7844-0626-X1. Retaining walls—Evaluation. I. Title. II. Series. III. Series: CERF report ; ...

TA770 .H54 2002624.1’64—dc21

2002025574

The material presented in this publication has been prepared in accordance with generally recognized engineering principles and practices,and is for general information only. This information should not be used without first securing competent advice with respect to its suitabilityfor any general or specific application. The contents of this publication are not intended to be and should not be construed to be a standard ofthe American Society of Civil Engineers (ASCE), or its research affiliate, CERF/IIEC, and are not intended for use as a reference in purchasespecifications, contracts, regulations, statutes, or any other legal document. No reference made in this publication to any specific method,product, process, or service constitutes or implies an endorsement, recommendation, or warranty thereof by ASCE and CERF/IIEC.

ASCE and CERF/IIEC make no representation or warranty of any kind, whether expressed or implied, concerning the accuracy, completeness,suitability, or utility of any information, apparatus, product, or process discussed in this publication, and assumes no liability thereof. Anyoneutilizing this information assumes all liability arising from such use, including, but not limited to infringement of any patent or patents.

Photocopies. Authorization to photocopy material for internal or personal use under circumstances not falling within the fair use provisionsof the Copyright Act is granted by ASCE to libraries and other users registered with the Copyright Clearance Center (CCC) TransactionalReporting Service, provided that the base fee of $4.00 per article plus $.50 per page is paid directly to CCC, 222 Rosewood Drive, Danvers, MA01923. The identification for ASCE Books is 0-7844-0626-X/02. $4.00 + $.50 per page. Requests for special permission or bulk copyingshould be addressed to Permissions & Copyright Dept., ASCE.

Copyright ©2002 by the American Society of Civil Engineers.All Rights Reserved.Library of Congress Catalog Card No: 2002025574ISBN 0-7844-0626-XManufactured in the United States of America.

Abstract

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Disclaimer

This document is based on work supported by the Federal Highway Administration under Cooperative Agreement No. DTFH61-93-X-00011.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the Highway Innovative Technology EvaluationCenter (HITEC) and do not necessarily reflect the view of the Federal Highway Administration.

This report is the result of an impartial, consensus-based approach to evaluating innovative highway technology in accordance with the HITECTechnical Protocol. The data presented are believed accurate and the analyses credible. The statements made and conclusions drawn regardingthe product evaluated do not, however, amount to an endorsement or approval of the product in general or for any particular application.

v

Preface vii

Acknowledgments viii

Technical Evaluation Panel Key Contacts ix

Executive Summary x

1 Introduction 11.1 Purpose, Scope, and Basis for Evaluation 11.2 Documents Reviewed 2

2 History and System Concept 3

3 Design Method Evaluations 53.1 Performance Criteria 53.2 External Stability 5

3.2.1 Global Stability3.3 Internal Stability 6

3.3.1 Interaction Coefficient3.3.2 Corrosion/Degradation3.3.3 Allowable Strength of Reinforcement3.3.4 Connection to Facing3.3.5 Backfill in Reinforced Zone

3.4 Design Computations 83.5 Limitations 93.6 Design Details 9

3.6.1. Facing3.6.2 Wall Elements3.6.3 Barriers, Copings and Connection Appurtenances3.6.4 Obstruction Avoidance Details

4 Construction Specifications 114.1 Description 114.2 Materials 12

4.2.1 Facing Baskets4.2.2 Ring Fasteners

Contents

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4.2.3 Facing Infill Rock4.2.4 Soil Reinforcements4.2.5 Select Granular Material

4.3 Construction

5 Quality Assurance/Quality Control Systems 135.1 Galvanization 135.2 PVC Supply 135.3 Terramesh PVC Coating and Manufacture 145.4 Ring Fasteners 145.5 Construction and Quality Control Manual (Installation Manual) 145.6 Design QA/QC5.7 Warranties and Insurance

6 Performance Review 156.1 Costs 15

References 17

Appendices 19

vii

Preface

When a manufacturer is introducing a new or innovative technology to the highway community, it is often necessary to demonstratethe product to many, if not all, state highway agencies to prove that it performs as claimed. This practice is inefficient, time consuming,and often costly. To overcome these barriers, the Highway Innovative Technology Evaluation Center (HITEC) was established in 1994in cooperation with the Federal Highway Administration (FHWA), the American Association of State Highway and TransportationOfficials (AASHTO), and the Transportation Research Board (TRB). HITEC’s mission is to accelerate the process of introducingtechnological advances to the highway community.

HITEC facilitates the conduct of consensus-based, nationally accepted performance evaluations of new or innovative technologies forthe highway community. HITEC is available to evaluate products, systems, services, materials, equipment, or other technologies thatthe owners believe can be used beneficially on the nation’s highways.

The HITEC earth retaining system (ERS) program was initiated at the request of federal and state highway officials and was establishedthrough a collaborative relationship with FHWA. It is an ongoing program to evaluate the performance of proprietary ERS technologiesagainst a common evaluation plan. It is believed that the development of up-to-date evaluation criteria and performance informationwill help reduce the time and efforts required of suppliers and user agencies, and eliminate the inefficiency associated with the currentagency-by-agency approval process. The figure below illustrates the step-by-step group evaluation process pioneered by HITEC andused for this ERS program.

The fundamental feature of this process is the formation of the Technical Evaluation Panel (Panel), a group of key representativesfrom the user community, academia, and the private sector. The Panel, with the cooperation and assistance of the ERS technologysuppliers, identified the specific performance issues and concerns requiring resolution for these products to be adopted by thehighway community. The Panel oversaw the development and execution of the evaluation plan, and ultimately, reviewed the evaluationfindings.

As a result of their participation in this ERS program, many system suppliers have taken advantage of the process to modify andimprove their retaining wall systems so they conform to HITEC Protocol and AASHTO design methods. Consequently, it is importantto verify that the retaining wall system currently provided by a supplier is the same as that evaluated in this program.

HITEC is accepting applications for this ERS program on an ongoing basis and will publish the results of each evaluation. Evaluationreports will be developed to provide an analysis of each of the technologies participating in this program. Currently, there are severalreports completed and/or scheduled for publication. Additionally, HITEC created the Guidelines for Evaluating Earth RetainingSystems report (#40334), which fully describes the scope and details of the program. These reports are available from ASCE at 800-548-2723 or marketing@asce.org. Copies can also be downloaded from the web site at www.cerf.org.

1. EvaluationPanel of Public &Private SectorVolunteersFormed

3. ApplicationsSubmitted fromOwners of theTechnology

2. EvaluationPlan Developed

4. Refine PlanIf Needed &Execute Plan

5. ReportPrepared &DistributedWorldwide

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Acknowledgments

The Highway Innovative Technology Evaluation Center (HITEC), a service center of CERF/IIEC, prepared this report and wishes toacknowledge the contributions of individuals whose efforts and suggestions have significantly influenced the content of this report.

Most notably, this report is based on work and guidance by members of a technical evaluation panel who volunteered to develop theevaluation plan for this project and carry out its objectives. The HITEC Panel is composed of Chairman Terry Shike, David Evans &Associates, Inc.; Tony Allen, Washington State Department of Transportation; Randy Cannon, South Carolina Department ofTransportation; Todd Dickson, New York State Department of Transportation; Jerry DiMaggio, Federal Highway Administration; ChrisDumas, Federal Highway Administration; David Dundas, Ontario Ministry of Transportation; Dov Leshchinsky, University of Delaware;and Mark McClelland, Texas Department of Transportation. Additionally, D'Appolonia served as the consultant to the Panel and wasinstrumental in producing this report.

CERF/IIEC also wishes to thank the employees of Maccaferri, Inc. for their cooperation during the evaluation process.

Among the staff that worked on this project, I wish to acknowledge the efforts of Scott C. Edwards, Nicole Testa, and Kanako Beringerwho prepared this report for publication.

Publication of this report is made possible in part through the contributions by members of CERF's New Century Partnership:

n Black & Veatchn CH2M Hill Ltd.n Charles Pankow Buildersn Charles J. Pankow Matching Grantn Kenneth A. Roe Memorial Programn Lester B. Knight & Associatesn Parsons Brinckerhoff, Inc.n The Turner Corporation

Harvey M. BernsteinPresident & CEO, CERF/IIEC

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Technical Evaluation Panel Key Contacts

Product: Maccaferri Terramesh® System

Chair: Terry J. ShikeSenior Bridge EngineerDavid Evans & Associates, Inc.

Panelists: Tony M. AllenState Geotechnical EngineerWashington State Department of Transportation

Randy CannonBridge Design EngineerSouth Carolina Department of Transportation

Todd H. DicksonCivil Engineer IINew York State Department of Transportation

Jerry A. DiMaggioSenior Geotechnical EngineerFederal Highway Administration

Chris DumasGeotechnical EngineerEastern Resource CenterFederal Highway Administration

David Dundas, P. Eng.Senior Foundation EngineerMinistry of Transportation, Ontario

Dov Leshchinsky, Ph.D.Professor of Civil EngineeringUniversity of Delaware

Mark McClellandGeotechnical Branch ManagerTexas Department of Transportation

HITEC ProjectManager: Scott C. Edwards

Consultants: D’AppoloniaBarry ChristopherVictor EliasJames Withiam

Client: Maccaferri, Inc.10303 Governor Lane Blvd.Williamsport, MD 21795-3116Phone: 301-223-6910Fax: 301-223-6134Web: www.maccaferri-usa.comEmail: magaec@aol.com

x

Executive Summary

This evaluation was performed on the Terramesh Retaining Wall System (Terramesh System), a Mechanically Stabilized Earth (MSE)structure developed and supplied by Maccaferri, Inc. (Maccaferri) of Williamsport, Maryland. Maccaferri is part of the worldwideMaccaferri Industrial Group headquartered in Italy.

The evaluation was conducted based on design, construction, performance and quality assurance information provided by Maccaferri,the developer and supplier. This information was evaluated for conformance with the state-of-practice criteria as outlined in theHITEC Protocol. To date (2001), 37 structures have been constructed in the United States, and many more worldwide, using thissystem.

As shown in Figures 1, 2 and 3, the Terramesh System is fabricated from a double twisted steel mesh, which is galvanized andsubsequently PVC coated, and features a Gabion-type basket facing section. The facing basket is integrally manufactured with thedouble twisted wire-mesh soil reinforcement. The facing section of the unit is formed by connecting the back panel and a diaphragmto the main unit that forms rectangular-shaped cells used for infill facing stone confinement. Terramesh System units are manufacturedwith all components mechanically connected at the production facility.

Figure 1. Hexagonal Double Twisted Wire Mesh

Figure 2. Spenax Fastener

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Figure 3. Terramesh System Unit

Maccaferri introduced the system in the early 1990’s as a combination of box Gabions with a field-connected metallic mesh panel asreinforcement. That system evolved in the present system, which is fabricated of one continuous piece of woven mesh.

The design of this type of structure is fully governed by Article 5.8 of AASHTO (2000a). The design methods submitted for externaland internal stability are in accordance with the requirements for extensible reinforcements that are in AASHTO (2000a) except forany variations noted in the evaluation.

With respect to the submitted system-specific design parameters, the following are noted:

n The normalized friction coefficient F* varies widely, primarily as a function of maximum grain size and grain size distribution,within the backfill gradations permitted and commonly used for MSE structures. For construction with fine-grained backfillmeeting the current MSE specifications, an F* of 0.30 at the surface decreasing to 0.16 at a depth of 6 m (20 ft) is indicatedby current testing results. For coarse gravelly backfill, the F* is considerably higher.

n The durability of the PVC coating for in-ground use has been extrapolated from heat aging tests results based on UL 746B(Underwriters Laboratories) standard as no current ASTM or AASHTO standards are available. The acceptance criteriaoutlined in UL 746B (useful life determination) was modified for this determination, and is less restrictive. The PVC wastested in isolation, unstressed and for a shorter period of time than recommended under the UL standard. On this basis, auseful life of approximately 69 years has been established.

n The durability of the PVC coating at the face of the gabion basket exposed to UV radiation for 75 years has not beendemonstrated. It must be noted that no ASTM or AASHTO test methods are currently available for this determination. Fieldexamination of a few old existing structures suggests a useful life in excess of 45 years.

n The long-term (i.e., 75 year) strength of the Terramesh soil reinforcement, considering construction damage and allapplicable in-ground degradation/corrosion losses, has been established at 26 kN/m (1780 lb/ft). No assessment for 100-year life has been provided.

xii

n Where the vertical spacing of reinforcements for the modular Terramesh system is 0.91 m (3 ft), it is in excess of themaximum vertical spacing of 0.80 m (2.62 ft) required by AASHTO (2000a).

The construction material and methods specification and QA/QC programs submitted are in substantial agreement with currentpractice and AASHTO (2000a). Maccaferri, Inc. provides quality control for the manufactured materials in accordance with their QA/QC program. They rely on the owner’s engineers or consultants for design and construction verification and/or inspection.

The maximum height of the Terramesh System is a function of the gabion basket height, which controls vertical spacing of reinforcementsand the tensile capacity of the reinforcements. Accordingly, the maximum height for a structure statically loaded with a horizontalbackslope is on the order of 10 m (33 ft), using the standard material elements. The tallest structure completed to date in the UnitedStates is about 12-m (40-ft) high.

The Terramesh System is a technically viable MSE retaining wall system. Insufficient actual project cost data have been provided tocompare with other available MSE systems.

Introduction 1

CHAPTER 1

Introduction

12 m high wall Terramesh System installed in aresidential area

1.1 Purpose, Scope and Basis for Evaluation

This evaluation was conducted for the Terramesh Retaining Wall System developed and supplied by Maccaferri, Inc. (Maccaferri),Williamsport, Maryland. The essential elements of this mechanically stabilized earth wall (MSE) system are a Gabion basket facings,a double-twisted, galvanized and subsequently PVC coated metallic grid-type soil reinforcing elements, and a select granular backfill.Figure 3 in the Executive Summary shows front and rear isometric views of the Terramesh System.

The evaluation was conducted using material, design, construction, performance, and quality assurance information provided byMaccaferri, and was evaluated for conformance with the latest state-of-the-practice criteria as outlined in the HITEC Protocol (Protocol).The Protocol substantially incorporates the AASHTO Standard Specifications for Highway Bridges (AASHTO 2000a) and DemonstrationProject 82, FHWA-SA-96-071, (Elias and Christopher, 1996) referred to as Demo 82. Where no applicable criteria in the referenceddocuments exist, evaluations were based on state-of-the-practice as indicated in the technical literature or documentation providedby the developers.

This evaluation is intended for readers who have a working knowledge of the design and construction specification requirements inAASHTO (2000a), Article 5.8 for MSE Walls and FHWA-SA-96-071, Demo 82. Understanding the test methods and interpretingprocedures in the Appendices of FHWA-SA-96-071 is essential to understanding the test data submitted by Maccaferri in support ofproduct-specific design parameters.

The submittal by Maccaferri for the Terramesh System was evaluated relative to the Protocol developed by the HITEC Panel and theConsultant. The Protocol (see Appendix A) was further reviewed and commented by industry in a public forum prior to beingfinalized.

The results of this evaluation do not constitute an approval or a rejection of the system and/or its components. Further, anyrecommendations for modifications and/or conformance to specific evaluation criteria should not be construed as mandatory. Thepotential effects are noted, and each approval agency must determine its own requirements for implementation.

It is suggested that manufacturers note any deviation from their submittal to HITEC when submitting for acceptance of their system byan approving agency.

2 Evaluation of the Maccaferri Terramesh System Retaining Wall

1.2 Documents Reviewed

The documents that provide the basis of the reviews in supportof this report were initially submitted on January 28, 2000. Aninitial review of these documents indicated the need for additionalinformation to complete the submittal. Partial additionalinformation was received on August 14, 2000. Additionalinformation, test data or clarifications were requested and weresubsequently submitted for the record in August 2001,December 2001 and January 2002.

A complete set of the submitted data is available from HITEC,which maintains the-chain-of-custody for all data reviewed andused in this evaluation, including all revisions to the initialsubmittals.

History and System Concept 3

CHAPTER 2

History andSystem Concept

Demonstration of the sinuosity of Terramesh wallinstallation

The Terramesh System is an MSE retaining wall system comprised of stone-filled gabion type baskets for facings and metallicdouble-twisted, grid-type soil reinforcement. Initially introduced in the late 1980’s as a combination of a box Gabion mechanicallyconnected in the field to mesh reinforcement, the system has evolved to the present product, which is manufactured from one

continuous piece of woven mesh.

Terramesh System units are supplied in standard lengths and heights that require site erection. The units are supplied in collapsedform, folded and bundled. The bundles are compressed and strapped together at the factory for easy shipping and handling. Eachbundle is labeled with a tag reporting the size of the units contained.

The standard dimensions of the manufactured units, tabulated below, all have a ± 5% manufacturing tolerance:

The unit length is measured from the front face of the erected Gabion facing basket. Other lengths can be produced by special order.

The double twisted mesh 8x10 type has an internal mesh opening of 3.25 in (83 mm) with an initial wire diameter of 0.106 in (2.7mm) including galvanization which is subsequently PVC coated.

Length Width Height Depth(ft) (ft) (ft) (ft)9 6 1.5 3

12 6 1.5 315 6 1.5 318 6 1.5 39 6 3 3

12 6 3 315 6 3 318 6 3 3

4 Evaluation of the Maccaferri Terramesh System Retaining Wall

The walls may be constructed vertically, however for maintenanceof vertical control during construction, the walls are oftenconstructed with a small batter ranging from 1H:12V to 1H:15V.

The design of this type of structure is fully governed by applicabledesign criteria in AASHTO (2000a).

Maccaferri, Inc. markets the system in the United States andprovides technical design and construction assistance, as wellas the manufactured facing and reinforcement materials.

The first wall constructed in the United States using thistechnology was built in 1992 in Mt. St. Park, Alabama. At present(2001), numerous Terramesh projects have been completed orare under construction both in the United States and worldwide.A detailed listing of projects in the United States and Canadatotaling about 485,00 ft2 (45,000 m2) is provided in AppendixE.

Design Method Evaluations 5

CHAPTER 3

Design MethodEvaluations

Terramesh System wall during installation

3.1 Performance Criteria

The methodology submitted, supported by typical computations, indicates a design practice with respect to Factors of Safety (FS) forexternal and internal stability, foundation embedment, bearing pressure computations and minimum reinforcement length, whichconforms to AASHTO criteria (Article 5.8, AASHTO, 2000a).

With respect to maximum vertical spacing, the submitted design in the upper 4.57 m (15.0 ft) deviates from the maximum recommendedAASHTO vertical spacing of 0.80 m. (2.62 ft), to match the height of one of the standard gabion basket sizes (0.91 m [3.0 ft])manufactured by Maccaferri. As required by Article 5.8.4.1 AASHTO (2000a), the submitted technical justification for the largervertical spacing is described in Section 3.3.

With respect to erection overall vertical tolerances, no actual project data were submitted to indicate that the acceptable tolerances forMSE systems in Demo 82 or AASHTO (2000a) can be met.

Horizontal movements during construction were measured at the FHWA research test wall site in Illinois. A maximum horizontalmovement of just over 1 in (25.4 mm) for the 20 ft (6.1 m) wall was measured. This performance suggests that the overall verticaltolerances in Demo 82 could be met.

The submitted specifications provide no guidance on required erection tolerances.

Regarding the facing unit(s) tolerance to differential settlement, no estimate or data was presented to indicate a maximum level thatwould affect performance or require maintenance. Review of the technical literature for gabions suggests these systems have significantflexibility. Therefore, differential settlements limited to 1/50 to 1/100 should be considered as a guide, at present, to ensure minimalmaintenance or acceptable performance.

6 Evaluation of the Maccaferri Terramesh System Retaining Wall

3.2 External Stability

The submitted methodology for external stability computationsunder static loading (dead and live load) conforms to AASHTO(2000a) criteria. The project owner is responsible for providingstrength parameters for the retained fill as well as allowablefoundation bearing pressures, anticipated foundation settlement,and global stability determinations for each structure.

3.2.1 Global Stability

Maccaferri has developed a computer program (MAC S.T.A.R.S.)for global stability analysis of simple walls and complex tieredstructures. The use of this or other global stability programs ingeneral use is consistent with current practice; however theaccuracy and assumptions used in the program have not beenreviewed. The program should be considered applicable foranalyses of global stability only (i.e., critical surfaces beyondthe extent of the reinforcements).

3.3 Internal Stability

The submitted methodology for internal stability computationsunder static and seismic loading conforms to AASHTO (2000a)and Demo 82 criteria for extensible reinforcements, with respectto:

n Assumed failure surface for internal stabilitycalculations and calculations for effective length Le

n Horizontal stress computations using Kan Distribution of surcharge and concentrated loadsn Development of seismic loads and calculations to

preclude pullout or rupture

The in isolation failure strain of the Terramesh metallic twistedmesh reinforcement is greater than 12 percent. However, thefailure strain of the mesh tested in a confined environment in asand box is less than 3 percent. This behavior qualifies thematerial as an extensible reinforcement, because the failure strainof the mesh is greater than that of the granular reinforced fillmaterial specified for construction.

The current design practice for the upper 15 ft (4.6 m) of aTerramesh wall typically utilizes, where possible, a vertical

reinforcement spacing of 3 ft (0.91 m) to match the height of acurrently manufactured gabion face unit. This spacing exceedsthe recommended AASHTO (2000a) spacing of 0.8 m (2.6 ft).The technical justification provided for the larger spacing, asrequired by Article 5.8.4.1 (AASHTO, 2000a), is based on theresults obtained from a fully instrumented test wall in Illinois ata FHWA test site. The 1987 test wall was constructed with 3-ft(0.91-m) vertical spacing for the full height of a 21 ft (6.4 m),and utilized gabion face baskets 3-ft (0.91-m) wide. Theinstrumentation indicated the face units did not bulge or slide attheir interfaces, and that the wall overall horizontal deflection ofthe face was just over the MSE limit of 13 mm per 3 m (1/2 inper 10 ft). The test wall performance suggests that the larger 3ft (0.91 m) spacing are technically feasible and could beconsidered especially where face deflection greater thannormally specified for MSE walls can be tolerated.

With respect to design parameters needed to determine spacingand sizing of the reinforcement to preclude pullout or rupture,the submitted data for interaction coefficients and allowablestrength are discussed in the following sections.

3.3.1 Interaction Coefficient

The normalized Friction Factor, F*, used in AASHTO (2000a)and Demo 82 was developed primarily by laboratory and fieldtesting by STS Consultants, Ltd. in 1988 and 1997 andsubsequent laboratory testing by Bathurst, Clarabut GeotechnicalTesting (BCGT) in 2001. The laboratory testing used methodssimilar to the methods outlined in Demo 82, Appendix A, exceptthat no internal strain measurements were made in the 1997test series to determine the pullout load at a maximum 15 mm(0.6 in) deflection measured at the back end of reinforcementmesh. Therefore, only the 1988 and 2001 test series is strictlyapplicable in determining the normalized friction parameterF*.

The field pullout test performed at the FHWA research test wallin Illinois yielded results to confirm the applicable laboratorydata. Review of all of the relevant pullout test data for the double-twisted, PVC-coated grid-type reinforcement, indicates that theinteraction coefficients are principally affected by the grain sizecharacteristics of the reinforced fill and to a minor extent by theheight of fill above the reinforcement.

The most recent BCGT pullout test data for a range of reinforcedzone backfill soils permitted by Demo 82 indicates F* ranges

Design Method Evaluations 7

between 0.18 to 3.5, where higher values of F* are associatedwith a coarse gravelly soil. This range is consistent with previoustest results both in the laboratory and from the limited fieldpullout tests.

The pullout data indicates a very strong dependence onmaximum grain size and grain size distribution as well as normalload with as much as one order of magnitude difference betweenF* associated with a silty fine sand meeting the Demo 82specifications and that of a gravelly sand.

For design, in the absence of site-specific knowledge and grainsize test distribution of the actual backfill, a value of F* = 0.30at the surface decreasing to 0.16 at a depth of 6 m (20 ft) isindicated. This range was established based on the latest seriesof tests conducted by BCGT for silty sand meeting the gradationrequirements for MSE structures.

Where a specific site backfill is tested and subsequently used,higher actual test values may be used.

3.3.2 Corrosion/Degradation

The Terramesh System mesh reinforcement is initially galvanizedto a minimum 244 g/m2 (0.80 oz/ft2), which is equivalent to athickness of approximately 33 mm (0.001 in), and then PVCcoated to a minimum thickness of 0.5 mm (0.02 in). Thecorrosion/degradation resistance is therefore initially subjectto construction damage and subsequently to potentially threestages of degradation due to the composite nature of the coatedwire mesh.

The PVC coating provides the initial protection. Once the PVCprotection is no longer effective and the galvanized wire isexposed, the second level of protection, galvanization, providesadditional protection by it’s sacrificial nature. The final level ofprotection is afforded by a sacrificial metal thickness providedin addition to the requirements for tensile capacity.

The durability of the PVC coating for the normally requireddesign life of 75 to 100 years must be assessed in air inconsideration of it’s use as a facing material, and in ground inconsideration of it’s use as soil reinforcement. In air, the majordegradation mechanism is likely to be exposure to UV radiationand elevated temperature, while in ground the likely oxidativedegradation mechanism is a function of the soil regime and thedamage to the coating during construction filling operations.

The in-air exposure models the durability of the facing and thein-ground degradation models the durability of the meshreinforcement.

The in-air durability of the PVC subject to UV exposure wasevaluated qualitatively from test results obtained from ASTMD1499-99 (2000) and ASTM G-23 (“Standard Practice forOperating Light-Exposure Apparatus (Carbon-Arc Type) Withand Without Water for Exposure of Nonmetallic Materials”) ,which expose the material to UV radiation in a controlled testchamber. The test duration is 3000 hours at 63° C (145° F). AsASTM G-23 is no longer current, further testing was conductedin accordance with ASTM D4355 (2000), a newer, but stillqualitative standard used by the geosynthetic industry, for 500hours. The results from either test method indicated smalldecreases of initial strength and elongation properties. Noextrapolation of these laboratory results to field performancehas been made. The in-air degradation rate of the underlyinggalvanization is not specified by AASHTO or Demo 82 and is afunction of local atmospheric conditions.

Examination by Maccaferri of selected upland completed worksworld wide up to 45 years of age indicates no visible face distress,visible PVC deterioration, especially where substantial vegetativegrowth has covered the facing. Note however that PVCgeomembranes are not recommended by industry for in airexposure use.

The in-ground durability of PVC has been qualitatively evaluatedby examination of published chemical compatibility tables andquantitatively by heat aging tests, which is common polymerpractice for evaluating oxidative resistance of thermoplastics.Chemical compatibility tables suggest poor resistance to organicsolvents, hydrocarbons and strong acids.

Heat aging tests were conducted in general accordance with UL746B (Underwriters Laboratories, 2000), which is a heat agingmethod at multiple elevated temperatures on unstressed samples,for a maximum of 5000 to 6500 hours. Note that no presentcomparable ASTM or AASHTO standard is available for heataging evaluations. Degradation rates are then computed usingconventional Arrhenius modeling using time and retainedstrength or elongation change from retrieved samples from atleast three temperatures as the variables. Often, for thermoplasticmaterials a loss of strength or elongation change of 50 percentis taken as time to embrittlement or loss of function.

8 Evaluation of the Maccaferri Terramesh System Retaining Wall

Heat Aging tests on the base PVC material identified as Apex 88-N394G-5 Natural were conducted at five elevated temperaturesfor a maximum duration of approximately 2200 hours. Theresults were evaluated using conventional Arrhenius modelingand based on the assumption that a measured elongationreduction of 25 percent would be considered as the usefullifetime for the product. The justification for using a 25 percentloss on elongation rather than the 50 percent in UL 746B (1997)was in consideration that the PVC coating would not be subjectedto a greater stress or elongation than the steel wire.

Based on heat aging test results, a useful lifetime of 83 years at20° C (68° F) was computed with a correlation coefficient R2 of0.86. A factor of safety of 1.2 to account for precision of test, asomewhat low correlation coefficient and fabrication processfor the material was further recommended, projecting a usefullife of 69 years.

A summary of the Heat Aging Test data is provided in AppendixB.

The in-ground degradation rate of the galvanization is calculatedbased on the corrosion rates given in AASHTO (2000a) andDemo 82 for the specified non-aggressive soil backfill.

The PVC and galvanization is also subject to damage fromconstruction backfill operations. Field installation damage testshave been conducted in the U.K in accordance with BS8006:1995 (2000) to evaluate both the physical level of damageto the coatings and the effect of this damage on the corrosion/degradation mechanisms. The U.K. standard is not as restrictiveas the recently adopted ASTM D5818 (2000).

The results of these field tests indicated that for fine-grainedbackfill meeting the requirements of the standard MSEspecifications; no consistent visible coating damage was noted.Coarse-grained backfill with a 50 mm (2 in) maximum sizeand a grain size distribution within the specifications, were subjectto coating damage averaging three areas of damage per meterwidth (1/ft) of reinforcement. This level of damage can beconverted to represents approximately 12 percent of the area ofreinforcement for which the protective benefit of the PVC couldnot be counted on. Coarser grained soils inflicted levels ofdamage 3 to 4 times greater.

3.3.3 Allowable Strength of Reinforcement

The Terramesh System uses a metallic, soft-temper, double-twisted mesh soil reinforcement, which is galvanized and thencoated with PVC. The reinforcement is manufactured inaccordance with ASTM A975-97 (2000) with a mesh openingof 3.25 in (83 mm) and with 23 longitudinal wires per meter(7.0/ft) of twisted mesh width.

The ultimate tensile strength of the specified soft temper mesh2.7 mm (0.106 in) diameter in accordance with ASTM A641-98 (2000) is 485 MPa (70 ksi) with an elongation greater than12 percent in accordance ASTM A370-92 (2000). Themaximum yield strength is approximately 407 MPa (59.0 ksi)which results in an allowable tensile strength of 0.55 Fy or 224MPa (32.5 ksi) when used as a reinforcement not connected toa rigid facing. The allowable strength must then be reduced forcorrosion degradation effects discussed previously.

The specified zinc coating with respect to weight and qualitymust conform to Class 3 in accordance with ASTM A641-98(2000), which requires a minimum coating weight of 230 g/m2

(0.75 oz/ft2). The PVC coating is applied in accordance with thephysical, chemical and mechanical requirements contained inASTM A975-97 (2000) to a minimum thickness of 1.0 mm(0.04 in).

Considering the data developed in the corrosion/degradationstudies, a PVC design life of 69 years, a galvanization life of 4years, as well as a reduction of cross-sectional steel area of 12percent for construction damage, an allowable strength for in-ground use can be computed. Applying these reductions, aallowable design strength of 26 kN/m (1.8 k/ft) is indicated fordesign for a 75-year structure life. The design life of the facingfor 75 years has not been demonstrated, although it is understoodthat the mesh is generally unstressed and can be visibly inspectedduring its functional use.

3.3.4 Connection to Facing

The standard Terramesh units, facing and reinforcement mesh,is fabricated continuously and therefore no separate connectionto the reinforcement mesh exists nor should be permitted.

Design Method Evaluations 9

3.3.5 Backfill in Reinforced Zone

Select granular fill in accordance with the grain size, soundness,and requirements in AASHTO Division II (AASHTO, 2000b), asoutlined in the Terramesh System Specifications.

3.4 Design Computations

The submitted design computations for three of the four requiredtypical cases (i.e., horizontal backfill, infinite backslope)including seismic considerations were checked and found incompliance with AASHTO (2000a) criteria. The abutment designwas not submitted because the Terramesh System will not bemarketed for this application.

External stability calculations for static and seismic designcomply with the methodology for the typical cases submitted.Internal stability computations are in compliance with respectto methodology.

The coverage ratio for this system is always 100 percent.

Typical computations for the transfer of supplemental loads andin connection with obstructions have not been submitted for review.

Typical computations for the horizontal backfill case arepresented in Appendix B. For conditions where the design stressin the soil reinforcement under seismic loading is exceeded, anon standard solution utilizing double mesh can be considered.This additional mesh is connected to the facing by clips as shownin Appendix B.

3.5 Limitations

The Terramesh system limitations are generally consistent withAASHTO (2000a) limitations. Terramesh use is notrecommended for the following conditions:

n Use as a bridge abutment directly carrying bridgeloads.

n Placement of utilities within the select fill.

n Reinforcement exposed to acid runoff or industrialpollution characterized by low pH, hydrocarbons ororganic solvents.

n Unpredictable erosion or uncontrolled scour depthbelow the reinforced fills zone.

This evaluation has identified a height limitation of approximately10 m (33 ft) for a vertical wall with horizontal backfill. Thislimit is based on the minimum vertical spacing based on standardTerramesh gabion facing baskets and reinforcing mesh, andany backfill meeting the current grain size requirementscontained in the AASHTO or Demo 82 specifications.

3.6 Design Details

Reinforcement length for internal stability should be measuredfrom the back of the facing units as per the submitted calculationsand AASHTO.

3.6.1 Facing

The rock for the facing section of a Terramesh unit shall behard, angular to round, durable and of such quality that it shallnot disintegrate on exposure to water and weathering for the lifeof the structure. The rock shall range in size between 4 to 8 in(102 – 203 mm). A minimum of 3 layers of rock must be usedin filling a 3 ft (0.91 mm) basket and 2 layers when filling a 1.5ft (0.460 m) basket. Maccaferri has recommended the followingmaterial specifications:

Architectural variations are only possible by varying the type/color of the stone used to fill the facing baskets.

The minimum constructable radius on curves is reported as 10ft (3 m) for the Terramesh facing units.

3.6.2 Drainage Elements

The wire basket facing of the Terramesh System is filled withrock and contains up to 30 percent void space. A filtrationgeotextile is placed at the interface of the facing basket and thereinforced soil zone to preclude infiltration of fines.

10 Evaluation of the Maccaferri Terramesh System Retaining Wall

Where required by site conditions, a drainage system may berequired at the interface of the reinforced zone and random fillor natural ground as for all other MSE systems.

3.6.3 Barriers, Copings and Connections to Appurtenances

No detail has been provided for copings or smaller height unitsto better follow inclined finished grades.

The posts for appurtenances such as handrails, guardrails, andsignposts are cast in place within the top basket to provideinterconnection and stability. No calculations in support and/orsizing were provided for review.

Property Acceptable Value Test Method

Unit Weight 24 kN/m3 (150 lb/ft3) Not supplied

Absorption Less than 4.2% loss AASHTO T-85

Abrasion (500 revolutions) Less than 20% loss AASHTO T-96

Freezing and Thawing Less than 10% loss, 12 cycles AASHTO T-104

Magnesium Sulfate Less than 15% loss, 5 cycles AASHTO T-103

Wetting and Drying No major cracking Not supplied

Crash barrier testing has not been performed to substantiate thedesign detail.

Available blocks, joint details, and corner elements are presentedin Appendix C. A slip-joint detail was not submitted.

3.6.4 Obstruction Avoidance Details

No details have been submitted to demonstrate an understandingof AASHTO requirements with respect to major obstructions tothe normal placement of the reinforcement.

Construction Specifications 11

CHAPTER 4

ConstructionSpecifications

Compaction of the backfill

The submittal suggests that the Terramesh System construction methods specifications are intended to be in general conformancewith the applicable provisions of the specifications for MSE Walls, Sections 8.8, from Demo 82. Significant editorial andtechnical revisions to the base specifications (Section 8.8) would be necessary to produce an appropriate specification as

described below.

4.1 Description

Editorial changes are needed to reflect the use of PVC coated twisted mesh basket facing which are continuous with the wire meshreinforcement.

4.2 Materials

Substitute the following for Reinforced Concrete Facing Panels, Soil Reinforcement and Attachment Devices, Joint Materials andLeveling Pad.

4.2.1 Facing Baskets

The facing baskets woven wire mesh shall be manufactured in strict conformance with the provisions of ASTM A975-97 “StandardSpecifications for Double Twisted Hexagonal Mesh Gabions and Revet Mattresses (Metallic-Coated Steel Wire or Metallic-Coated SteelWire With Poly (Vinyl Chloride)(PVC) Coating)” (2000). Specifically the facing basket shall be manufactured using an 8´10 GabionPVC coated twisted wire mesh in accordance with the dimensions and other requirements of Table 1 of ASTM A975-97 (2000).

12 Evaluation of the Maccaferri Terramesh System Retaining Wall

The Terramesh System shall be manufactured with allcomponents mechanically connected at the production facility.The external face, reinforcing panel, and lid shall be woven intoa single unit. The ends, back and diaphragm shall be factoryconnected to the base. All perimeter edges of the mesh formingthe basket shall be selvedged with wire having a larger diameter.

The facing element of the unit shall be divided into two cells bymeans of a diaphragm positioned at approximately 3 ft (910mm) centers. The diaphragm shall be secured in position to thebase so that no additional lacing is necessary at the job site.

4.2.2 Ring Fasteners

Overlapping stainless steel fasteners may be used in lieu of lacingwire for basket assembly and installation. The fasteners shall beof stainless steel, 0.120 in (3.05 mm) in diameter manufacturedin accordance to ASTM A313-98, Type 302, Class I (2000). Thetensile strength shall be in the range of 222 to 253 ksi (1530 -1750 MPa) as measured in accordance with ASTM A313-98(2000).

4.2.3 Facing Infill Rock

The rock used to fill the facing basket shall be hard, angular toround and durable. The rock shall range in size between 4 in(102 mm) and 8 in (203 mm) and conform to the requirementsin Section 3.6.1 Facing.

4.2.4 Soil Reinforcement

The reinforcing woven wire mesh shall be manufactured in strictconformance with the provisions of ASTM A975-97 (2000).Specifically the facing basket shall be manufactured using an8´10 Gabion PVC coated twisted wire mesh in accordance withthe dimensions and other requirements of Table 1 of ASTM A975-97 (2000).

4.2.5 Select Granular Material

The following minor change is required to the gradation limitfor the reinforced zone fill:

Percent passing 50 mm=100

4.3 Construction

Wall erection. Delete 2nd paragraph and add the following:

The facing section of the units are assembled individually byerecting the sides, back, ends, and diaphragm, ensuring thatthe panels are in the correct position, and the tops of all sidesare satisfactorily aligned. The four corners of the basket shallbe connected first, followed by the internal diaphragm to theoutside walls. All connections shall be made using lacing wireor the ring fasteners detailed under Materials and require anominal overlap of 1 in (25 mm) after closure.

The Terramesh units shall be carried to their final position andconnected with the adjoining empty units along the vertical andtop edges of their contact surfaces using lacing wires or ringfasteners. For more than one layer of units, the upper layer shallbe connected to the top of the lower layer along the front andback edges of the contact surface using lacing wire or ringfasteners.

The facing baskets shall be filled with rock as specified underMaterials. During the filling operation manual placement isrequired to minimize voids. The exterior of the basket shall becarefully placed to ensure a flat and compact appearance. Thefill material shall be carefully placed to ensure that the PVCcoating is not damaged.

The cells shall be filled in stages 9 to 12 in (230 to 305 mm) inheight and to a depth not exceeding 1-ft (305-mm) higher thanthe adjoining cell. Connecting wires shall be installed after theplacement of each layer. The cells shall be slightly overfilled toallow settlement of the rock infill and the lid pulled tight untilthe lid meets the perimeter edge of the basket. The lid shall betightly laced and/or fastened along all edges, ends, and topdiaphragms.

Prior to the placement of the granular fill in the reinforced soilzone, the specified geotextile filter shall be placed at the facingsection with a 12 in (305 mm) return at the top and bottom.

Quality Assurance/Quality Control Systems 13

CHAPTER 5

QualityAssurance/Quality ControlSystems

Terramesh Wall used for road embankment

An undated Quality Assurance Manual has been developed and submitted for review for the manufacture of the Terrameshsupplied materials.

5.1 Galvanization

All galvanized wire is purchased from U.S. manufacturers/suppliers of wire product and is provided with a full heat or coil traceability and certification with respect to chemistry, tensile strength and galvanization. The current supplier QC manual has beenreviewed and is consistent with industry standards as evidenced by the ISO 9002 certification. The QA Manual provided for internalQA checking by Maccaferri of product from new suppliers only.

5.2 PVC Supply

PVC pellets are currently purchased from one supplier and each shipment is provided with certification attesting to compliance withthe chemical and physical properties required for gabions under ASTM A975-97, section 8. QC manuals from the supplier, TeknorApex Company, have been reviewed and are consistent with industry standards as evidenced by the ISO 9001 certification.

5.3 Terramesh PVC Coating and Manufacture

The PVC coating is applied to the wire by an extrusion process at a Maccaferri, Inc. facility. The thickness of the coating is automaticallycontrolled and every batch is measured for Q/C compliance.

The PVC-coated wires are used during spiral processing to produce the mesh. The QA manual provides no information as to anyprocess control nor the frequency of any inspections or measurements of mesh openings and length of the finished product.

14 Evaluation of the Maccaferri Terramesh System Retaining Wall

5.4 Ring Fasteners

The hog rings used for lid closure are manufactured by StanleyFastening Systems. A QC Manual was provided, reviewed andfound to be consistent with industry standards.

5.5 Construction and Quality Control Manual (Installation Manual)

A Product Installation Guide (Guide) was submitted andreviewed. The Guide details the erection procedures for thefacing system, materials supplied by Maccaferri, Inc., andmaterials supplied by the erection contractor. This manual isvery brief and should be used with the materials and methodsspecifications outlined in Section 4.0. The Guide requires nodocumentation requirements.

5.6 Design QA/QC

Owners perform design for the Terramesh System and/or theirconsultants, with technical support provided by the Maccaferri

engineering staff. If requested, the Maccaferri Group will contractwith independent consultants to provide the required designservices.

5.7 Warranties and Insurance

Maccaferri does not warranty or guarantee the constructedstructure using their product.

Maccaferri maintains property and casualty insurance. Thecommercial liability insurance provided coverage for Productsand Completed Operations to the following limits:

Amount: $ 5,000,000 General Aggregate$ 2,000,000 Products and Completed OperationsAggregate$ 1,000,000 Each Occurrence

Basis: Claims MadeInsurer: Not disclosedEffective Dates: Not disclosedRenewal: Renews annually

Performance Review 15

CHAPTER 6

PerformanceReview

Terramesh System compined with Green Terramesh forroad project

Terramesh System walls have been constructed since 1990 with over 130,000 m2 (1,400,000 ft2) of wall completed worldwideand 485,00 ft2 (45,000 m2) in the United States and Canada. In the United States 31 structures have been completed (2000)ranging in height from 2 to 12.8 m (6.5 to 42 ft). Project information and contact personnel are provided in Appendix E.

No performance case studies of commercially constructed walls have been submitted for review. Maccaferri states that no performanceproblems have been encountered to date, other than some ascribed to foundation distress. No details of the latter were submitted forverification.

A 21-ft (6.4 m) high, extensively instrumented Terramesh System Wall was constructed at an FHWA-sponsored research facility inIllinois in 1987. The measured performance data confirmed the extensible behavior of the woven mesh reinforcement, measuredreinforcement stress levels, field and laboratory pullout parameters and horizontal deflections.

6.1 Costs

Insufficient actual cost has been provided for future guidance.

Project information and contact personnel for the bid projects are also enclosed in Appendix E.

References 17

References

American Association of State Highway and Transportation Officials (AASHTO). 2000a. Interim Standard Specifications for HighwayBridges, American Association of State Highway and Transportation Officials, Washington, D.C., 16th Edition.

American Association of State Highway and Transportation Officials (AASHTO). 2000b. Interim Standard Specifications for TransportationMaterials and Methods of Sampling and Testing. Part II Tests, American Association of State Highway and Transportation Officials,Washington, D.C.

American National Standard (ANSI/UL). 2000. American National Standard/Underwriters Laboratories 746B. “Standard for PolymericMaterials – Long Term Evaluations”.

American Society for Testing and Materials (ASTM). 2000. ASTM A313/A313M-98, “Standard Specification for Stainless Steel SpringWire,” American Society for Testing and Materials, West Conshohocken, PA.

American Society for Testing and Materials (ASTM). 2000. ASTM A370-01 Standard Test Methods and Definitions for MechanicalTesting of Steel Products,” American Society for Testing and Materials, West Conshohocken, PA.

American Society for Testing and Materials (ASTM). 2000. ASTM A 975-97, “Standard Specifications for Double-Twisted HexagonalMesh Gabion and Revet Mattresses (Metallic-Coated Steel Wire or Metallic-Coated Steel Wire With Poly(Vinyl Chloride) (PVC) Coating)Glass Fiber Strands,” American Society for Testing and Materials, West Conshohocken, PA.

American Society for Testing and Materials (ASTM). 2000. ASTM A 641/A641-M98, “Standard Specifications for Zinc-Coated(Galvanized) Carbon Steel Wire, American Society for Testing and Materials, West Conshohocken, PA.

American Society for Testing and Materials (ASTM). 2000. ASTM D1499-99, “Standard Practice Filtered Open-Flame Carbon-ArcType Exposures of Plastics,” American Society for Testing and Materials,” West Conshohocken, PA.

American Society for Testing and Materials (ASTM). 2000. ASTM D4355-99, “Standard Test Method for Deterioration of Geotextilesfrom Exposure to Ultraviolet Light and Water (Xenon-Arc Type Apparatus),” American Society for Testing and Materials, WestConshohocken, PA.

American Society for Testing and Materials (ASTM). 2000. ASTM D5818-95, “Standard Practice for Obtaining Samples of Geosyntheticsfrom a Test Section for Assessment of Installation Damage,” American Society for Testing and Materials, West Conshohocken, PA.

American Society for Testing and Materials (ASTM). 2000. ASTM D 638-98, “Standard Test Method for Tensile Properties of Plastics,American Society for Testing and Materials, West Conshohocken, PA.

18 Evaluation of the Maccaferri Terramesh System Retaining Wall

British Standards Institute (BSI). 2000. BS 8006:1995, “Code of Practice for Strengthened/Reinforced Soils and Other Fills,” London,United Kingdom.

Elias, V. and B.R. Christopher. 1996. Federal Highway Administration (FHWA) SA-96-071 (Demonstration Project 82) MechanicallyStabilized Earth Walls and Reinforced Soil Slopes, Design & Construction Guidelines, Office of Technology Applications, FederalHighway Administration, Washington, D.C.

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