Demonstration Projects Division 

Office of Hiahway Operations 

FHWA-DP-90-068-003 

April 1990 

Archived
Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Reaplent’. Catalog No.

FHWA-DP-90-068-003

4. Tit19 and Subtitle 5. Report Dote

DP-68 - Permanent Ground Anchors April 1990

Volume 1, Final Report 6. Performing Organization Code

HHO-42

7. Author’s)

8. PerformIng Organization Report NO .

Richard S. Cheney

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

HHO-3O/HHO-40

Federal Highway Administration 11. Contract or Grant No.

400 Seventh Street, SW.

LJashington, D.C. 20590 13. TYPO of Report ond Period Covered

12. sponsoring Agency Name and Address

,

HHO-40 Final Report

Federal Highway Administration

400 Seventh Street, SW. 14. Sponsoring Agency Code

Washington, D.C. 20590

15. Supplementary Notes

FHWA: Theodore Ferragut

16. Abstract

Ground anchors, often called tiebacks, are structural elements which receive their

support in soil or rock and act to retain earth masses and/or applied structural

loads. The Federal Highway Administration recognized that the use of permanent

ground anchors in highway cut sections could affect substantial benefits in both

economy and safety. The specific purpose of the permanent ground anchor demonstration project was to introduce the concept of permanent ground anchor use into

American construction practice. A manual numbered FHWA-DP-68-1R and titled

"Permanent Ground Anchors" was prepared and several thousand copies distributed to

highway engineers. Permanent ground anchors on several projects were monitored to

validate the concepts addressed in FHWA-DP-6%1R. This report summarizes the

results of both the field monitoring and the history of the permanent ground anchor

demonstration project.

17. Kep Words 18. Distribution Statamwtt

Permanent ground anchors, tiebacks, No restriction - NTIS

anchors, anchor specifications, anchor

test projects, anchor acceptance criteria,

anchor test procedures

19. Security Clarrif. (of this rap& 20. Security Clorrif. (of this pa901 21. No. of Po9.r 22. Price

Form DOT F 1700.7 (a-72) Reproduction of complrtrd pagr autharizrd

i

Archived
Table of Contents

I . INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

II. DESCRIPTION AND BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

III. PROJECT DEVELOPMENT....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Resolution of Technical concerns . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Cost-Effectiveness of Permanent Anchors................... 7

Permanent Ground Anchor Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Demonstration Project Accomplishments..................... 8

Continuing Developments in Permanent Anchors.............. 10

IV. DEMONSTRATION PROJECTS SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Widening of Existing Urban Interstate Highway

Georgia I-75, Atlanta . . . . . . . . . ..*....................... 11

Repair of Urban Interstate Highway Retaining Wall

Maryland, I-95, Baltimore............................... 12

Pre-design Test Anchor Program

Washington, I-90, Seattle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Correction of Landsllide

Kentucky, KY-227, Carroll County.....,.................. 16

Lateral Support of Bridge End Slopes

Dimond Blvd - Anchorage, Alaska......................... 19

Urban Railroad Grade Separation

North Street Project, Lima, Ohio........................ 20

Tieback Bridge Abutment

Raw? Q, I-279, Pittsburgh, Pennsylvania................. 21

V. REHABILITATION OF STRUCTURES WITH PERMANENT

GROUND ANCHORS.................. . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Hope I Idaho Cemetery Wall Rehabilitation.................. 22

Nevada, Carlin Canyon Portal Rehabilitation............... 24

VI. CONCLUSIONS........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

ii

Archived
APPENDIX

LIST OF FIGURES

Figure Title Paae

1

2

3

3A

3B

3c

3D

3E

Demonstration Presentations Completed A-l

Simple Schematic of a Permanent Anchor A-2

Georgia I-75 Project A-3

Testing of First Anchor Row A-3

Forming Concrete Wall Face Over Anchors A-3

Final Wall, 1984 A-4

Wall, 1988 A-4

4

4 A

4B

4c

4D

4E

5

SA,SB

Stable Roadway, 1988

Above Wall-No Pavement Cracks

Maryland I-95 Project

Wall Joint Spalling, 1980

Wall Base Translation, 1980

TMD Anchors Installed, 1981

Anchor Testing

Final Wall, 1984

Washington I-90 Project

Anchors Installed Through Existing

Cylinder Pile Wall

SC,SD Instrumentation for Anchor Testing

6 Kentucky Route 227 Project

6A Embankment Stable With No Evidence of Movement

6B,6C

6D

3 Years after Construction

Views of Wall Face 4 Years After Construction

Termite Infestation of Permanent Treated Wood

Face

6E Blistering and Peeling of Protective Coating

on Waler A-13

7 Alaska Dimond Boulevard Project

8

8A,8B,8C

8D,8E

8F

8G,8H

9

9A

9B

9c

Completed Dimond Boulevard Wall

Ohio Lima Project

Building Underpinning Operations

Anchor Drilling

First Level Anchors Installed

Opposing Views of Completed Walls, 1989

Idaho Hope Project

Hope Wall Condition, 1980

Close-up of Crack in Lower 12 feet of Wall

New Reinforced Fascia Wall Poured Prior to

Anchor Installation

9D Completed Anchored Wall Repair - 1981

9E Note Small Thickness of Wall Repair

10 Nevada Carlin Canyon Project

10A Completed West Portal, Carlin Canyon Tunnel

10B

Vertical Beams Contain Anchors A-22

Completed East Portal, Carlin Canyon Tunnel A-22

A-5

A-6

A-6

A-6

A-7

A-7

A-8

A-9

A-9

A-10

A-11

A-11

A-12

A-13

A-14

A-15

A-15

A-16

A-17

A-18

A-19

A-19

A-19

A-20

A-20

A-21

A-22

iii

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I. INTRODUCTION

Ground anchors, often called tiebacks, are structural elements

which receive their support in soil or rock and act to retain

earth masses and/or applied structural loads. Temporary ground

anchor systems were introduced in the United States several years

ago to support excavations while the permanent facility was

installed. This temporary support system gained wide acceptance

because of economic and safety aspects. However, American

engineers hesitated to accept the permanency of ground anchors for

a variety of reasons; particularly, a perceived lack of design and

construction experience and documented design techniques.

The Federal Highway Administration (FHWA) recognized that the use

of permanent ground anchors in highway cut sections could affect

substantial benefits in both economy and safety. The economy

results from elimination of temporary support systems and reduced

right-of-way considerations. Safety is improved by eliminating

cramped excavations cluttered with delicate bracing, and reducing

the time and area required for standard construction methods.

Special benefits accrue in urban areas where adjoining facilities

must be supported during construction. Often the area saved by

utilizing permanent ground anchors can eliminate the need for

underpinning nearby structures.

The specific purpose of the permanent ground anchor demonstration

project was to introduce the concept of permanent ground anchor

use into American construction practice. A manual numbered

FHWA DP-68-1R and entitled "Permanent Ground Anchors" was prepared

and several thousand copies distributed to highway engineers. The

manual contains a comprehensive review of current design and

construction methods. The recommended guideline procedures insure

that agencies adopting permanent ground anchors will follow a safe

rational procedure from site investigation to construction. Close

attention was given to presentation of suggested general

specifications and plan details. These contract documents provide

the transition from design analyses to field construction and

frequently decide the success or failure of new concepts such as

this. Every effort was made in these sample specifications to

allow the experienced anchor contractor to use innovative methods

or equipment in construction. Such specifications are needed to

encourage contractors to seek cost-effective improvements to

current anchoring methods.

The information in the DP-68-IR report was primarily based on:

1 . existing technical literature on ground anchors,

2 . reports from FHWA research projects performed from

1979-82,

volumes),

including FHWA/RD81/150 through 152 (3

"Permanent Ground Anchors," and

FHWA/RD82/047, "Tiebacks," (reference copies of

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which are available to the public from the

National Technical Information Service,

Springfield, Virginia, 22161),

3 . field inspections of permanent anchor projects

during and after construction,

4 . cooperative efforts between Federal and State

engineers to prepare design calculations,

and specifications for pilot test projects,

plans,

5 . instrumentation of selected permanent anchors.

In 1984, formal presentations of the demonstration project were

made to public agencies. The presentation consisted of

hour segments,

four, linformation

which introduced and briefly explained the detailed

contained in the manual. The object of the

presentations was to reach as many engineers as possible in a

short period of time to promote the concept of

anchoring.

permanent ground

Over 50 demonstration presentations were made in a

a-year period to engineers in 42 States. Figure 1 indicates the

States where presentations have been given. In-depth technical

assistance was then provided to highway agencies on a one-to-one

basis when specific projects arose. Currently, 31 States have

either constructed permanently anchored structures, or

have permanently

currently

anchored projects in design. Numerous

specialized presentations on construction,

specification

inspection, or

preparation have also been completed.

on construction inspection has been prepared for

A videotape

agencies.

use by highway

During the demonstration presentations, several proposed highway

projects with permanently anchored structures were identified as

candidates for instrumentation and performance monitoring.

Cooperative Agreement Work Orders were issued to those agencies.

The Work Orders provided a work plan and a schedule for

reimbursement of funds necessary to instrument, monitor, and

report on the long-term performance of the permanently anchored

structures. The period of

5 years or less.

time for monitoring was generally

Accepted reports from five such demonstration

projects are included in the appendices of this report.

Coordination with technical groups has resulted in the preparation

of standard specifications to nationally regulate the construction

of permanent ground anchor walls. In 1986, the Post

Institute published

Tensioning

"Recommendations for Prestressed Rock and Soil

Anchors." More recently, Task Force 27, AASHTO, ARTBA and AGC

Joint Committee, has prepared both a construction specification

and an inspector's manual for permanent ground anchors.

and dissemination

Approval

1990.

by AASHTO of both documents are anticipated in

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II. DESCRIPTION AND EACKGRODND

Within the past 20 years, many ground reinforcement techniques

have been successfully introduced to American civil engineering

practices after an extended period of use in Europe. The latest

and possibly the most significant entrant is the permanent ground

anchor. More precisely, the permanent ground anchor referred to .

this report ' corrosion-protected, prestressed, cementiiouted tendon whizfl rnty be installed in soil or rock. Very

broadly described, a ground anchor is a device which mobilizes and

transfers a resisting force from the ground to a structural

element such as a wall or slab. Although similar in function and

looks, the permanent anchor, is not to be confused with the

temporary tieback or mechanical anchor or resin rock bolt. In the

remainder of this report, the word "anchor" when used shall mean

permanent ground anchor unless otherwise specifically stated.

Figure 2 shows a schematic of a typical anchor.

These anchors are generally inserted in a hole which is drilled or

driven into soil or rock. Certain basic anchor terms will now be

introduced which will be used throughout this report. Specific

anchor details will be reserved for explanation in applicable

sections.

Basic anchor components frequently referred to are:

1 . The prestressinq steel --commercially available in

single or multiple wires, strands, or bars

comprising:

a. the bond lenqth--that portion of the

prestressing steel fixed in the primary grout

bulb, through which load is transferred to the

surrounding soil or rock, and

b. the unbonded lenath--that portion of the

prestressing steel which is free to elongate

elastically and transmit the resisting force

from the bond length to the structural element

(i.e., the wall face, etc.).

2 . The anchorase--a device usually consisting of a plate

and an anchor head (or threaded nut) which permits

stressing and lock-off of the prestressing steel.

3 . The orout--a portland cement based mixture which

provides corrosion protection as well as the medium

to transfer load dram the prestressing steel to the

soil or rock.

Anchors were introduced in the 1930s and, by the 196Os, were in

common use for major structures of all types.

successful widespread

The keys to

use in Europe were both social and

technical. The scarcity of land available for construction,

3

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particularly in urban areas, required excavation and retention

techniques that could be accomplished with minimum disturbance to

land owners or the traveling public. Anchored walls substantially

reduced the amount of land required for construction while also

reducing the project cost. Equally as important was the assurance

that this technique was safe and could be easily controlled in

construction. European engineers spent many years developing and

refining public design and construction codes for anchors. Based

on field experience and long-term observation, these codes

guaranteed the safety of each anchor by requiring testing to

beyond proposed design loads. Continuing historical development

now relates mainly to refinement of corrosion protection systems,

load transfer of anchor forces into the ground, the form of

tension members, and grouting methods. In some countries, anchor

contractors must pass acceptance tests before being allowed to

install anchors. These acceptance tests involve installing and

excavating, for government inspection, a large number of anchors

according to the prevailing code. The data from such tests,

although very costly, has contributed much to the development of

anchor use worldwide.

Until the late 197os, the only common use of anchors in the

United States was to support temporary excavations. Although the

United States' first permanent soil anchor was installed in

Detroit, Michigan, in 1961, relatively few public agencies had

incorporated anchors in major permanent structures as of the

inception of this demonstration project. The reasons for this

hesitancy were:

1 . the scarcity of American anchor design and construction

experience; i.e., how do we design it and who can we

trust to properly install it?

2 . the concern of anchor permanency against long-term

corrosion or creep; i.e., how long will anchors last and

safely carry design loads?

3 . the delineation of proper areas for cost-effective

application; i.e., where and how many do we use?

4 . the constraints of contracting procedures used by public

agencies; i.e., how do we insure quality from the low

bidder?

In 1979, FBWA Demonstration Projects Division

authorized project development

(FBWA-DPD)

to begin on the permanent anchor

project. A project manager and a technical advisory committee

were appointed. A work plan was

anchor technology and

developed to study existing

installations; determine areas where

additional work was needed; update existing technology; prepare a

basic design manual; and solicit test installations on highway

projects. The objective was to provide highway agencies with

adequate knowledge to permit confident, routine use of

anchors.

permanent

4

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III. PROJECT DEVELOPMENT

Resolution of Technical Concerns

A review of existing technical literature on anchors confirmed

that most work had been done by the Europeans. Unfortunately,

little documentation of design methods for anchors was available.

This information void was a direct result of how anchor work was

contracted for in Europe. Nearly all European anchoring is done

on a design-construct, turnkey basis by specialist firms who, in

many cases, are pre-qualified to do anchor work by the government.

These firms have developed proprietary design and construction

procedures which are not released even to their clients.

For successful introduction of anchors into the United States, the

contracting approach promoted by the demonstration project would

need to conform to the current competitive bid procedures used by

State agencies. This approach required both general design

guidelines and a detailed construction specification. A threepronged path was chosen which involved initiation of research in

design aspects, field inspection of on-going permanent anchor

construction projects, and development of an easy-to-understand

yet comprehensive construction specification.

In 1980, two basic design questions remained to be answered before

the demonstration project could proceed--documentation of both

techniques to determine anchor capacity and longevity aspects of

both anchor materials and bond strengths. The former question was

addressed by awarding research contracts to three experienced

anchoring firms --Soletanche-Rodio, Nicholson, and StumpVibroflotation, who independently prepared design manuals

respectively numbered FHWA RD 81/150; 81/151; and 81/152. Each

manual contained a detailed explanation of the firm's general

design procedure as well as three documented case histories

illustrating use of the design procedure and the computations for

a test project provided by FHWA. Although each firm used

different analyses, the basic method of design was the same; i.e.,

the critical failure surface was located and the bond zone of the

anchor founded beyond the failure plane. Load testing of all

installed anchors was considered an extension of design as no

design method existed to reliably predict, from subsurface data,

the exact bond zone dimensions necessary to safely carry a

particular anchor load. These two concepts provided the basis for

the current anchor design practice in the United States.

The longevity aspects were addressed by the Schnabel Foundation

Company in FHWA RD 82/047, "Tiebacks." In this publication,

methods of corrosion protection for permanent anchors were

detailed and recommendations given as to their use. The creep

behavior of anchors was also thoroughly investigated. Specific

recommendations were presented for anchor testing procedures and

acceptance criteria to insure long-term anchor load capacity at

acceptable deflections. Lastly, contracting guidelines for

permanent anchor work were presented. Important concepts such as

5

Archived
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pre-qualification of anchor contractors, performance-type

specifications, and shared design responsibility between owner and

contractor were recommended for reliable, cost-effective anchor

work.

In reviewing the uses of permanent anchors, the permanently

anchored retaining wall application was by far the most common and

economically attractive. A decision was made to concentrate the

design section of the FHWA DP 68 manual on permanent anchor wall

design. The design procedure initially adopted for the

demonstration project relied heavily on concepts developed from

braced wall systems as well as the aforementioned research

efforts. In technical areas where conflicting observations or

theories could not be resolved, the design procedure chose the

more conservative position. The rationale for this decision was

that instrumentation of initial anchored wall installations would

be encouraged. Highway agencies could then compare actual

measured parameters with assumed. As a database was developed,

various parameters could be confidently changed to less

conservative values.

In 1979-80, concurrent with the above research efforts, the Post

Tensioning Institute formed an ad-hoc committee to revise the

existing guidelines for anchor use. The committee was composed of

anchor contractors, producers, consultants and users. The

resulting publication, "Recommendations for Prestressed Rock and

Soil Anchors," printed in 1980 and revised in 1986, established

national standards for design and construction of anchors. These

standards, which were written in a simple format, were adopted by

many private and public organizations as the basis for their

construction specifications. Much of the information in this

publication was used to develop the guideline permanent anchor

specification for the demonstration project.

The resulting construction specification, published in the

FHWA DP-68 manual for permanent anchors, was a performance-based

specification. This wJ?e of specification was a departure from

the prescription-type specifications used by public highway

agencies on other highway items. The proposed anchor

specification contained some prescription verbiage to control the

materials used and certain basic construction operations.

However, the contractor was permitted, with few constraints, to

choose and control the method of drilling, the tendon type, the

drilled hole diameter, the bond zone dimensions and the total

anchor length. The performance aspect was that the contractor was

responsible to produce an anchor which would pass certain

acceptance test criteria established in the specification before

receiving payment for the anchor. In short, the contractor was

responsible for determining anchor installation procedures to

obtain a desired anchor capacity selected by the agency.

The key element in the performance specification was prequalification of the contractor who would perform the anchor work.

Permanent anchoring was recognized by researchers, technical

6

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groups r and construction inspectors to be a specialty type of

work. Furthermore, successful introduction of permanent anchoring

into highway agencies depended on their first project being a

success. Few agencies had any construction personnel who were

knowledgeable of proper permanent anchor construction techniques.

Specifying a specialist would permit the construction personnel to

observe proper techniques and develop inspection expertise which

could be used on later projects where the agency relaxed the prequalification criteria.

Cost-Effectiveness of Permanent Anchors

After technical concerns had been addressed to the satisfaction of

the technical advisory committee, the permanent anchor technology

was ready to be disseminated. Early in the demonstration project,

data had been collected from a few permanent anchor projects done

prior to 1980, which indicated the per-square-foot wall cost to be

between $30 and $40. At that time, standard concrete retaining

walls in cut situations were averaging about $75 per square foot.

However, the cost effectiveness of the design technique and the

performance specification approach needed to be demonstrated

before promoting routine consideration of permanent anchor systems

nationwide to highway agencies. A review of cost data from a few

private and public anchor wall projects indicated a cost of about

$45 per square foot of wall face. Two State highway agencies,

Georgia and Maryland, were identified by FHWA regional

geotechnical engineers as having projects in design which were

appropriate for a permanent anchor alternate design.

The project manager provided design computations, plans, and

specifications for an alternate anchor

locations.

wall design at both

In Georgia,

the standard Georgia

both the alternate anchor wall design and

DOT retaining wall design were included in

the contract documents for the I-75 project with instructions that

contractors were to bid one or the other. The final bid

tabulation showed that seven of

submitted bids

the eight contractors who

(including the low bidder) had selected the

alternate anchor wall design. The bid price for the anchor wall

alternate was about $36 per square foot;

($410,000) th

about 40 percent lower

an either the "as bid" or Engineers' estimate for the

standard Georgia retaining wall. In Maryland, the estimated cost

of the anchor wall design was so much less than the standard

design that the standard design was deleted from the contract.

The "as bid" price for the anchor wall was about

foot; a savings

$36 per square

of approximately 40 percent ($461,335) over the

conventional design. Two anchor walls constructed

State during

in Washington

the same time period had bid prices between $41 and

$44 per square foot.

design

It was evident that a permanent anchor wall

was economically competitive with

currently in use for walls in cut.

standard designs

Archived
DP68 - final report

Permanent Ground Anchor Manual

In 1984, FHWA-DPD published definitive recommendations in DP-68-1,

"Permanent Ground Anchors," to answer those previously stated

concerns of public agencies who were hesitant to specify permanent

anchors. This manual presented, in detail, all basic concepts

necessary for a highway agency to incorporate permanent anchors on

a project.

investigation,

Chapters were included on application criteria, site

system design,

principles of anchor design, anchored

specifications,

load testing/stressing,

corrosion,

and

preparation of plans/

construction control. The manual was

organized in a manner consistent

highway project.

with the phases of a typical

The emphasis in the manual was on identifying

applications where anchors could be used successfully; providing a

rational, step-by-step procedure for producing a safe, Yet costeffective design; and establishing basic construction controls to

assure a quality final product. The final section of the manual

contained a sample problem and detailed numerical solution which

demonstrated the use of the information presented in the preceding

chapters.

A s clearly stated in the abstract, the manual was not intended to

present state-of-the-art procedures, but rather to serve as an

introduction to basic anchoring concepts.

present basic information in simple,

The objective was to

straightforward terminology

to provide the practicing highway engineer with adequate knowledge

to successfully contract for permanent anchor work.

Demonstration Project Accomplishments

The project accomplishments can be measured in terms of technology

transferred to highway agencies, number of

adopting permanent anchors

highway agencies

for routine highway applications,

performance of anchor walls designed based on the guideline

procedure, and cost effectiveness of permanent anchor designs

nationwide.

Technology transfer

project.

is an important element of any demonstration

Presentations of permanent ground anchor technology were

requested and completed in 42 States to over 3,800 engineers while

the project was active. The project manual, "Permanent Ground

Anchors," was reprinted three times due to heavy demand, with

about 5,000 copies being distributed nationally. The manual is

currently available from the National Technical Information

Service, Springfield, Virginia 22161, under accession number PB85

1780107/AS. In addition, about 500 copies of both the research

publication "Tiebacks" (FHWA RD82/047) and the Post Tensioning

Institute's "Recommendations for Prestressed Rock and Soil

Anchors" were distributed nationally to highway agencies.

At the inception of the project, only three State highway agencies

were employing permanent ground anchors on construction projects.

The project manager provided detailed technical

those highway

assistance to

agencies interested in alternate designs involving

8

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permanent anchors. This assistance involved preparation of

typical design computations, specifications and plans for specific

projects, or review of consultant-submitted designs. At present,

31 States are using permanent anchors; nearly all are using the

design procedures outlined in the FHWA DP-68 "Permanent Ground

Anchor" manual. All walls constructed using these design

procedures have performed satisfactorily after construction. No

walls have failed to perform their design function, whether the

project involved restraint of adjacent buildings, highways or

utilities. The design method has been proven to produce a stable

wall system in a variety of imposed loading situations. The only

question which remains to be answered by future observation and

research is the degree of conservatism of the method. In the

March 1988 reprinting of the "Permanent Ground Anchor" manual, the

minor changes that were made to the example problem design

procedure were the result of observations of the performance of

recently constructed anchor walls.

Interestingly, the cost effectiveness of permanent anchor walls,

even those designed by the admittedly conservative, original

procedure in the manual, far exceeds that of other possible wall

designs in cut situations. Other changes may result when

additional research is completed and evaluated by highway

agencies.

Some highway agency engineers were reluctant to specify a new

technology which did not have a history of use in their State. To

address these concerns and to stimulate highway agency interest in

permanent ground anchors, the Demonstration Projects Division

offered to provide funds for instrumentation and long-term

evaluation of anchor walls. The objectives of the performance

evaluation were both to prove to the agency that permanent anchors

did perform in the long term and to provide highway agencies with

hard data which could be used to refine their design procedures.

The 8 projects selected for construction monitoring cost $406,475

to instrument and evaluate. The reported savings from 4 of these

projects totaled nearly $20 million.

In the past 10 years, the total square footage of permanent anchor

walls being constructed has increased dramatically. The first

anchor wall projects were scattered geographically and involved

wall areas less than 20,000 square feet. Recent projects, such as

I-215 in Salt Lake City, Utah; I-90 in Seattle, Washington; I-10

in Phoenix, Arizona; and I-20 in Dallas/Ft. Worth, Texas, all

involved wall areas greater than 100,000 square feet. Even

relatively small anchor wall projects such as I-90 in Wallace,

Idaho, and I-35 in Duluth, Minnesota, contained in excess of

40,000 square feet of permanent anchor wall.

In 1989, 2 million square feet of anchor wall construction is

projected. Based on previously documented savings, this wall area

use translates into a savings in excess of $70 million in 1989.

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As highway agencies began adopting permanent anchor walls into

routine project designs, the emphasis in the demonstration

projects shifted to construction control. During 1986-88, the

project manager completed presentations to construction inspectors

in 15 States. These efforts were usually done at the project site

just after construction had begun, both to determine which methods

the contractor would use and to allow inspectors to identify areas

where training should be focused. Frequently, the contractors'

personnel were invited to attend these presentations to see the

inspection procedures which would be used on the project.

Continuinc Develooments in Permanent Anchors

By design, the purpose of a demonstration project is to introduce

new technology into routine use by highway agencies and establish

national guidelines for safe, cost-effective use of the

technology. On October 1, 1988, those goals were judged by FHWA

to have been fulfilled and subsequently the permanent ground

anchor project was removed from active status. However, by the

latter stages of the project, involvement was sought of other

technical groups within the highway community to control the

future direction of permanent anchoring.

The AASHTO-AGC-ARTBA Joint Committee Task Force 27 on Ground

Modification was formed on the recommendation of FHWA. A ground

anchor group has been formed within the Task Force to develop

future design and construction standards. The intent is to

provide AASHTO with standards for national distribution.

Currently, three efforts are underway in the group. A permanent

ground anchor generic specification, a ground anchor construction

inspection manual, and

walls.

a design guide for build-down retaining

The specification has been approved by the Task Force and

sent to AASHTO for approval. The inspection manual and design

guide were submitted to the Task Force for approval in early 1990.

The increase in permanent anchor use has generated many new

questions about anchor design and construction techniques.

However, unlike the early research efforts for this project, these

questions relate not to proving whether anchors work but to

refinements to optimize current procedures. Highway agencies who

have adopted permanent anchors into routine construction practice

have initiated operational research which will lead to either

improved techniques or increased anchor usage.

these efforts is

An example of

the Washington State DOT study on seismic

response of tieback walls.

expand anchor use into

The objective of this study is to

seismically active areas

rational modifications to

by developing

current static design procedures. An

upcoming major study, funded by FHWA's Office of Research in 1989,

will focus on refinement of

soil-structure interaction.

those design factors dealing with

Items such as bond zone load transfer

factors, earth pressure distribution,

expected to be analyzed.

and soldier pile design are

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In regard to national standardization of anchor testing

procedures, the American Society of Testing Materials (ASTM) has

formed subcommittee D18.11. The goal of the subcommittee is to

prepare an ASTM standard for tensile load testing of individual

anchors. The standard will include details of the apparatus used

to apply and measure the load, the apparatus for measuring

movements, the loading procedure, safety requirements, and

recording of data. An appendix on proper presentation of test

data will be included.

Although FHWA's role in actively promoting permanent ground anchor

use has been phased out, the interaction during the preceding

years with other technical groups has insured continuing national

development of anchor technology in the future. FHWA will

continue to provide technical assistance on future anchor designs

or technical reviews of new anchor technology. The role of

continued promotion and development rests now with the technical

groups of the highway community.

IV. DEiMONSTRATION PROJECTS SUMMARY

One of the objectives of Demonstration Project No. 68 was to

convince highway agencies to monitor construction performance and

long-term behavior of permanent ground anchored structures. Seven

States participated, each application varying some degree from the

other either in terms of soil conditions, anchored wall design, or

anchor type. Detailed reports by the project's principal

investigators of the results of instrumentation and interpretation

of wall performance are included in the appendices of this report,

except for the Pennsylvania DOT tied back abutment project which

was only constructed in 1988. The following executive summary of

each project highlights basic design and construction information

as well as the primary conclusions for each project.

Wideninq of Existinq Urban Interstate Hiqhwav

I-75, Atlanta, Georqia

The widening of I-75, which is in a cut section through downtown

Atlanta, presented several major problems such as very limited

right-of-way, existing utilities and buildings, traffic

maintenance of 100,000 vehicles per day, and a short time-frame

for construction. A permanent anchored wall design was selected

for use in a critical area near 5th Street, where 30-foot high

cuts would be required near existing facilities. The general soil

conditions consisted of varying mixtures of micaceous sands and

silts over bedrock. These soils are frequently described as

saprolite which denotes residual products of rock decomposition

where deep rock weathering has occurred in a wet, humid climate.

Demonstration project funding for instrumentation, interpretation,

and reporting on wall performance was provided in July 1981 to

Georgia DOT under a Cooperative Agreement. In turn, Georgia DOT

contracted with Law Engineering/Geoconsult International to

perform most of the prescribed tasks in the Demonstration Project

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Cooperative Agreement. The principal investigators were

Messrs. David Mitchell of Georgia DOT and Thomas Richardson of Law

Engineering Consultants. A special

ground

task, unique to this first

anchor demonstration project, was development by a

specialist of a basic,

ground anchor systems.

reliable instrumentation plan for permanent

The intent was

evaluate

to develop, install,

and, if successful, recommend this instrumentation

package on future anchor installations. The instrumentation

report prepared by Mr. John Dunnicliff is attached to the Georgia

I-75, Atlanta report in the appendix.

Figures 3A to 3E show three stages of construction of the anchored

wall including the finished product in 1984 and 1988. All visual

observations and instrument measurements confirm that the wall and

anchors are performing as anticipated in design. Long-term

measurements were taken on 60 vertical and horizontal survey

points established on or behind the wall during construction. The

measurements showed that the movements which occurred indicated

active earth pressure conditions and ceased shortly after

construction was completed. The survey points still available for

reading indicate no definable wall or ground movement has occurred

since 1983.

The measurement of anchor load in selected tendons has been done

periodically since 1983, Three different instruments were used to

monitor load--load cells, rod telltales, and wire telltales.

Strain gages were not used due to problems involving both

attachment to the prestressed strand tendon and the range of

expected microstrains. Although erratic readings were noticed in

various instruments during construction, those instruments which

have continued to function to the present indicate that the load

carried by the anchors has remained relatively constant, with a

range of only 3 kips. A few anchors stabilized at loads which

were slightly higher or lower than the lock-off load,

variance with

indicating

the magnitude or distribution of assumed lateral

earth pressure at that location. These variations had no effect

on wall performance.

Since

DOT has

completion of the I-75 anchored wall at 5th Street, Georgia

completed permanent anchor walls on 12 other highway

projects in the Atlanta metropolitan area. The success of

permanent anchor construction has caused Georgia DOT to routinely

permit alternate designs involving anchored walls on highway

projects.

Reoair of Urban Interstate Hiqhwav Retainina Wall

I-95, Baltimore, Marvland

In 1974-75, a 900-foot long wall with a maximum height of about

25 feet was built to retain an earth cut for Interstate 95. A

steep natural slope rose from the top of the wall

Mount Carmel Cemetery.

to the nearby

was toward the wall.

The natural surface drainage of this area

In addition, the subsurface drainage from

the temporary cut face

wall.

indicated a groundwater flow toward the

Unfortunately, during wall construction, a clay material

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was placed as backfill for the wall, effectively preventing any

drainage. Over a 4-year period, the natural water surface behind

the wall rose from below the wall footing to within 1 foot of the

backslope surface. The hydrostatic pressure increase caused

substantial movement of the wall. Spalling of wall joints and

base translation caused an upheaval of the I-95 pavement when the

passive resistance in front of the wall was exceeded (see

Figures 4A-4B). Slope inclinometers, which were installed shortly

after movement began, showed the location of the active and

passive failure surfaces.

The State immediately installed horizontal drains to lower the

water level and temporarily stabilize the movement. Analysis of

the structural condition of the wall disclosed no major planes of

weakness. A lateral earth pressure analysis disclosed that

additional lateral assistance was required to establish an

adequate minimum safety factor of 1.5 against future sliding. The

method chosen for wall repair could neither disturb the ground

behind the wall nor infringe on the safe clearance distance to the

I-95 pavement. The Interstate Division of Baltimore City, which

had responsibility for design, selected a permanent anchor repair

solution.

The stability of each wall panel was determined by lateral earth

pressure analysis for the worst hydrostatic condition. From this

analysis, the additional amount of resisting force was computed

for each panel to ensure a 1.5 safety factor. The soil conditions

behind the wall indicated that the anchors could safely develop a

design capacity of 50 tons. The number of anchors per panel was

determined by dividing the total additional required resistance in

each panel by the design anchor load of 50 tons and rounding it

off to the next whole number. The anchors were located at the

required resultant pressure point on each panel.

The specification for the permanent anchors contained a prequalification clause to ensure that only an experienced permanent

anchor contractor was permitted to bid the work.

The performance-type specification also allowed the contractor to

choose the most appropriate anchor tme I dimensions, and

installation procedure to achieve the required design load. A

patented anchor type known as TMD was selected by the contractor

as the best method to achieve the design load in the project soils

(see Figure 4C).

The TMD anchor has a substantial advantage over the other anchor

types installed in cohesive soils in that several stages of

grouting and regrouting can be performed in each anchor to develop

he required capacity. High pressure grouting in cohesive soils

must be done with care as application of excessive pressures will

fail the clay surrounding the bond zone, resulting in very low

anchor capacities.

desired

All 98 anchors on this project achieved the

test capacity and were accepted (see Figure 4D). After

lockoff, all anchor heads were encapsulated with plastic, greased13

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filled caps to prevent corrosion (see Figure 4E). The FHWA-DPD

funded monitoring equipment for the wall to assess long-term

performance of the permanent anchor solution. The final report,

which is included in the appendix, indicates that wall movement

has stabilized and the anchors are performing successfully.

The benefits of performance-type specifications containing a prequalification statement were shown on this project. The work was

professionally and cost effectively completed within the allotted

time frame. The Interstate Division of Baltimore City project

engineer could not remember a project where better relations

existed between the contractor and the State.

In December 1981, a Cooperative Agreement was signed with Maryland

DOT to document wall behavior. The performance monitoring and

reporting for the permanent anchor wall instrumentation were done

by the Schnabel Foundation Company with Messrs. David Weatherby

and Harold Ludwig as co-principal investigators. The installation

and monitoring of slope movement and water levels at the wall site

were handled for Maryland DOT by Messrs. Paul Wardenfelt of the

Interstate Division of Baltimore City and David Martin of the

Bureau of Soils and Foundations, as co-principal investigators.

The data obtained from this instrumentation was significant in

several aspects. The major concern for using anchors at this site

was the presence of fine grained soils in the anchor bond zone.

The anchor instrumentation verified that these soils could safely

withstand the required anchor loads without deflection. However,

the selection of the proper anchor type played a significant role

in obtaining the necessary capacity. The performance

specification permitted the contractor to select the anchor type

best suited to the site soil conditions and load requirements.

The TMD regroutable anchor which was selected proved to be both

the optimum anchor type for the site and of such a configuration

that instrumentation could be reliably installed.

Later, in preparation of a generic anchor specification, FHWA

would recognize that the anchor contractor was the most

knowledgeable to select the best anchor type for the project

conditions.

The analysis of the data from the project instrumentation showed a

gradual transfer of load from the front of the bond zone to the

middle and rear third of the bond length. Also, a short section

of the grout column in front of the load zone was observed to

transfer load to the soil. This pointed out the need to both

begin the bond zone at an offset distance behind the assumed

failure surface and to require weak grout in the free stressing

length.

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Long-term measurements of the deflection of the wall face indicate

only minor movements have occurred with the net effect that the

wall has moved into the slope. This may be indicative of

conservatism in estimating the required force to stabilize the

original wall instability.

The instrumentation system employed for these anchors was the most

reliable of all the demonstration projects. A few general

observations on the success of the instrumentation are:

0 The instruments were selected and installed by a

specialist instrumentation contractor.

o Although strand tendons were to be used in production

anchors, bar tendons were used in instrumented anchors

to optimize instrumentation reliability.

0 Duplicate instrumentation was placed on the bar tendon

and TMD external tube to insure reliable data

collection.

Pre-desiqn Test Anchor Proqram

I-90, Seattle, Washinqton

During the preliminary design phase of I-90 in Seattle,

Washington, a review was made of the preliminary designs to

support high cut slopes along the proposed alignment. A

preliminary cost-estimate of $24 million had been made for

cylinder pile walls to retain these cuts. An alternate design

using permanent ground anchored walls estimated at $6 million had

been suggested, but concern existed about long-term anchor

capacity in the clay subsoils. To evaluate long-term performance,

a pre-design $150,000 test anchor program was proposed. The

program was developed to establish design criteria and

construction control procedures which would insure long-term

anchor support in the project soils. In June 1983, a Cooperative

Agreement was signed between the Demonstration Projects Division

and Washington State to provide $50,000 in funds for

instrumentation of, and reporting on, test anchors installed in

the over-consolidated clay deposit at the project site.

Washington State designated Mr. Robert Josephson as principal

investigator and selected Mr. Garry Horvitz of Hart-Crowser and

Associates to be the co-principal investigator. The test anchor

site is shown in Figures SA-5D.

The test anchor program was designed to use anchor types and

installation procedures which were common to permanent anchor

construction in the Northwest. For that reason, a 12-inch

diameter, non-pressure grouted anchor was selected, although it

was generally agreed that higher pressure, regroutable anchors

would provide higher capacities at shorter lengths. Bar tendons

were used to facilitate instrumentation, although multiple bars

needed to be installed in the anchors which were tested to pullout

to insure tendon failure did not occur prior to soil bond failure.

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The testing procedure was directed at establishing the

relationship between anchor load and creep. Short bond lengths

would be used to permit determination of ultimate capacity with

reasonably sized test equipment. Although temporary anchors in

these over-consolidated clays had been loaded to high values, it

was suspected that design loads based on short term pullout tests

would be subject to excessive long-term movement. The basic test

procedure chosen was as described in detail in FHWA RD 81/150,

which is based on the French Standards for permanent anchors. The

end result of these tests is to determine the "critical creep

tension," i.e., load beyond which unacceptable creep occurs.

The testing confirmed the suspicion that the critical creep

tension would be substantially less than the ultimate load

measured on the pullout test. In fact, the critical creep tension

was one half of the ultimate load. Based on these results, the

ultimate bond stress between the grout bulb and the clay was

estimated and used to determine that the desired design load could

be achieved in a reasonable bond length. The test anchors were

locked off at various percentages of the critical creep tension

and monitored for several years. The results of the monitoring

were that only minimal long-term creep was observed.

Several permanently anchored walls have been completed on I-90

based on the results of this study. These walls are all

performing satisfactorily with no evidence of movement or

distress. Short-term testing procedures developed in the predesign anchor test program were used in construction to verify the

long-term capacity of anchors on the I-90 project.

In summary, the use of a $150,000 test anchor program by the

Washington DOT resulted in a savings of $18 million on I-90 as

well as providing valuable information for private projects, which

have since been designed for permanent anchors in the overconsolidated clays in Seattle.

Correction of Landslide

KY-227, Carroll County, Kentuckv

In 1983, the Geotechnical Section of the Division of Materials,

Kentucky Department of Highways, was involved in the design of a

landslide stabilization on KY-227. The landslide, which had been

active for several years, affected about 400 linear feet of

roadway. Solutions to the problem were limited as the roadway

location was bounded by a marginally stable, uphill slope and a

railroad located downhill from the road. The 25-foot depth to the

slide surface ruled out shear key construction or removal of poor

materials while the use of horizontal drains only increased the

safety factor to 1.1. The application was well suited for a

permanent ground anchor solution, but the Department had not

designed and let a permanent anchor project at that time. The

Department was concerned about employing this new technology at a

site where an on-going landslide required permanent stabilization

in a short time period.

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The solution was to adopt a shared responsibility design-construct

approach to a permanent ground anchor design. The Department's

geotechnical engineers progressed borings, performed lab tests,

selected soil strength values, and performed stability analyses to

determine the resisting forces required to stabilize the

landslide. A unique specification was developed to permit

alternate permanent ground anchor solutions to be designed by

qualified anchor firms. Specific experience requirements were

listed for the anchor design firms. Interested firms were

required to submit detailed designs to the Department for approval

within a given time-frame before the project was bid. The

Department provided a package of geotechnical information, the

resultant force to be resisted by the anchor wall, and specific

structural design requirements for the anchor wall design. The

submitted designs were required to include complete design

calculations, detailed construction drawings, and any special

notes or specifications needed to supplement the Department's

submittal. Each firm's calculations were to be presented clearly

so that engineers unfamiliar with permanent anchor walls could

review the information in a short time.

The Department formed an internal review board consisting of

structural, geotechnical, and construction engineers to study the

submitted designs. These initial reviews were very time

consuming, particularly because different anchor firms used

different design methods to achieve a final anchor wall system to

resist the given force.

The board realized that the original design criteria supplied to

the contractors needed to be clarified to permit all alternate

designs to be prepared on a common basis. Items such as the

design pressure diagram to be resisted, the use of wall friction

in the soldier pile design, drainage requirements, and the design

procedure for wood logging were redefined. The specialty

contractors were requested to revise their original designs and

re-submit. The re-submitted designs were reviewed by the board in

a short period of time and the project let on schedule. Although

certain other deficiencies in the construction specifications were

found after contract award, the project proceeded smoothly to

completion.

Kentucky benefited from their contracting approach to this project

in several ways. One, they did not possess the in-house expertise

to design a permanent anchor wall before this project. The prebid

design approach permitted exposure to several different wall

concepts and design philosophies. After completion of another

similar permanent anchor wall by the prebid method, Kentucky

believes sufficient in-house design knowledge exists to permit

assumption of some design details and use of a performance

specification which would permit post bid alternates.

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Secondly, the use of a pre-qualification requirement for the

permanent anchor design and construction insured that only

experienced permanent anchor specialty firms would be eligible for

this work. This minimized the amount of construction inspection

necessary to obtain a quality product. Kentucky inspectors were

able to observe the specialist contractor's methods, quality

control procedures, and equipment in order to develop confident

inspection techniques for future projects.

Thirdly, the prebid specification is a good vehicle to implement

the cost-effective technology of permanent anchoring on public

projects. The agency establishes the basic design framework and

permits several experienced contractors to compete for the most

cost-effective design.

The Carroll County wall (and a subsequent anchored wall in

Campbell County) has been a successful use of permanent anchors to

stabilize a landslide. The instrumentation indicated that by

November 1985, movement of the wall and highway had virtually

stopped.

An inspection of the completed permanent anchor wall by the FHWA

project manager on October 15, 1987, indicated that the roadway

behind the wall was stable. No evidence of any movement was

observed in the roadway or guardrail (see Figures 6A-6C).

However, two problems affecting durability of the wall face were

observed. Termite infestation was observed in a few of the

treated wood lagging sections, which comprise of the final wall

face (see Figure 6D). Similar problems have been reported on

other permanent walls faced with treated wood. It is postulated

that the wood lags develop cracks during initial stressing of the

anchors to the test load; i.e., commonly 1.33 to 1.50 of the

design load. In fact, random lags may actually be subjected to

higher stresses as distribution of load is not uniform across the

wall face due to the unevenness of the soil cut face on which the

lag bears. These cracks extend through the treated skin and into

the untreated wood core which is eventually attacked by the

termites. Highway agencies should carefully assess the use of

wood lagging as the permanent, load-bearing face for permanent

anchor walls, particularly in locations where routine inspection

and maintenance are not feasible.

The inspection also disclosed that the "Tapecoat TC Mastic," used

as protective coatings on exposed steel surfaces, was blistering

and peeling. Corrosion of the waler was observed beneath the

peeled coating (see Figure 6E).

Lateral Support of Bridqe End Slopes

Dimond Boulevard - Anchoraqe, Alaska

In 1985, a Cooperative Agreement was executed with the Alaska

Department of Transportation to provide funds

the

for instrumenting

agency's first permanent ground anchor

18

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installation. The project involved construction of an anchored

wall to support the existing end fills and abutments on the Dimond

Boulevard project in Anchorage. Traffic would be maintained on

the existing structure during construction. These walls were

unique in that resistance had to be provided for both vertical and

lateral loads from the abutments which were supported on spread

footings located above the wall in the end fill. The walls were

required because the under road, Dimond Boulevard, was being

widened and lowered to provide increased clearance under the

existing structure. The principal investigator was Mr. Thomas

Moses of Alaska DOT.

Installation of soldier piles beneath existing

problems,

structures poses

particularly when

than the available

the pile length required is greater

clearance. The solution used for

installation

pile

was to close one lane to traffic on the existing

bridge, drill holes in the deck between girders, and install the

piles through the deck to the designed embedment into the ground.

After completion of the pile installation in one lane, the piles

are cut off below deck level, the holes sealed, and traffic

restored in that lane while the operation begins in the next lane.

The total time for installation of all piles was less than 1 week

using this method.

One unexpected problem about these holes arose during construction

when an extremely heavy rain occurred. The drainage from the deck

entered a few open holes and poured down on one end slope

erosion and

causing

settlement of one abutment. A solution to this

problem is to require deck holes to be temporarily sealed against

water infiltration immediately after drilling and permanently

sealed immediately after the soldier beam is installed.

The anchors were installed into

fill at levels

the existing granular approach

below the existing abutment footing.

vertical and horizontal clearance existed for the anchor

Adequate

operation such that traffic

drilling

could be maintained on Dimond

Boulevard when required during the construction.

Although the final report for this project has not been submitted,

observations made for a year after the construction indicate the

anchored wall is functioning as designed (see Figure 7). It does

appear that the wall moved into the backslope a small amount which

caused a decrease in the lockoff load on the tendons. The reasons

for this movement and decrease in load may be better known when

the final report is received in 1990.

Urban Railroad Grade Separation

North Street Project, Lima, Ohio

The North Street project, which is located in an old, congested

area of downtown Lima, Ohio, was

anchor project. The project

the State's first permanent

requiring

right-of-way was very limited,

underpinning of adjacent structures (see Figures 8A-8C)

19

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as part of the permanent anchor wall construction. Only small

wall movements could be tolerated due to the proximity of the

structures to the wall. In addition, the bond zone soils were

predominately fine-grained with respective liquid limits and

plastic indices generally above 30 and 15. These soils are at the

lower end of soil types which are considered suitable for

permanent ground anchors.

In late 1985, a Cooperative Agreement was executed between FHWA

and the State of Ohio to provide funds for monitoring the

performance of permanent anchors on this project. The coprincipal investigators were Mr. Richard Engel of Ohio DOT and

Mr. Mark Lockwood of the H. C. Nutting Company, consultants for

this project.

The project construction specifications were developed on a

performance basis and required that a permanent anchor specialty

contractor construct the anchored wall. All anchors were required

to be tested before lockoff with payment to the contractor based

on acceptance criteria for the tests. This specification became a

critical factor in the success of the project as the Ohio DOT

construction engineers had no experience with inspection of

permanent anchor wall construction. The specialty contractor who

was the successful bidder, Schnabel Foundation Company, made every

effort to explain the proper construction procedures and assist in

training the project inspectors. Project inspectors photographed

numerous steps in the wall construction to provide training

materials for inspectors on future anchor projects. Although this

project was difficult in terms of both surface and subsurface

problems, the construction proceeded smoothly and without incident

to completion.

This project, more than any other, demonstrated the value of both

pre-qualification of specialty contractors, and the use of

performance type specifications for permanent anchor work. A

major objective of the instrumentation was to determine the

movements and loads transferred to the soldier piles as successive

levels of anchors were stressed. The data, available at the end

of construction, indicated that the vertical load on the soldier

pile increased rapidly as the excavation proceeded to grade and as

each successive row of anchors was stressed. Of the 59 kips

estimated in design to be the maximum vertical load, 55.4 kips

were transferred below grade. This

little load transfer above

initial data suggests very

grade between the soldier pile back

face and the soil face being supported. This tends to confirm the

conservative design approach of selecting an angle of wall

friction of zero when calculating earth pressures against

permanent anchor walls.

A second interesting observation was the decrease in load carried

by the first level of anchors when the second level was tensioned.

This indicates the need in design to check the construction

situations where the first anchor level has been installed and

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excavation has proceeded to below the second anchor level. In

some cases, this stage will produce the maximum load to which the

level one anchors will be subjected.

Two other points of interest are the relatively large cyclic

movements in both north-south wall deflection and the temperature

range noted 15 feet behind the wall. Movements of 0.2 inches

appear to have occurred in channel number 93 between winter and

summer. Detailed temperature measurements of the soil both behind

the wall and in the anchor bond length were taken.

The detailed report in the appendix contains figures which are

updated to show nearly 1 year of readings, although the text only

contains preliminary comments on the period up to about 3 months

after construction. The final report on this project is not due

until December 1990. Figures 8D-8H show anchor installation and

the completed wall.

Tieback Bridse Abutment

Ramp Q, I-279, Pittsburgh, Pennsvlvania

In late 1987, PennDot entered into a Cooperative Agreement with

FHYWA to instrument and monitor the performance of a tied back

bridge abutment in Pittsburgh, Pennsylvania. This is only the

second major application of constructing a permanent anchored

bridge abutment in the United States. The reason for the design

was potential lateral instability of the slope on which the

abutment would be constructed.

this study is Mr. James Withiam of

The principal investigator for

D'Appolonia, consultants for

this project.

At the writing of this report, the abutment construction has been

successfully completed but no conclusions have been developed

regarding performance of permanent anchors.

V. REHABILITATION OF STRUCTURES WITH PERM2XNENT GROUND ANCHORS

During the progression of the permanent anchor project, the most

cost-effective application of the technology was in rehabilitation

of structures. Permanent anchor designs for rehabilitation

projects were relatively straight forward and accomplished within

a short time.

The equipment

small,

required for permanent anchor work is relatively

readily available nationally, and

materials

easily mobilized. The

are common construction items available nationally in a

short time frame.

rehabilitation

All these factors point to anchor use for

work, particularly when the project repair must be

accomplished in a short time frame.

The following two projects are examples of walls for which the

demonstration project manager provided technical assistance to

achieve fast, cost-effective repair.

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Hope, Idaho, Cemetery Wall Rehabilitation

A 34-foot high by 200-foot long retaining wall was built in 1975

to preserve a pioneer cemetery located above the proposed grade

just west of Hope, Idaho. The wall was designed with a flexible

face of precast reinforced concrete segments (stretchers)

interconnected by vertical steel rods. Lateral support of the

flexible panels was achieved in the lower 12 feet with rock bolt

tiebacks, in the middle 8 feet by gravity wall design, and the

upper 14 feet by deadman anchors. Following construction, the

stretchers began to crack and spa11 and the face began to tilt. A

study of wall conditions in 1978-79 concluded that interaction of

the vertical rods and reinforcing steel of the stretchers was

causing the reinforcing steel to break out of the stretchers in

the lower 12 feet of the wall (see Figures 9A-9B).

It was recommended that the wall be strengthened in this section

and that long-term corrosion of unprotected steel wall elements be

considered in the rehabilitation.

The FHWA Western District Federal Division was assigned

responsibility for the wall repair. The remedial treatment had to

accomplish several objectives:

0 not distress the delicate structural stability of the

existing wall or disturb the cemetery,

0 maintain a safe minimum clearance distance from the

highway,

o provide long-term corrosion resistance,

o be cost-effective.

Fortunately, subsurface conditions at the site were adequately

defined by the site geology and records of the existing rock bolt

installation. The subsurface conditions consisted of a mixture of

sand, silt, and rock fragments overlying rock at relatively

shallow depths. Concerns for long-term corrosion and the need to

reinforce the existing wall with minimal disruption to the site,

combined with favorable subsurface conditions, led to a permanent

ground anchor solution.

The permanent anchor design was complicated by the delicate

condition of the existing wall face. Normally, the anchors would

be drilled through the wall and then stressed against the existing

wall face to above design load. However, the thin wall face could

not withstand any concentrated load. The available clearance to

the adjacent roadway allowed placement of a 16-inch thick

reinforced concrete face over the bottom 12 feet of the existing

face. Although this thickness was adequate to distribute the

anchor design load over the face area, test stressing the anchors

to above design load on this new face was not deemed prudent.

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Since the wall length was short, an alternate testing procedure

was used whereby two pre-production anchors would be performance

tested to over 200 percent of design load against the natural

ground just beyond the ends of the wall. After successful tests

were performed, the contractor was required to install the

production anchors with the same materials and procedures used for

the pre-production testing. Drainage that was occurring through

the existing gapped wall face was designed to be carried by pipes

placed through the new solid wall face (see Figures 9C-9E).

The production anchors were bid on a "per-ft-of-anchor-installed"

basis rather than the more common per-anchor basis because it was

impossible to proof test each installed anchor. It was also

necessary for the designer in this case to assume full

responsibility for establishing a guaranteed "safe" anchor.

Therefore, the anchor hole diameter, grout pressure, drilling

procedure, free length, and bond length were specified in the

plans. Normally, the contractor would bid on a per-anchor basis;

determine all anchor dimensions except minimum, free, and bond

lengths; and prove the design load could safely be held by testing

each anchor. In this project, the production anchors were

stressed to a 25-kip lockoff load. The measured movement of all

anchors at that load was within the acceptable limits established

from the pre-production test anchors.

The contract time for construction was 90 days, which would have

been met except for some unexpected weather conditions. The two

pre-production performance test anchors were installed at a bid

price of $1,500 each. The approximately 1,900 feet of production

drilling and grouting was completed for the 61 wall anchors, which

were double corrosion-protected l-inch diameter bars. The bid

price per linear foot of production anchor was $30 versus an

estimated actual cost per foot of $25 by the contractor.

Based on the success of this project, it appears that permanent

anchors can be successfully used as an alternate method of repair

for other thin-faced walls such as metal bin or concrete cribbing.

Nevada, Carlin Canyon Portal Rehabilitation

The portal walls of the Interstate 80 Carlin Canyon Tunnel in

Nevada were built in the 197Os, using a unique lateral support

system. Galvanized steel tie rods were fixed into the concrete

wall face and extended back to anchors in the nearby rock

These

slope.

rods were designed to resist the lateral pressure generated

by the backfill that was subsequently placed. However, after

8 years of service, one of the portal walls began to move outward

at an excessive rate. To stop this movement, the State removed

the backfill from the failing wall sections. The tie rods that

were unearthed during backfill removal failed due to severe

corrosion, particularly near the wall-rod interface. A closer

examination showed active corrosion on all parts of the galvanized

rods. As conditions were similar behind all other wall panels,

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DP68 - final report

any remedial design selected would have to apply to all panels.

The choices were to reconstruct the walls or re-establish

permanent lateral support for the existing walls. The State DOT

selected permanent anchors to provide the required lateral support

to the existing walls.

Two problems were overcome in the permanent anchor design. First,

the thickness of the existing wall was inadequate to support and

distribute the required permanent anchor loads (45 to 70 tons per

anchor). This problem was resolved by casting vertical concrete

beams at specified center-to-center distances along the panels.

The 1 3/8-inch diameter single-corrosion-protected bar anchors

were placed through and stressed against the beams, which were

adequately reinforced to sustain the stressing load and distribute

the force over the panel height. The second problem only occurred

at panels where the backfill had been removed. Permanent anchors

are normally post-tensioned to the required proof load after

installation. However, passive resistance behind the excavated

panels was insufficient to allow stressing the anchors to the test

loads without damaging the wall. In addition, backfill should not

be placed and compacted around anchors that have previously been

installed. Backfill compaction operations can damage the

corrosion protection of the permanent anchor and can cause bending

of the tendon free length under the compactive load. Such a

backfill procedure was used in the original portal construction

and reportedly caused inward wall deflections due to bending of

the rods.

To prevent these problems, the State required backfill to be

placed in stages and compacted behind those wall panels to about

3 feet above each successive row of anchors. The anchors in each

lower row were stressed and locked off before the backfill was

placed to the next higher row. No attempt was made to pull the

deflected wall back to its original position for fear of

structurally damaging the panels. Drainage was reestablished

behind the excavated panels by handing vertical drains down the

back face and connecting them to a positive outlet before

backfilling.

The specification for the anchors was performance based; i.e., a

pre-qualification statement was included to ensure the work was

awarded only to an experienced permanent anchor contractor. The

contractor was responsible for determining the actual required

anchor bond length to develop adequate load capacity to satisfy

anchor testing requirements for the design loads on the plans.

Within the specification, the contractor was allowed to use his

expertise to determine tendon type f drilling method, grouting

pressures, multiple grouting techniques, and bond length

variations to produce the most cost-effective anchor. The State

accepted or rejected each anchor on the results of either

performance or proof tests that were done on the installed

anchors. The 64 anchors were bid on a per-unit basis at an

average cost of $2,800, which included labor, materials, drilling,

stressing, and testing. The actual anchor work was completed

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within 3 months. The entire project, from design through

construction, took about 18 months. The final wall is shown in

Figures 10A and 10B.

VI. CONCLUSION

The objective of Demonstration Project No. 68 was to introduce,

nationally, the concept of permanent ground anchor use into

routine construction practice. This objective has been

accomplished through a multi-dimension program of research,

technology transfer, technical assistance, and interaction with

both public and private organizations involved in permanent

anchoring. As documented in the text of this report, the volume

of permanent anchor work in the United States is multiplying

yearly. State highway agencies are now considering anchors as

routine alternatives to conventional techniques rather than as

research objects.

Although the Demonstration Project has ended, the mechanism is in

place for further refinement and promotion of permanent anchor

technology. Organizations such as AASHTO, AHTBA, AGC, ASTM, and

the Post Tensioning Institute have on-going committees studying

permanent ground anchor standards and applications. Furthermore,

FHWA and other government organizations are advancing programs for

research to optimize the design procedures now in common use.

25

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HAWAII

Figure 1. Demonstration Presentations Completed

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b3tective hotective plastic Cap end Nut

Anti-corrosion Grease

Figure 2 Simple Schematic of a Pemranent Anchor

A-2

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Figure 3. --Georgia f-75 Project 

3A.--:Pesting 0: I'irst Anchor ROW 

3B.--Forming Concrete Wall Face Over Anchors 

A-3 

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Figure 3 .--Georgia I-75 Project (con.) 

3C.--Final Wall, 1984 

:, 

_ 

3D.--Wall, 1988 

A-4 

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Figure 3 .--Georgia I-75 Project (con.) 

3E.--Stable Roadway, 1988 

Above Wall - No Pavement Cracks 

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Figure 4 .--Maryland I-95 Project 

Figure 4A.--Wall Joint Spalling, 1980 

4B.--Wall Base Translation, 1980 

A-6 

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Figure 4 .--Maryland I-95 Project (con.) 

4c .--TMD Anchors Installed, 1981 

4D .--Anchor Testing 

A-l 

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Figure 4.--Maryland I-95 Project (con.) 

Figure 4E.--Final Wall, 1984 

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Figure 5 .--Washington I-90 Project 

., S*’ 

(’ 

_ ..‘. 

# 

/ 

I 

‘. 

I 

Figures 5A and SB 

Anchors Installed Through Existing Cylinder Pile Wall 

A-9 

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Figures 5C and 5D 

Instrumentation for Anchor Testing 

A-10 

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Figure 6 .--Kentucky Route 227 Project: 

Figure 6A 

Embankment Stable With No Evidence of 

Movement 3 Years After Construction 

A-11 

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Figure 6 .--Kentucky Route 227 Project (can.) 

Figure6 6B and 6C 

Views of Wall Face 4 Years After Construction 

A-12 

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Figure 6 .--Kentucky Route 227 Project (con.) 

Figure 6D 

Termite Infestation of Permanent Treated Wood Face 

Figure 6E 

Blistering and Peeling of Protective Coating on Waler 

B-13 

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Figure 7 .--Alaska Dimond Boulevard Project 

Completed Dimond Boulevard Wall 

A-14 

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Figure 8 .--Ohio Lima Project 

Figures 8A, 8B, and 8C.--Building Underpinning Operations 

A-15 

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Figure 8 .--Ohio Lima Project (con.) 

I / c - . . F II - :x , 

Figures 8D and 8E .--Anchor Drilling 

A-16 

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Figure 8 .--Ohio Lima Project (con.) 

OF.--First Level Anchors Installed 

A-17 

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Figure 8 .--Ohio Lima Project (con.) 

Figures 8G and 8H 

Opposing Views of Completed Walls, 1989 

A-18 

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Figure 9A.--Hope Wall Condition, 1980 

Figure 9B .--Closeup of Crack in Lower 12 Feet of Wall 

A-19 

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Figure 9 .--Idaho Hope Project (con.) 

Figure 9C.--New Reinforced Fascia Wall 

Poured Prior to Anchor Installation 

9D.--Completed Anchored Wall Repair, 1981 

A-20 

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Figure 9 .--Idaho Rope Project (con.) 

Figure 9E.-- Note Small Thickness of Wall Repair 

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Figure 10 .--Nevada Carlin Canyon Project 

Figure lOA.--Completed West Portal, Carlin Canyon Tunnel 

Vertical Beams Contain Anchors 

Figure lOB.--Completed East Portal, C'arlin Canyon Tunnel 

A-22 

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