computer program for simulation of wall construction sequence

8/16/2019 Computer Program for Simulation of Wall Construction Sequence

1/90

us

Army

Corps

o f

Engineers©

Engineer

Research

and

Development Center

Computer-Aided

Structural

Engineering

Project

User's

Guide:

ompute r

Program

fo r

Simulation

o f

Construct ion

Sequence

fo r Stiff Wall Systems with

Multiple Levels

o f

Anchors (CMULTIANC)

William

P .

Dawkins,

Ralph

W.

Strom,

Robert

M .

Ebeling

August

2003

Approved for public

release;

distribution

is

unlimited.


2/90

Computer-A ided

Structural

RDC/iTL SR-03-1

Eng ineer ing Project

ugust

2003

User's

Guide:

omputer

Program

fo r

Simulation

o f

Construction

Sequence

fo r

Stiff Wall Systems

with IVIultiple

Levels

o f

Anchors (CMULTIANC)

William P .

Dawkins

5818

Benning

Drive

Houston,

TX

7096

Ralph

W.

Strom

9474

S.

E.

Carnaby W ay

Portland,

OR 7266

Robert M .

Ebeling

Information

Technology

Laboratory

U.S.

Army

Engineer

Research an d

Development

Center

3909

Halls

Ferry Road

Vicksburg,

M S

9180-6199

Final

report

Approved for

public release;

distribution

is

unlimited

Prepared

for

U.S.

Army

Corps

of

Engineers

Washington,

DC

20314-1000

Under

ork

Unit

31589


3/90

AB S T RACT :

his report describes th e PC-based

computer

program C M U L T I A N C , used to evaluate th e

effects

of staged

construction

activities i.e.,

xcavation

nd

tieback

post-tensioning)

on

wall

nd

oil

behavior. T he

C M U L T I A N C simplified

construction sequencing

analysis is applicable

to

stiff walls with a

single ro w or multiple rows of post-tensioned tieback anchors. Top-down construction is assumed in this

analysis procedure.

T he

retaining

wall

system

is

modeled using

beam

on

inelastic

foundation

methods

with

elastoplastic

soil-

pressure

deformation

urves R -y

urves)

used o

epresent

he

oil

behavior.

T he R -y

urves

re

developed

within

th e

C M U L T I A N C

program

in

accordance

with th e reference deflection

method.

T he

retaining

wall

is

analyzed

on a

per-unit

length ru n ofwall basis.

One-dimensional

finite

elements

ar e

used

to

model th e retaining wall with closely spaced inelastic concentrated springs

to

represent soil-to-structure

interactions on

both

sides of th e wall. Discrete concentrated, elastoplastic springs ar e used

to

represent th e

anchors.

For each

evel

of excavation (associated

with a

particular

tieback installation) C M U L T I A N C

performs

three

equential

nalyses:

a)

taged xcavation

nalysis to

he

xcavation

evel

needed

or

nchor

installation)

to

capture soil loading effects,

(b )

R -y curve shifting

to

capture plastic soil movement effects,

and

(c )

tieback

installation

analysis

to

capture

tieback

anchor

prestressing

effects.

R -y

curves

are

shifted

to capture th e plastic movement that takes place

in th e

soils

as th e wall displaces toward th e excavation

fo r

those conditions

where

actual wall

computed displacements

exceed

active

computed displacements.

R -y curve hifting s necessary

to

properly apture oi l eloading effects s tieback nchors re post-

tensioned

and th e wall

is

pulled

back

into

th e

retained

soil.

D I S C L A I M E R :

h e contents

of

this report

are

not

to

b e

used

fo r

advert i s ing, publ ica t ion, or promot iona l pu rposes .

Citat ion

of

t rade

n a m e s

does n ot constitute

an

official

endorsement or approval of th e use of such c ommerc i a l products .

A ll

product

n a m e s

an d t rademarks

cited

are

th e property of

thei r respect ive

o wn e rs . h e f ind ings

of this report are

n o t

to b e construed as an

official

Depa r tment of th e A r m y posi t ion unless so designated by oth e r authorized

d o cume n t s .


4/90

Contents

C o n v er s io n Factors , Non-SI to

SI Unit s

of

M e as u re m e nt v ii

Preface

ii

1—Background o n T i e b ack Retaining

Wall

Systems

1.1

es ign

of

Flexible

Tieback Wall

Systems. . . . . .

1.2

De s i gn

of

Stiff

Tieback

Wall

Systems

1.2.1

dent i fy ing

stiff w al l

sys tems

1.2.2 Tieback w al l pe r fo rm ance

object ives

1.2.3

rogress ive

des ign

of t i eback w al l

sys tems

1.3

IGID

Method

1.4 R I G I D

2

M e t h o d 0

1.5 W IN K L E R M e t h o d 0

1.6

W IN K L E R

2

M e t h od

1.7

NLFEM M e t h od 2

1.8 Factors

Affect ing

Analys is M e t h o d s

an d

Resul t s

2

1.8.1 verexcavat ion

2

1.8.2

round

anch or

pre loading

3

1.9

Cons t ruct ion

Lo n g - T er m ,

Cons t ruct ion

Shor t -Term,

an d

Pos tcons t ruct ion

Condi t ions

3

1.10

ons t ruct ion-Sequencing

An a l y ses 4

2 — C o m p u t e r

Program C M U L T I A N C 6

2.1 nt roduct ion

6

2 .2 Discla imer

6

2.3

ystem

Overview

6

2 .4 A nch ors ̂

2 .5 xcavat ion

Elevat ions

7

2 .6 o il Profi le

8

2.6.1

n it weights

8

2.6 .2

t rength

proper t i es

8

2 .7

Water

8

2 .8 Vertical

Surcharge

Lo a d s 9

2 .9 Limi t ing

Soil

an d

Water

Pressures 9

2.10 Calcu lat ion

Points 9

2.11 ctive and Pass ive

Pressures

0

2.11.1 ndrained

( cohes ive)

soils 0

2.11.2

Dra i ne d

( cohes ion less)

soils

0

2.11.3 ressure

coefficients 0

III


5/90

2.11.4

Profiles

with

interspersed

undra ined

and

dra ined

layers 2

2.11.5 ressures

d ue

to

surcharge

loads

2

2.12 Water

Pressures

2

2.13 Nonlinear Soil

an d

A n c h o r

Spr ings

2

2.14

Displacements

at Limit ing Forces 4

2.15

hifted

Soil

Spring

Curves

5

2.16

A n c h o r Spr ings 5

2.17

Finite

Element

M o d e l

8

2.17.1

ypica l

e l em en t 8

2.17.2

ypica l

n o d e

9

2.18 xterna l

Suppor t s

9

2.19 M e t h o d

of

Solut ion 9

2 .20

tabil i ty

of

Solut ion 0

2.21

om pu t e r Program

0

2 .22

n p u t D a t a Files

1

2.23 utpu t Dat a File

'

^3 1

2 .24

Graphics

2

2.25

onstruction

Sequence

Simula t ion

2

2.25 .1 npu t

data

2

2 .25 .2 tage

1 : nitial

cond i t ions

2

2.25 .3

tage 2 :

olut ion

fo r

init ial

cond i t ions

3

2 .25 .4 tage

3: hift

of SSI

curves

. 33

2 .25 .5

tage

4:

olut ion

w ^ i t h

shif ted

SSI

curves 3

2 .25 .6 tage

5: o p

a n c ho r instal lat ion 3

2 .25 .7 tage

6: xcavat ion

3

2 .25 .8 ubsequent stages 3

2 .26

Unit s

a nd

Sign

C o n v en t io n s 4

3 — E x a m p l e

Solut ions 5

3. 1

nt roduct ion

5

3.2

ole tanche Wall

' ZZZ ''Z 35

3 .3

onnevi l le

T y p e Wall

1... .'... . 46

3 .4

CacoiloWall

.m.'. . .50

References 5

Ap p en d ix

A :

uide

fo r

D a t a Input l

A.l nt roduct ion l

A . 1.1

ource

of

input

l

A .

1.2

Dat a

edit ing

l

A.1.3

npu t

data file genera t ion

l

A .

1.4 ec t ions

of

input

l

A.l.5

redef ined

data

file 2

A .2

ead ing

3

A .3 Wall

S eg m en t

D a t a 3

A .4 Anchor Data

3

A .5

oil

Profile

D a t a

4

A .6

nit ial

Water

D a t a

6

A .7

Right -S ide

Surface

Surcharge

D a t a

6

A .8 xcavat ion Data

l

O

A .9 Wall

Bottom Condi t ions

l

1

I V


6/90

A.IO Terminat ion ll

A ppe nd i x B: bbreviated Input Guide l

SF298

List of F ig ures

Figure

1-1. Defini t ion of span

length

Z ,

Figure

2-1.

Schemat ic of

wall/soi l

sys tem

7

Figure

2-2 .

Log-spi ra l

pass ive

pressure

coefficients

(after

De par t m e n t

of th e

Navy

1982) 1

Figure

2-3. ressure

calculat ions

for surcharge

loads

3

Figure

2-4.

ater

pressures

4

Figure

2-5 .

onlinear

soil

spr ings 4

Figure

2-6 .

oncent rated

soil

spr ings

5

Figure

2-7 .

hifted

SSI soil

spr ings 6

Figure

2-8 .

onlinear a n c ho r spr ing 6

Figure

2-9 .

inite e l em en t

m o d e l 8

Figure

2-10.

ypica l e l em en t

8

Figure

2-11.

ypical

node

9

Figure

3-1.

ole tanche wa l l

5

Figure

3-2.

nput file

fo r

Soletanche

w al l 6

Figure

3-3.

choprint

of

input data

fo r

Soletanche wall 7

Figure

3-4 .

nit ial l imit

pressures

for Soletanche wall

8

Figure

3-5.

nit ial

SSI curves

for Soletanche wa l l

9

Figure

3-6.

esul ts for

init ial cond i t ions

for Soletanche

w al l

0

Figure

3-7.

hifted SSI

curves

for

Soletanche

wa l l

1

Figure

3

-8 . S u m m a r y

of

resul ts

after anchor lock-off

load

fo r

Soletanche

w al l 2

Figure

3-9.

S u m m a r y

of

resul ts

fo r anch or spring replacing lock-off

load fo r

Soletanche

wall 3

Figure

3-10.

Lim i t pressures

after

excavat ion

to eleva t ion

-30 fo r

Soletanche wa l l 4


7/90

Figure

3-11.

eft-side

SSI

curves after

excavat ion

to

eleva t ion

-30

fo r

Soletanche

wal l 4

Figure

3-12.

u m m a r y

of

resul ts

after excavat ion

to

elevat ion

-30 fo r

Soletanche wa l l 5

Figure 3-13.

a x im a s u m m a r y

fo r

Soletanche

wa l l

6

Figure

3-14.

onnevi l le

type wa l l

s imula t ion

6

Figure

3-15.

n p u t file

for

Bonnevil le

wa l l 7

Figure

3-16.

choprint

of

input data fo r Bonnevi l l e wal l

8

Figure

3-17. ax i m a

s u m m a r y

fo r

Bonnevi l l e

wal l

0

Figure

3-18 .

acoilowall 0

Figure

3-19.

n p u t file

fo r Cacoi lo wa l l

1

Figure 3-20 .

choprint

of

input

data

fo r

Cacoi lo

wa l l

2

Figure

3-21.

nit ial

water and

soil

l imit pressures fo r initial

cond i t ions

4

Figure

3 - 2 2 . ax i m a

s u m m a r y

fo r

Cacoi lo

wal l 5

List

o f

Tables

T a b l e

1-1.

Table

1-2.

Table

1-3.

T a b l e

1-4.

T a b l e

1-5.

Table

2-1.

T a b l e

2-2 .

Stiffness

Categor iza t ion

of

Focus Wall Systems

(Strom

and Ebel ing 2001)

Genera l

Stiffness Quantificat ion fo r

F o c u s

Wall

Systems

(Strom

and Ebel ing 2001)

D es ig n

and Analys is T o o l s for

Flexible

Wall

Systems

(Ebel ing

et

al . 2 0 0 2 )

D es ig n

an d Analys is T o o l s

fo r

Stiff

Wall Systems

(Strom and

Ebel ing 2 0 0 2 )

S u m m a r y of

R -y C u r v e

Const ruc t ion M e t h o d s

(Strom

and

Ebel ing 2001)

R ef e r en c e

Displacements 5

Unit s

and

Sign

C o n v en t io n s

4

V I


8/90

Convers ion Factors, Non-SI

to

SI Units o f

Measurement

Non-SI

units of

measurement

used

in

this

report

can be

converted

to

SI

units

using th e

following

factors.

Multiply By

To Obtain

feet

0.3048

meters

Inches

0.0254

meters

kip-feet

1,355.8181

newton-meters

kips

pe r

square foot

47.88026

kilopascals

pounds

(force)

4.448222

newtons

pounds (force) per square

foot

47.88026

pascals

pourids (force) pe r square inch

0.006894757

megapascals

pounds (mass)

0.4535924

kilograms

pounds (mass) per

cubic

foot

16.01846

kilograms

pe r cubic

meter

square

inches

0.00064516

square meters

tons

pe r

square foot

9,764.856

kilograms pe r square meter

VII


9/90

Preface

T hi s repor t descr ibes

th e

sof tware program

C M U L T I A N C ,

n ewl y developed

to

simulate

th e

simplif ied construction

sequence

m et ho d

of

analys is

of a stiff,

t ieback

wal l

with mult iple

levels

of prestressed

anchors

( a s su m in g t o p - d o wn

construct ion).

Funding fo r this

research

w as provided

by

th e C om pu t e r -A i d e d

Structural

Engineer ing

R esea r c h

Program

sponsored

b y

Headquar ters ,

U . S .

A r m y

C o r p s of

Engineers

( H QUS AC E ) ,

as

par t

of th e

Infrastructure

T e ch no l ogy

Research a nd

De v e l opm e nt

Program.

M s.

Y a zm in

Seda-Sanabr ia ,

Geotechnica l

and

Structures

Laboratory (GSL),

Vicksburg ,

M S, U.S.

A r m y

Engineer

R esea r c h

and De v e l opm e nt

C en t e r ( E R D C ) , w as

Program

M a n a g er .

T h e

s tudy

w as

conducted u nd e r Work Un i t 3 1 5 8 9 ,

C om pu t e r -A i d e d

Structural

Engineer ing

(CASE) , for whic h

D r.

R o b er t

L .

Hall, G S L , is

Prob lem

A re a Leader and

M r. Chris

Merril l ,

Chief ,

C o m p u t a t io n a l

Science

and

Engineer ing

Branch,

Informat ion

T e ch no l ogy

Laboratory

( ITL) ,

E R D C ,

is

Princ ipa l

Invest igator. T h e

H Q U S A C E T ec hn ic a l Monitor

is M s.

An j a n a

Chudgar ,

C E C W - E D .

T hi s

report w as

prepared

b y

D r.

Will iam

P.

D a wk in s ,

Houston ,

T X;

M r.

Ralph W. Strom,

Por t l and ,

O R ;

a n d

D r.

R o b er t

M .

Ebel ing,

Engineer ing

and

Informat ic

Systems

Divis ion

(EISD),

I T L .

D r. Ebel ing w as th e

au thor of

th e

scope

of

w o r k

fo r

this

research . T h e research

w a s conducted

u nd e r

th e direct

superv is ion

of D r.

Char les

R .

Welch,

Chief ,

EISD;

and D r. Jeffery

P.

Holland,

Direc tor ,

ITL.

C o m m a n d e r an d

Execut ive

Director

of

E R D C

w as

C O L John

W.

M o r r i s

III,

EN . Director

w as

D r.

J a m es

R .

Houston .

VIII


10/90

1

Background

on

Tieback

Retaining Wall Systems

T hi s report descr ibes th e personal com pu t e r ( P C )

-based com pu t e r program

C M U L T I A N C ,

used

to

simulate th e

s impl i f ied

cons t ruct ion

seq u en c e

m e t h od of

analys is

of

a

stiff t i eback

wal l .

T o p - d o w n

cons t ruct ion

is

a s su m ed in this analysis

procedure .

T h e

user's guide

to

C M U L T I A N C

is

given

in

C h ap t e r

2.

T hi s chapte r serves

as

an in t roduct ion to th e categorizat ion an d

analys i s of

flexible an d stiff t ie-

back retaining wall sys tems

involv ing

th e use

of

pres t ressed anchors .

T h e mul t i -

anch ore d

t i eback

earth

retaining

w al l sys tems

used

by

th e

U . S .

Army C o r p s

of

Engineers are classif ied

as

ei ther flexible or rigid accord ing

to

Strom an d

Ebeling

(2001,

2 0 0 2 )

and

Ebeling

e t al.

(2002) . T he

categorizat ion

of

a

t i eback

wall as

be ing

ei ther

f lexible

or rigid is used

fo r convenience in

de te rmining th e

appropria te

analys is

and/or

des ign

procedure

associated with

a

particular

type

(i.e.,

ca tegory)

of

wall .

1 .1

esign

of

Flexible

Tieback

W all

Systems

T h e

equivalent

beam

on

rigid

support

m e t h od

of

analys is

us ing

apparent

ear th-pressure

envelopes

is

m o s t often th e

des ign m e t h od

of

choice , primari ly

because of it s

ex p ed ien c y

in

th e

pract i cal des ign of

t i eback wa l l sys tems.

T hi s

m e t h od provides

th e

m o s t

rel iable

solut ion

for

flexible

w al l sys tems,

i.e.,

so ld ier

beam-lagging

sys tems

an d sheet-pile

wall

sys tems,

since

fo r

these types

of

sys tems

a

s ign if ican t

redis tribution

of

earth

pressures

occurs behind

th e wal l .

Soil

arching ,

s t ress ing of

g r o u n d anchors ,

cons t ruct ion-sequencing effects,

and

l agging

flexibility

a ll

cause

th e

earth pressures behind

f lexible wal l s

to

redis tribute to ,

an d

concent ra te

at,

anch or

suppor t

loca t ions

( F H W A- R D - 9 8 - 0 6 6 ) .

T hi s redis tribution ef fec t in f lexible

w al l

sys tems

canno t

b e

captured

by

equivalent beam on rigid suppor t

m et ho d s

o r by beam o n inelast ic foundat ion

analys is m et ho d s

w h e re th e

act ive

an d

pass ive

l imi t states

are

def ined

in

t e rms

of

R a n k in e

or

C o u l o m b

coefficients.

Full-scale

w al l

tes ts on

f lexible wall sys tems

( F H W A -R D-9 8 -0 6 6 )

ind ica ted

that th e act ive earth pressure used to

def ine

th e

minimxmi

load

assoc ia ted

with th e

so i l

springs

behind

th e

w al l

had

to

be

reduced

b y

5 0

percent

to

m a t c h

measured

behav ior .

Since

th e

apparen t

earth-pressure

d iagrams used

in

equivalent beam on rigid

support

analyses wer e

deve loped fi-om

measured loads ,

an d

thus

inc lude

th e

effects of soil arching ,

stressing of

g r o u n d

anchors ,

cons t ruct ion-sequencing

effects,

an d

l agging

f lexibil i ty ,

they

prov ide

a

Chapter

1 Background on Tieback Retaining Wall Systems


11/90

better

indicat ion

of

th e

strength

pe r fo rm ance

of

f lexible

t ieback

wal l

sys tems.

T hi s

is n ot th e

case fo r

*ftj5^wall

sys tems,

ho wev er ,

and

in

fac t th e

d iagrams

are

appl icab le

only

to

those f lexible wa l l

sys tems

in

w h i c h

•

verexcavat ion to

facil i tate

ground

anch or

instal lat ion

does

n ot

occur.

•

rou nd

anch or

pre loading

is

compat ib le

with act ive

l imit

state

cond i t ions .

• he water table

is be low th e base

of

th e

wall .

T he

des ign

of f lexible wal l

sys tems

is

i l lustrated

in Ebeling

et

al .

(2002) .

1 .2

esign o f

Stiff

Tieback

Wall Systems

Cons t ruct ion-sequencing

analyses are

impor tan t

in

th e

evalua t ion

of

stiff

t ieback

wal l sys tems,

since fo r such

sys tems

th e t emporary

construct ion

stages

are often

m o r e d em a n d in g

than

th e

f inal

pe rm ane n t

loading

cond i t ion

(Kerr

a n d

T a m a r o

1990) .

T hi s

m ay

also

b e

true

fo r

f lexible wa l l

sy s t em s wher e

s ign if ican t

overexcavat ion occurs

an d

fo r f lexible wa l l

sys tems

sub jec t to

a n c ho r

pres t ress

loads producing

soil

pressures

in

ex c es s

of

act ive

l imi t

state condit ions.

T he

purpose of th e

ex a m p l e p r o b l em s

conta ined here in

is to

i l lustrate

th e

use of

cons t ruct ion-sequencing analys is

fo r th e

des ign

of

stiff

t ieback wal l

sys tems.

Al t ho u g h

m a n y

types

of


analyses

ha v e

b een

used

in

th e

des ign

of

t ieback

wal l

sys tems,

only

three

types

of


analyses

are

demons t ra ted

in

th e

ex a m p l e prob lems.

T h e three

const ruc t ion-

sequencing

analyses

chosen

fo r

th e

ex a m p l e p r o b l em s

are

ones

considered

to

b e

th e m o s t

promis ing

fo r th e des ign

and

evalua t ion

of

C o r p s

t i eback wal l

sys tems:

•

quiva len t

b ea m

on

r igid suppor t s

by

c lass ica l m et ho d s

( ident if ied

as

th e

RIGID

2

m et ho d by

Strom and

Ebeling

2002) .

•

ea m

on

inelast ic

foundat ion m et ho d s using

elastoplast ic

so i l -p ressure

deformat ion

curves

(R-y

curves)

that

a c c o u n t

fo r

plast ic

(nonrecoverab le)

m o v em en t s

( identi fied

as

th e

W IN K L E R m e t h od

b y

Strom and

Ebel ing

2002) .

•

eam

on

inelast ic foundat ion m et ho d s

using elastoplast ic

soil -pressure

deformat ion

curves

(R-y

curves)

fo r th e

resist ing

side

only with

c lass ica l

soil

pressures

appl ied

on th e

dr iv ing

side

( ident if ied

as th e W IN K L E R

2

m e t h od

b y

Strom and

Ebel ing

2002) .

T h e

resul ts from

these

three


m et ho d s are

com pare d

in

Strom and

Ebel ing

(2002)

with

th e

resul ts obtained fi-om th e

equiva len t

beam

on

r igid

suppor t m et ho d using

apparent

pressure

load ing

( ident if ied here in

as

th e

R I G I D

method) . Recal l

that

apparent

earth

pressures

a re an

envelope of

m a x i -

m u m past pressures

encountered

ov e r a ll

stages

of

excavat ion .

T h e resul ts

are

also

c o m p a r ed

with f ield

m ea su r em en t s

an d finite

e l em en t

analyses

in Strom and

Ebeling

(2002) .

Chapter

1

Background

on

Tieback

Retaining

Wall

Systems


12/90

1 .2 .1

dentifying

stiff wall

systems

Five focus

w al l

sys tems

w e re

identi fied

a nd

descr ibed

in detail

in

Strom and

Ebel ing (2001):

•

ert ical

sheet-pile

sys tem with wa l es

and post-tensioned t i eback anchors .

•

oldier b e am sys tem with w o o d or reinforced

concre te

l agging a n d pos t -

tensioned tieback anchors .

For th e w o o d l agging sys tem,

a

pe rm ane n t

concre te

fac ing

sys tem is required .

• e can t

cyUnder

pile

system

with

pos t - tens ioned t i eback anchors .

• ont inuous

re inforced concre te

slurry

w al l system

with

post-tensioned

tieback anchors .

•

i screte

concre te

slurry

w al l

sys tem

(soldier

b e a m s

with

concre te

l agging)

with

pos t - tens ioned t i eback anchors .

D ef o r m a t io n s an d

wa l l

m o v em en t s in

excavat ions are a

funct ion

of

soil

strength a nd wa l l

st iffness, with

w al l

st iffness

a

function

of

structural rigidity

El

of

th e w al l

an d th e vert ical

spac ing

of

a n c ho r s L. Soil

st iffness

correlates to

soil

strength;

therefore ,

soil

strength

is

often

used in

lieu of soil

st iffness

to

charac-

terize

th e

in f luence of

th e

soil on

wa l l d isp lacements .

Steel

sheet-pile

an d

steel

so ld ier

b e a m s

with timber l agging

sys tems are cons idered

to

b e f lexible tieback

w al l sys tems. Secant

cyUnder

pile,

cont inuous

concre te

slurry wal l ,

and discrete

concre te

slurry

wa l l

sys tems are

considered

to b e stiff

t i eback w al l

sys tems.

T h e

effect

of

wall

st iffness

on

wall d isp lacements

an d

earth

pressures

is descr ibed

in

X ant h akos

(1991)

an d

in

F H W A- R D - 8 1 - 1 5 0 .

In th e F H W A report ,

it

is

ind icated

that

C l o u g h

a nd

T su i

(1974)

sho wed , by finite e lement analyses , that w al l

an d

so i l

m o v em en t s

could

b e reduced by

increas ing

wall rigidi ty

an d

tieback

stiffiiess.

None

of

th e

reduct ions

in

m o v em en t s

w e re

proport ional

to

th e

increased

stiffiiess,

ho wev er .

For

example ,

an

increase

in

wa l l rigidity

of 32

t imes

reduced

th e m o v em en t s by a factor

of

2 .

Lik ewise ,

an increase

in

th e t i eback

stiffiiess by

a

factor of 10 caused

a

5 0

percent reduct ion in

m o v em en t s .

O t h e r inves t iga tors ha v e

also

s tud ied th e ef fec t

of support

st iffness

fo r

c lays

(a s

reported

in

F H W A - R D - 7 5 - 1 2 8 ) .

T h e y def ined

sys tem

st iffness

by

EIIL'^,

w h e r e

El

is

th e

stiffiiess of

th e wa l l

and

L

is

th e

d is tance b e t w e e n

suppor t s

(F igure 1-1).

T h e m ea su r e

of

w al l

st iffness is

def ined

as a

variat ion on th e

inverse

of

Rowe's

f lexibil i ty

n u m b e r fo r wal l s ,

an d

is thus expressed by

EIIL^,

w h e r e

L is

th e vert ical

d is tance

b e t w e e n tw o

r o ws

of anchors .

Wall

st iffness

refers not only to th e

structural rigidi ty der ived f rom th e elast ic m o d u l u s

an d th e

m o m e n t

of inert ia , but also

to

th e

vert ical

spac ing of suppor t s

(i n this

case

anchors) .

It

is

suggested

by

Figure

9-106

in

F H W A -R D-7 5 -1 2 8

that ,

for

stiff

c lays with

a

stabil i ty

n u m b e r

Y///5„

equal to or less than 3,

a

sys tem

st iffness

EIIL^

of 10 o r

m o r e

w ou l d

keep

soil

displacement

equal

to

o r

less

than in.' '^

H o wev er ,

other

factors,

such

as

pres t ress level ,

overexcavat ion,

an d factors

of

'

t this t ime, th e aut hors of this repor t r e c o m m e n d that ,

when

t ieback w a l l system d isp lacement s

a re

th e

quantity

of in t e res t

(i.e., s t r ingent

d isp lacement

control

design) ,

they

should

b e

estimated by

nonlinear finite e lement -so i l st ructure interact ion ( N L F E M ) analysis .

^ table of factors

fo r

conver t ing non-S I

units

of m e a s u r e m e n t t o SI

units

is

presented

on page

vii.

Chapter

1

Background

on

Tieback

Retaining

Wall

Systems


13/90

s\vs\vs\

k^^V^V^S sV^\\\

Ground anchor (typ)

Figure

1-1.

efinition

of

span length

L

safety,

also

influence

displacement. Data

in

this

figure

clearly

indicate

that

stiff

wall systems in stiff clays will displace less than flexible wall systems in soft

clays.

Table

1 - 1 categorizes flexible and stiff

wall

systems with respect to th e

focus wall systems of th e Strom and Ebeling (2001) report.

Table

1 -1

Stimiess Categorization of

Focus Wall Systems (Strom an d

Ebel ing

2001 )

Focus

Tieback

Wall

System Descript ion

Wall Sti ffness Cateqorv

1

Flexible

stiff

Vertical

sheet-pile

system

V

Soldier beam

system

V

Secant cylinder pile

V

Continuous reinforced

concrete

sluny

wall

system

V

Discrete

concrete slurry

wall

system

V

Using th e approach ofFHWA-RD-75-128, th e wall stiffness ca n be quanti-

fied in terms of th e flexural stiffness El per

foot ru n ofwall and in terms of th e

relative flexural stiffness E I / L ' * . This

information

is

presented in

Table

1-2

fo r th e

focus wall systems of th e Strom

an d

Ebeling (2001)

report.

T he relative flexural

stiffness in th e table

is

based on a span length

L,

i.e., a vertical

anchor

spacing of

10

ft.

It should be

recognized

from these stiffness

calculations

that

a secant

pile

system

with

L equal

to

28.5 ft would produce

a

flexural stiffness value of^//Z,

equal

to

that for th e vertical sheet-pile wall system with L equal

to

10

ft. There-

fore, it

is

possible, by spacing anchors at close intervals, to obtain a stiff wall

system

using

flexible sheetpiling or , vice versa,

to

obtain

a

flexible

wall

system

using secant piles with widely spaced anchors.

Chapter

1

Background

on

Tieback

Retaining

Wall

Systems


14/90

Table

1 -2

Genera l Stif fness Quantif ication

fo r

Focus Wall

Systems

(Strom

and

Ebel inq

2001 )

Waif Sti ffness

Wall

System

El

k-ft^/ftx10*

EIIL*

ksf/fl

Flexible

Vertical

sheet-pile

system

0. 3

to

5. 0

3.7^

Soldier beam system

0.1

to 4. 0

1.5^

Stiff

Secant

cylinder

pile

8. 0 to 250.0

239.8 ̂

Continuous

reinforced

concrete slun^

wall

30.0

to

150.0 123.1

Discrete concrete

slun^

wall

35.0 to

160.0

92.3 =

Relative

stiffness

based

on

P Z

27 sheetpiling.

P er Olmsted Prototype

Wall.

^ Relative stiffness

based

on

HP12x53

soldier

beams

spaced

at 8. 0 ft

on

center

(OC).

P er

FHWA-

RD-97-130 design example.

^

Relative stiffness based

on

5.0-ft-diam caisson piles spaced at 7. 0 ft OC . P er Monongahela

River

Locl


15/90

r ec o m m en d a t io n s

of F H W A -R D-9 7 -1 3 0 .

Trapezoida l

earth

pressure

distr ibut ions

are used fo r this

type

of

analysis.

For stiff wal l sys tems,

act ive

earth pressures

in

th e

retained soil

can

often b e

a s su m ed an d u sed

in

a


analys i s

to size

anchors

and

determine

wal l

proper t ies .

Earth

pressure

distr ibut ion

fo r

this

type

of

analysis

w ou l d

be

in

accordance with

c lass ica l

earth

pressures

theory ,

i.e.,

t riangular

with

th e absence

of

a

water

table .

T h e

genera l prac t ice

fo r

th e

safety

with

e c o n o m y des ign

is to

k eep

anchor

pres t ress

loads

to

a

m in im u m consis ten t with act ive,

o r near-ac t ive ,

soil

pressure

cond i t ions

(depend ing

u p o n

th e value

ass igned

to th e

factor of safety).

T hi s

m ea n s

th e

anchor size

wo u l d

be

smaller ,

th e anch or

spac ing

larger,

and

th e

anch or

pres t ress

l o wer than those

found

in des igns

requir ing stringent

displacement control .

1.2.2.2 Stringent displacement control design.

A

pe r fo rm ance objec t ive

for

a

t i eback

wal l can b e

to

restrict

wal l and soil

m o v em en t s

dur ing

excavat ion

to

a

tolerable

level so

tha t structures

ad jacent

to

th e excavat ion

wil l

n ot exper ience

distress (a s

fo r

th e Bonnevi l l e

t emporary

t ieback

wal l

example) .

Ac c o r d in g

to

F H W A -R D-8 1 -1 5 0 ,

th e

tolerable

ground

surface

se t t l ement m ay b e

less than

0.5 in .

if

a se t t l ement -sens i t ive

structure

is

founded on

th e

sa m e

soil

u sed

fo r

suppor t ing th e

anchors .

T i e b ack

wal l

des igns

tha t are

required

to

m e e t

spec i f ied

displacement control performance

objec t ives

are

t e rmed

s t r ingent

displacement

cont ro l des igns .

Select ion

of th e

appropr ia te

des ign pressure

d iagram

fo r

deter-

mining anchor prestress

load ing

d ep en d s on th e

level

of

wal l

an d

soil

m o v e m e n t

tha t can b e tolerated. Walls buil t

with

factors

of safety

b e t ween

1.3 and 1.5

appl ied

to

th e

shea r

strength

of

th e soil

m ay

result

in

smal ler

d isp lacements

if

stiff wal l

c o m p o n en t s

are

used

( F H W A- R D - 9 8 - 0 6 5 ) .

T o m in im ize th e o u t wa r d m o v em en t ,

th e des ign wo u l d proce e d using

soil

pressures

at

a

magni tude

approach ing

at-rest

pressure cond i t ions (i.e., a

factor

of

safety

of 1.5

appl ied

to th e shear

strength

of

th e

soil).

It should b e recognized tha t

even

though th e

use

of a

factor of

safety

equal to 1.5 is

consis ten t with

an

at-rest

(i.e.,

zero

so i l -d isp lacement cond i t ion) earth

pressure

coeff i c ient

(as

s h o w n

in

Figure

3 -6 of

Engineer

M a n u a l

1110-2-2502

(Headquar ters ,

U . S .

A r m y

C o r p s

of

Engineers

1989)) ,

severa l

types

of

lateral wa l l

m o v e m e n t could

still occur.

T h e s e

inc lude cant i lever m o v em en t s

assoc ia ted with

instal lat ion

of th e fi rs t

anchor ;

elast ic

elongat ion

of th e

t endon

a n c ho r

assoc ia ted

with

a

load

increase;

anchor

yie ld ing,

creep ,

and

load

redist r ibut ion

in th e anchor b o n d zone;

and m a s s

m o v e-

ments

behind

th e

ground

a n c ho r s

( F H W A- S A- 9 9 - 0 1 5 ) .

It

also

should

be

recog-

nized

that

a

stiff rather than

f lexible wal l

sys tem

m ay b e required

to

reduce

bending

d isp lacements

in th e wal l to levels cons i s tent with th e pe r fo rm ance

objectives

es tab l ished fo r th e

s t r ingent

displacement

control

design.

A s t r ingent

displacement

cont ro l

des ign

fo r

a

f lexible wal l

sys tem,

ho wev er ,

w ou l d

result

in

anch or spac ings

that

are

closer an d anch or pres t ress

levels

that are higher than

those

fo r

a

comparab le

safety with

ec o n o m y des ign .

If

displacement

cont ro l

is a

crit ical pe r fo rm ance

objec t ive

fo r

th e

project be ing des igned ,

th e use

of

a

stiff

rather than f lexible wa l l

system should be considered .

Chapter

1

Background

on

Tieback

Retaining

Wall

Systems


16/90

1 .2 .3

rogressive

design of tieback

wall

systems

A s with m o s t des igns ,

a

progress ive analys i s

(start ing

with

th e

s imples t

des ign

tools and progress ing to

m o r e

c o m p r ehen s iv e

des ign

tools w h e n neces -

sary) is high ly r e com m e nd e d

by

th e

authors.

With

respec t

to

f lexible

wall

sys tems,

so m e of th e

m o r e

c o m p r ehen s iv e

analys i s

tools

used

for

stiff w al l

sys tem analysis

(cons t ruct ion-sequencing analys i s

b a sed

on

c lass ica l

earth

pressure

distr ibut ions

an d

b e am

on

inelast ic

foundat ion

analys is ) are not

g en -

eral ly

cons idered

appropr ia te

for th e

analys is

of

f lexible

w al l sys tems .

T hi s

is

because apparent pressure

d iagrams, since they

are

envelopes based on m e a -

surements m a d e

during const ruc t ion ,

inc lude th e

effects of soil

arching ,

wall

f lexibil i ty ,

pre loading

of

suppor t s ,

facial st iffness,

an d

construction

sequencing .

H o wev er ,

with stiff wa l l

sys tems,

these

i t ems wil l no t

af fec t

earth pressure

redis tribution

to

th e

sa m e

exten t

they

af fec t

f lexible wa l l

sys tems.

Therefore ,

in

pract i ce , cons t ruct ion-sequencing

analyses

and

b ea m

on

inelast ic

foundat ion

analyses

are considered valid tools

for th e invest igat ion of

stiff

wa l l

system

behav ior .

T he

des ign

a nd

analysis tools typically used in th e

des ign an d analysis

of

f lexible a n d

stiff

wa l l sys tems a re

su m m a r ized

in

Tables

1-3

a nd

1-4,

respec-

t ively,

start ing

with

th e

s imples t

des ign

tool

and

progress ing to th e m o r e c o m p r e -

hens ive analy t ica l tools.

T h e m o s t c o m p r ehen s iv e des ign tools

are

l inear elast ic

finite

e l em en t

( LE F E M )

and nonl inear finite

e l em en t

( N L F E M )

soil -st ructure

interact ion

analyses .

T h e

N L F E M

analysis

is

required

w h e n it

b e c o m e s

necessary

to verify that

th e

des ign meets

s t r ingent

displacement

cont ro l

pe r fo rm ance

object ives.

Both

th e

LEFEM

a n d

NLFEM

analyses

can be

used

to verify

safety

with

ec o n o m y

des igns .

Table 1 -3

Des ign

and

Analys is Tools

for

F lex ib le

Wall Systems

(Ebel ing

e t

al.

2002)

nalysi

s

Objective

Descript ion

Analysis iVIethod

RIGID

1

Final

design

when

performance goal is

safety with

economy.

P reliminary design

when

performance

goal

is stringent

displacement

control.

Beam

on rigid supports analysis

using

apparent

pressure "envelope" diagram.

Apparent pressure diagram based on a

total

load

approach.

Total

load

is

based

on

a

factor

of

safety

of

1. 3 applied to the

shear

strength of

the

soil

when

the

performance goal

is

safety

with

economy

Total

load

is based on a factor of safety

of 1. 5 applied to the shear strength of

the soil

when

the performance goal

is

stringent

displacement

control.

Hand

calculations

NLFEM

Final design when

performance goal is

stringent displace-

ment

control.

Nonlinear soli-structure

finite

element

construction-sequencing

analysis.

P C

SOILSTRUCT-

ALPHA

Chapter

1

Background on

Tieback



17/90

Table 1 -4

Des ign

and Analysis

Tools

for

Stiff

Wall

Systems

(Strom

an d

Ebel ing

2002)

Analysis

RIGID

1

RIGID

2

Objective

Preliminary design tool to

estimate upper anchor

loads an d bending

moments

in

upper

region

of

wall.

Construction-sequencing

analysis

using

classical

soil pressures.

Used to estimate lower

anchor loads

an d

bending

moments in lower regions

of wall.

WINKLER

1

WINKLER

2

LEFEM

NLFEM

Description

Beam

on

rigid supports analysis using apparent

pressure

"envelope" diagram.

Apparent

pressure

diagram

based

on

a

total

load

approach.

Total

load is

based

on

a

factor

of

safety

of

1. 3

applied to the

shear strength

of

the soil

when

the performance

goal

is

safety

with economy

Total

load

is

based

on

a

factor

of

safety of

1. 5

applied to the

shear

strength

of

the

soil

when

the performance

goal

is

stringent displacement control.

Beam

on

rigid

supports analysis.


analysis to affirm results

of RIGID

1

an d

RIGID 2

analyses.



of

RIGID

land

RIGID

2

analyses.



of

RIGID

land

RIGID

2

analyses

an d

to evaluate

3- D effects and

investigate loss of

anchor

effects.

Used

for cases where

bending effects in the

longitudinal direction are

important.

Final

design

when

performance goal

is

stringent

displacement

control.

Soil-pressure distribution by classical methods, i.e.,

Rankine,

Coulomb, etc.

Active pressures used to determine anchor loads

an d

wall

bending moments based on a factor of safety of 1. 0 applied

to

the

shear

strength

of

the

soil

when

the

perfomiance

goal

is

safety

with

economy.

At-rest

earth

pressures used to detennine anchor loads an d

wall bending moments based on

a

factor of

safety of

1. 5

applied to the

shear

strength

of

the soil when

the

performance

goal

is

stringent

displacement

control.

Passive

pressures used

to determine

anchor loads

and wall

bending

moments based

on

a factor

of

safety

of

1. 0 applied

to the

shear

strength of

the soil.

Beam

on

inelastic supports

analysis.

inelastic springs used to represent

soil

on both sides of

wall.

Inelastic springs

used

to represent anchors.

R-y

curves

shifted

to

account

for

inelastic

soil

deformations.

Beam

on

inelastic

supports analysis

inelastic springs used to represent soil

on

excavated

side

of

wall.

Classical soil pressures applied to retained

earth

side

of

wall.

inelastic springs used to represent anchors.

Plate

elements

used to represent

wall

to

capture

redistribution

effects

in the longitudinal direction of

the

wall.

Elastic

springs used to represent soil

on

excavated

side

of

wall.

Classical

soil

pressures

applied

to

retained

earth

side

of

wall.

Elastic

springs used to represent

anchors.

Nonlinear

soil-structure

finite

element construction-

sequencing analysis

Analysis Method

Hand

calculations

Hand

calculations

for determinate

systems.

CBEAMC equivalent

beam

analysis

for

indeterminate

systems.

CMULTIANC

beam

I

on inelastic supports

analysis.

CBEAMC beam

on

nonlinear supports

analysis.

Structural analysis

software with plate

element analysis

capability.

P C SOILSTRUCT-

ALPHA.

Chapter

1

Background

on

Tieback

Retaining

Wall

Systems


18/90

Descr ip t ions

of

th e

analys i s

m et ho d s

cited

in

Tables

1-3

a nd

1- 4

an d

used

in

th e ex a m p l e p r o b l em s

are provided in

Strom and Ebel ing

(2002) .

With respect t o

th e

W IN K L E R

b e am on inelast ic spring

analyses

cited

in these

tables,

there

are

severa l m et ho d s

fo r cons t ruct ing

th e spring

load-d i splacement

(R-y)

curves.

T hese m et ho d s

are

su m m a r ized in T a b l e 1-5

an d descr ibed in th e first ex a m p l e in

Strom

an d

Ebel ing (2002) .

Table

1 -5

Summary

o f

R-y

Curve

Construction

Methods

(Strom

an d

Ebel ing

2001 )

Method

Constant of

Horizontal Subgrade

Reaction/ Subgrade

Constant

Soletanche

Reference Deflection

Method

Descript ion

A constant of horizontal subgrade reaction method was developed by

Terzaghi

(1955) for use in the evaluation of

discrete wall systems. A

subgrade

constant

method

was

also

developed

for

continuous walls.

Interaction distances used

In

the

analysis

are

pe r

Haliburton (1981).

IVIethods

generally

provide

a

reasonable estimate

of wall moments

an d

shears, bu t

often

overestimate displacements.

FHWA-RD-81-150 presents coefficients

of

subgrade reaction based on

information obtained

from

pressure meter

tests.

Subgrade reaction values

are

a function of the shear parameters of the soil. Soletanche used beam

on inelastic foundation analyses, based on the P fister co efficient of

subgrade reaction values, to

verify

that

anchor

loads an d computed wall

displacements

me t performance objectives.

Method

reported

in

FHWA-RD-98-066 for use

in

beam

on

inelastic

foundation analyses. Displacements representing the

elastoplastic

intersection point of

the R- y curve were established for granular

an d

clay

soils.

R- y curves are shifted to account for inelastic

nonrecoverable

displacements. These investigators indicated that

th e

deflection response

estimated

by the

reference deflection method

generally underpredicted

displacements because

it

does no t account for mass movements in the

soil.

1 .3

IGID

1 Method

In

th e

R I G I D

m e t h od

(Strom and

Ebeling

2002) ,

a

vert ical

strip

of

th e

t i eback

w al l

is

t reated

as a

mult i span b e am suppor ted on rigid

suppor t s

located

at

tieback points

in th e upper region

of

th e wal l .

T h e l ow e rm os t rigid support is

as s u m e d

to

occu r a t

f inish

grade.

T h e

wa l l

is loaded on

th e

driving side

with an

apparent pressure

load ing .

In

genera l

prac t ice ,

th e

u se

of soil pressure

envelopes

as

load ings

fo r

a

b e am

on

rigid

support

analys is

provides

an

expedient

m e t h od

for th e init ial layout ,

an d so m et im es th e f inal des ign

of

t i eback

w al l

sys tems.

H o wev er ,

th e

soil pressure

envelopes ,

o r apparent

earth

pressure d iagrams, wer e

not

in tended

to

represent

th e

real

distribution

of

earth

pressure , but ins tead

consti tuted hypothe t i cal pressures .

T hese hypothe t i cal pressures w e re a bas i s

fi-om w h i ch strut loads

could b e

calculated that m i g h t b e

approach e d but wo u l d

no t

b e

ex c eed ed

dur ing

th e

ent ire const ruc t ion process .

T h e

apparent pressure loading used in th e ex a m p l e

p r o b l em s

is

in accordance

with

F H W A- R D - 9 7 - 1 3 0 .

(See

Figure

2 8

of

this

F H W A report fo r

th e

apparent

pressure

d iagram used

fo r

a wall suppor ted by

a

single row

of

a n c ho r s

an d Fig-

ure

29

fo r th e

apparent pressure

d iagram

used fo r a w al l supported by mult iple

r o w s

of

anchors . ) T hi s

informat ion

is

also

presented

in Strom

an d

Ebeling (2001,

Figures 5 .3

and

5.4) .

Chapter 1 Background on

Tieback



19/90

R I G I D

des ign

procedures

are

i l lustrated

in th e

ex a m p l e prob lems

conta ined

in

Strom and Ebel ing

(2002)

and

in

th e

ex a m p l e

prob l e m s in

Sect ion

10 of

F H W A- R D - 9 7 - 1 3 0 .

W hen t iebacks

a rc pres t rcssed

to levels

consis ten t

with

act ive pressure

cond i t ions

(i.e.,

E x a m p l e

in

Strom and

Ebeling

2002) ,

th e

tota l

load

used to determine

th e

apparen t

earth

pressure

is

based

on

that

approximate ly

corresponding

to

a

factor

of

safety

of 1.3

on

th e

shear

strength

of

th e

soil.

W hen

t iebacks

are prestrcssed to

m in im ize

wal l displacement

(Example 2

in

Strom

an d

Ebeling

2002) ,

th e

total

load

u sed

to

determine

th e

apparen t

earth

pressure

is

b a sed on

at-rest earth

pressure

coef f ic ien t cond i t ions ,

or that

approximate ly

corresponding

to

a

factor of

safety

of 1.5 appl ied

to

th e shear

strength

of

th e soil.

Empir ica l

formulas

are

provided

with th e

appare n t

pressure

m e t h od

fo r

u se

in

est imating

anch or

forces

and wal l

bend ing m o m en t s .

1 .4

IGID

2

Method

A s

with

th e

RIGID

m et ho d ,

a

vert ical

strip of th e

t ieback

wa l l

is

t reated

as

a

mul t ispan

b ea m suppor ted on

r igid supports

located at

t i eback

poin t s

(Strom

and

Ebel ing

2002) .

T he

l o wes t

suppor t locat ion

is

a s su m ed to

b e

below

th e

bot tom of

th e

excavat ion

a t th e

poin t

of

zero net pressure (Ratay 1996) .

T w o

earth

pressure

d iagrams

are

used

in

each

of th e

incrementa l

excavat ion ,

anch or

placement ,

and prestressing analyses .

Act ive earth pressure

(o r

at-rest

earth

pressure

w h e n

wal l

d isp lacements

are

crit ical)

is

appl ied

to

th e

dr iv ing

side

and

extends

from th e

to p of

th e ground

to

th e

actual

bot tom

of

th e

wal l . Pass ive

earth

pressure

(based

on a

factor

of

safety of 1.0 appl ied to th e

shear strength

of

soil)

is

appl ied

to th e

resist ing

side

of

th e wal l

a n d

extends

from th e bot tom

of

th e

excavat ion

to th e actual

bottom

of

th e wal l .

T he

appl ica t ion

of

th e

R I G I D

2

m e t h od is

demonst ra ted

in

th e

tw o ex a m p l e

prob l e m s in Strom

an d

Ebeling

(2002) .

T he

RIGID

2

m et ho d

is

useful

fo r

de te rmining if th e

wal l

a n d anch or

capac i t ies determined

b y

th e

RIGID

analys is are adequate

fo r

stiff

t ieback

wa l l

sys tems,

an d

permit s redes ign

of

both

f lexible an d

stiff

t ieback wa l l

sys tems

to

ensure tha t strength

is

adequate

fo r

all

stages

of

const ruc t ion . N o useful

in forma-

t ion

can b e

ob ta ined

from th e R I G I D 2

analys is

regard ing displacement d em a n d s ,

ho wev er .

1 .5

WINKLER1

Method

T h e W IN K L E R m e t h od (descr ibed

in

Strom

and Ebel ing

2 0 0 2 ) uses

ideal ized

elastoplast ic

springs to represent soil

load-deformat ion

response

an d

anchor

springs

to

represent

grou nd

anch or

load-deformat ion

response .

T he

elastoplast ic

curves

(R-y curves)

represen t ing th e

soil

springs

for th e ex a m p l e

prob l e m s are

b a sed

on th e

reference

deflect ion

m e t h od

( F H W A- R D - 9 8 - 0 6 6 ) .

Other m et ho d s

are avai l ab le

for develop ing

elastoplast ic

R -y

curves

for b ea m

on

inelast ic

foundat ion

analyses.

T he

reference

deflect ion

m e t h od

( F H W A - R D - 9 8 -

0 6 6 ) ,

th e Haliburton

(1981) m et ho d ,

an d th e Pfister m et ho d

( F H W A- R D - 8 1 - 1 5 0 )

a re

descr ibed

in

th e f irst

ex a m p l e

prob lem.

Elastoplast ic curves can be shif ted

with

respec t

to

th e

undef lected

posit ion

of

th e

t i eback

wa l l to capture

non-

recoverab le

plast ic

m o v em en t s that m ay occu r in th e

soil

dur ing

var ious

con-

struct ion s tages

(e.g.,

excavat ing ,

anch or

placement ,

and prestressing

of

anchors) .

'

^

hapter

1

Background

on

Tieback

Retaining

Wall

Systems


20/90

T hi s R -y

curve

shif t ing

w as used in both

ex a m p l e

prob l e m s

to

cons ider th e

n o n -

recoverab le

act ive

state

yielding

that occurs

in

th e retained soil

during th e first-

stage excavat ion (canti lever-s tage excavat ion) .

T h e R -y curve

shif t

fo l lowing

th e

f irst -stage

excavat ion wil l help to

capture th e

increase

in

earth

pressure

that

occurs behind th e

w al l

as

a n c ho r pres t ress

is

appl ied ,

an d

as

second-s tage ex c a v a -

t ion

t akes

place.

In th e tw o

ex a m p l e

p r o b l em s

in

Strom an d Ebeling (2002) ,

once

th e upper anchor

is

instal led,

th e

second-s tage

excavat ion causes th e

upper

sec t ion

of

th e t i eback wall to

def lec t

into th e retained

so i l—soi l

that h as previ -

ously

exper ienced

act ive

state

yie ld ing

dur ing f irst -stage

excavat ion .

T h e

WINKLER

m e t h od

is

useful

fo r

determin ing if th e wall and a n c ho r capac i t ies

de te rmined by a R I G I D or RIGID 2

analysis

are adequate ,

an d permit s redes ign

of

stiff

t i eback w al l

sys tems

to

ensure that strength

is adequate

fo r a ll

stages

of

computer program for simulation of wall construction sequence

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