Report No. CDOT-DTD-97-10

LOADING TEST OF GRS BRIDGE PIER AND ABUTMENT IN DENVER, COLORADO

Kanop Ketchart Jonathan T.H. Wu Reinforced Soil Research Center Department of Engineering University of Colorado at Denver

Final Report October 1997

Prepared in cooperation with the U.S. Department of Transportation Federal Highway Administration

The contents of this report reflect the views of

the author who is responsible for the· facts and

the accuracy of the data presented herein. The

contents do not necessarily reflect the official

views of the COlorado Department of Transportation

or the Federal Highway Administration. This report

does not constitute a standard, specification, or

regulation.

i

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1. AGENCY USE ONLY (WveBlank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

October 1997 Final Report

4. 1TILE AND SVB1'JTI.E 5. ruNDlNG NUMBERS

T .noci T".t of GRS ~ : Pier onci in ~

6. AUl'HORS(S)

K ''1on .nn ,'LU W11

7. PERFORMING ORGANIZATION NAME(S) AND AIlDR&SS(S) 8. PERFORMISG ORGANlZAl1ON

Reinforced Soil Research Center REPORT NUMBER

Department of Civil Engineering

University of Colorado at Denver

9. SPONSORINGiMONlTORING AGENCY NAME(S) AND ADDRESS(S) 10. SPONSORING/MONITORING

Colorado Department of Transportation AGENCY REPORT NUMBER

4201 E. Arkansas Ave.

Denver, Colorado 80222 CDOT -DTD-97 -10

11. SUPPLEMENTARY NOTES

Prepared in Cooperation with the U. S. Department of Transportation, Federal

Highway Administration

120. DISI1UBUfION/AYAILABn.rrv STATEMENT 12b. DISTRIBU'IIOS CODE

No Restrictions: This report is available to the public through the "T _ . ,1 ~. " . ,,- -'" _. VA n161

13. ABSTRACf (Maximum 200 words)

A GRS bridge abutment and two GRS bridge piers were constructed inside a 3.5-m deep pit in Denver, Colorado. The structures

were constructed with a "road base n backfill and reinforced with layers of a woven geotextile. Dry-stacked hollow-cored concrete

blocks were used as facing. One of the piers and the abutment, both 7. 6 m in height, were load tested The load was applied using

concrete barriers stacked in seven layers over three steel bridge girders. A total load of2, 340 IcN, corresponding to 232 kPa

vertical pressure, was applied. The pier and the abutment were instrumented with metal pipes and elastic springs to monitor the

vertical and lateral movement of the facing, and strain gages to monitor deformation of the reinforcement. This report describes

the configuration of the structures, the material properties of the backfill and the geotextile reinforcement, the construction

procedure. the loading schemes, and the instrumentation. The report also presents measured results and discussions of the

measured results.

14. SUBJECT TERMS 15. NUMBER OF PAGES

Fortress, Reinforcement, 62

Geosy1llh.tic,. 16. PRICE CODE

Soils,

17. SECURTITY CL4SS1FIC(T10N lB. SECURlTY CLASSIFICATION 19. SECURITY cu.ssIFiCATION 20. UMlTATION OF .UlSTRACT

OF REPORT OF THlS PAGE OF ABSTRACT

T1- J TI, -, .. n. ,.;fio/l

Technical Report Documentation Page

Table of Contents

Chapter

1. Introduction .................................................................................... .

2. P · D .. roJect escnptlOn ......................................................................... .

3. Materials ........................................................................................ . 3.1 Backfill.. ............................................................................ .. 3.2 Geotextile Reinforcement. ................................................. ..

4. Construction .................................................................................. .

5. Loading Scheme ........................................................................... ..

6. Instrumentation .............................................................................. . 6.1 Vertical Movement. ........................................................... .. 6.2 Lateral Movement.. ........................................................... .. 6.3 Strains in Reinforcement.. ................................................... .

7. Results of the First-Stage Load Test.. ............................................ .. 7.1 Short-Term Behavior ......................................................... ..

7.1.1 Vertical and Lateral Displacements .......................... . 7.1.2 Strains in Reinforcement.. ...................................... ..

7.2 Long-Term Behavior under 1,170 kN Load ........................ . 7.2.1 Vertical and Lateral Creep Displacements .............. .. 7.2.2 Creep Strains in Reinforcement... ............................ .

8. Summary and Conclusions .............................................................. .

I

3

7 7 7

10

25

28 28 28 32

36 36 36 44 46 46 53

58

References..... ... ... ......... ... ... ... ... .... ... ... .... ..... ..... ... ... ....... ... ........ ... .......... ..... 61

Acknowledgements.......... ... ... ... .... ... ... ......... ..... ...... .... ........ ................ ........ 62

ii

List of Figures

Figure No.

1 Side View of the Structures

2 Top View of the Structures

3 Gradation Curve

4 First-Stage Load Test

5 Instrumentation for Vertical and Lateral Movements

6 Locations of the Leveling Rods

7 Locations of the Reinforcements with Strain Gages and the

Elastic Springs

8 Strain Gage Attachment

9 Strain Gage Calibration in the Fill Direction of the Reinforcement

10 Strain Gage Calibration in the Warp Direction of the Reinforcement

11 Vertical Displacement versus Applied Load Relationships of the

Abutment

12 Lateral Displacement versus Applied Load Relationships of the Abutment

13 Vertical Displacement versus Applied Load Relationships of the Outer

Pier

14 Lateral Displacement versus Applied Load Relationships of the Outer Pier

15 Vertical and Lateral Movements of the Outer Pier and the Abutment at

1,170 kN

16 Reinforcement Strain Distributions in the Abutment

17 Vertical Creep Displacement versus Time Relationships of the Abutment

18 Lateral Creep Displacement versus Time Relationships of the Abutment

19 Vertical Creep Displacement versus Time Relationships of the Outer Pier

20 Lateral Creep Displacement versus Time Relationships of the Outer Pier

21 Average Vertical Creep Rate at Top of the Outer Pier and the Abutment

iii

22 Reinforcement Creep Strain Distributions in the Abutment

23 Reinforcement Creep Strain Distributions in the Outer Pier

24 Average Reinforcement Creep Strain versus Time Relationships of the

Outer Pier

24 Calculated versus Measured Lateral Creep Displacements of the Outer

Pier

iv

TableNo.

I

2

List of Tables

Some Index Properties of the Reinforcement

Maximum Vertical and Lateral Movements of the Outer Pier and the

Abutment at 1,170 kN

v

Chapter 1 INTRODUCTION

Geosynthetic reinforced soil (GRS) technology has been widely used in the

construction of retaining walls, embankments, slopes, and shallow foundations. In July

1996, a 5.5-m high prototype GRS bridge pier was constructed at Tumer-Fairbank

Highway Research Center, Federal Highway Administration. A series ofloading tests have

demonstrated that the GRS bridge pier has a very high load capacity and excellent

performance characteristics under typical design loads (Adams, 1997). This study was

undertaken as a continuation of the Tumer-Fairbank's test.

The objectives of this study were three folds. The first objective was to investigate

the performance of a GRS bridge support system, including an abutment and a pier, subject

to design loads. The second objective was to investigate the long-term performance of such

a bridge support system under a sustained design load. The third objective was to examine

the performance of GRS bridge abutment and pier when constructed in a less stringent

condition.

This project was a joint effort of the Colorado Department of Transportation,

Reinforced Soil Research Center of the University of Colorado at Denver, and Tumer­

Fairbank Highway Research Center of the Federal Highway Administration. The project

1

site IS near the intersection of Interstate Highway-70 and Havana street m Denver,

Colorado.

,

Chapter 2 PROJECT DESCRIPTION

This project consisted of two piers and one abutment. These structures were

situated in a 3.53-m deep pit as depicted in Figure 1. The outer pier and the abutment were

7.6 m tall. The center pier was 7.3 m tall, 0.3 m shorter than the outer pier and the

abutment. The pier was made shorter for the purpose of a second-stage load test to be

conducted at a later time.

The center pier and the abutment were of a rectangular shape and the outer pier was

of an oval shape, as shown in Figure 2. The bases of the outer pier, the center pier, and the

abutment were 2.4 m by 5.2 m (major and minor axes), 2.7 m by 5.4 m, and 4.6 m by 7.2

m, respectively. The tops of the outer pier, the center pier, and the abutment were,

respectively, 1.8 m by 4.6 m (major and minor axes), 2.1 m by 4.8 m, and 3.6 m by 5.2 m.

The edge to edge distance between the outer pier and the center pier and between the

center pier and the abutment was 2.7 m.

At the bottom of the pit was a geosynthetic-reinforced soil foundation. The

reinforced soil foundation comprised three layers of geotextile reinforcement with a

constant vertical spacing of 0.3 m. The geotextile reinforcement was the same type as those

used in the piers and the abutment.

3

E

cu C)

CD c

5i:: u 5i:: d C.

E +' E , ('U ~

\0 ~

...... .1' (Y)

~ " ~ c -

Ck:

OUTER PIER

GIRDERS

- 1°.74 M

-- 2.44 M-

E E 3i:: cu cu <> <>

OJ CD c c

4i:: u 4i:: 3i:: u d d c. fil-E

+' +' ~ ('U ~ ~

\0 ~

" u u L L

~ ~ c c n; no [l! [l!

ReinforceMent Spo.cinq 0.3 I"'l

CENTER PIER ABUTMENT

Fig. 1 Side View of the Structures

(/) £. tL b::! ...... I:::: \0 (/) If)

E

13i:: (Y) If)

(Y)

• t

£.

0'> a

.,.

I---- 2.45 I'l II" 1 • 2.74 I'l "'1';' 2.74 I'l + 2.74 I'l "'1" 4.57 1'1 _I -I

I

l-f- 2.10 1'1-top

'tl d bo.se 0..

(II +' concrete

E E (II E to top r-. If') u 00 II') C> <: -..j M 0 ui bOose u

I

E E

OJ cu r-. .... - ..j tt5

E po.d E

OJ \0 - \0 ui M

E top

-t) -bOose " III

(II

I-- 2.44 1'1---j ~1Il

1.82 I'l --iI I-" '-- 0.2 M

VfE S

Outer Pier Cente r Pier AbutMent

'" Fig. 2 Top View of the Structures

The piers and the abutment were constructed on a 0.15-m thick concrete pad placed

over the reinforced soil foundation (see Figure 1). The vertical spacing of the geotextile

reinforcement in all three structures was 0.2 m. The reinforcement covered the entire top

surface area of backfill and facing blocks at each construction lift. The top four layers of

the reinforcement in the abutment employed a wrapped-around procedure behind the facing

block. A geotextile "tail", 1.2 m in length, was placed between each of these four layers to

connect the backfill to the facing blocks. Modular blocks, 0.2 m in height, were used as the

facing element for all three structures. Compaction of the backfill was conducted at each

course of the facing blocks. The facing element was made to incline from the base to the

top of approximately 5% in outer pier, 4% in the center pier and 3% in the abutment. On

the east side of the abutment, the facing assumed a 13% negative batter up to a height of

3.5 m. From 3.5 m to the top of the abutment were walking steps as shown in Figure 1.

The negative batter was made to examine the feasibility and stability of such a facing

configuration.

On top of the piers and the abutment were 0.3 m-thick concrete pads to support steel

bridge girders. The concrete pads were 0.9 m wide and 3.1 m long for the piers and 2.4 m

wide and 3.7 m long for the abutment, as shown in Figure 2. It is to be noted that the

clearance of the concrete pad was only about 0.02 m behind the back face of the abutment

facing blocks (see Figure 1).

6

Chapter 3 MATERIALS

3.1 Backfill

The backfill was a "road base" material classified as A-I-A(O) according to

AASIITO. It has 13% of fine particles (passing sieve #200). The gradation curve is shown

in figure 3. The maximum dry unit weight, per AASHTO T180 method D, is 21.2 kN/m3•

The optimum moisture is 6.7 %.

3.2 Geotextile Reinforcement

The reinforcement was a woven prolyproplylene geotextile. The geotextile

reinforcement was the same type used in the Turner-fairbank's load test.. The wide width

tensile strength in both fill and warp directions of the geotextile is 70 kN/m. The tensile

strengths at 5% strain of the fill and the warp directions are 38 kN/m and 21 kN/m,

respectively. Some index properties of the geotextile reinforcement are shown in Table 1.

7

o o - o

<D

\ \ \

\ \

o ....

_\ _\

\ \ \ \ \

\ \

o N

\ •

8

--E

~ E -CI) 8 .!:! rJ) ~ CI)

c::; 0 :e .., IU oil 0.. i:ii;

~

0

~

o 0 0

Polymer Strudure Wide Width Ten8ile Strength i Grab Tensile Strength

Type ASTM D 4595 (kN/m) ASTM D4632-86 (kN)

Stren2th (ii) 5% Strain IDtimate Stren2th (0/. (ii) Break) 1/% (ii) Break)

F'ill Direction Warp Direction fiR DIrection Warp Direction Fill Direction Warp Direction

Polypropylene Woven 38 21 70 (18"10) 70 (18%) 2.6 (20%) 2.2 (20%) I

Table 1 Some Index Properties of the Reinforcement

'"

Chapter 4 CONSTRUCTION

The construction procedure of the GRS pier and abutment is described in the

following steps:

1. Excavate a 3.5-m deep test pit;

2. Prepare the geosynthetic-reinforced soil foundation;

3. Pour and level a 0.15-m thick concrete pad on top of the geosynthetic-reinforced soil

foundation;

4. Lay a course of facing blocks conforming to the designed shape of the structure;

5. Backfill and compact in 0.2 m lifts;

6. Place a layer of geotextile reinforcement covering the entire top surface area of the

compacted fill and the facing blocks;

7. Repeat steps 4, 5 and 6 until completion.

Selected photos taken during construction of the abutment and piers are shown in

Plates I to 13.

Field density tests were performed on the center pier and the abutment during

construction. The average dry unit weight of the center pier was 19.3 kN/m3 (91% of the

modified Procter relative compaction) with the average moisture of 2.5%. For the

abutment, the average dry unit weight was 19.1 kN/m3 (90% of the modified Procter

10

relative compaction) and the average moisture was 1.6%. The density of the outer pier was

believed to be lower than these measured values as a lighter compaction plant was

employed.

11

12

. -

Plate 1 Excavation of the Construction Pit

13

Plate 2 Construction of the Reinforced Soil Foutidation

14

Plate 3 Reinforced· Soil Foundation with a Woven GeoteXtile Reinf()rcement

15

Plate 4 Laying thl' FirSt CourSe Facing Block on a ConCl'I'tl' Pad ·. . (Note the/ighi-weight compaction plant at (Jle lower left-hand corner)

16

-- ~

----

I

Plate 5 . Compaction of the Center Pier

Plate 6 · Placement ofa Layer of Geotextile R.einfor~~ment

18

Plate7 Alignment ofFacin~ Bl,ocks

.19

Plate 8 C,onstruction of the ORS Abutment with!lNegative ,Batter '

20

Plate 9 Cutting Concrete Blocks to Conform to the Designed Configuration

21

Plate 10 Placement of a Steel Bridge Girder

22

Plate 11 Three Steel Bridge Girders were Welded Together

23

Plate 12 A Clamp ofa Forklift was Used to Lifl it::r~ Barrier

24

Plate 13 Placement of Jersey Barriers

Chapter 5 LOADING SCHEME

There are two stages in the load test. The first stage was conducted on the outer

pier and the abutment. The second stage will be conducted on the center pier.

5.1 The First-Stage Load Test

Three steel bridge girders were placed over the top concrete pads of the outer pier

and the abutment. Each girder was supported by steel bearing plates resting on the concrete

pads. The steel bearing plates were located along the center line of the top concrete pad of

the outer pier, and a 0.3 m offset from the back face of the abutment facing blocks. The

span of the girders was 10.4 m. A total of 124 concrete blocks ("Jersey Barriers") was

placed on the girders in seven layers as shown in Figure 4. The total load was 2,340 kN

which corresponded to an applied pressure of 232 kPa on the outer pier. Note that such a

pressure is slightly higher than the 200 kPa maximum pressure suggested in the FHWA

Demo 82 (1996) for mechanically stabilized bridge abutments. Also note that the

maximum applied pressure of the Turner-Fairbank's test was 900 kPa which was about four

times higher than the suggested maximum pressure.

25

26

Fig. 4 . First~Stage Load Test . . .

27

5.2 The SecORd-Stal~ Load Tell

The loading scheme has yet to be detennined.

Chapter 6 INSTRUMENTATION

The focus of this project was on the second-stage load test on the center pier.

Simple devices were used in the first-stage load test to obtain some quantitative measure of

the lateral and vertical movements of the outer pier and the abutment.

6.1 Vertical Movement

A leveling rod was attached to a metal pipe, as shown in Figure 5, with one end

fixed to either the top or the base concrete pads. The vertical movement of the concrete

pads was measured by a precision survey transition of the leveling rod. Two fixed posts for

survey transit were installed outside the test pit to the north and south of the outer pier and

the abutment. The locations of the leveling rods are shown in Figure 6.

6.2 Lateral Movement

The term "lateral movement," unless otherwise specified, was referred to the total

expansion along the perimeter of the structure. Elastic springs were wrapped around the

circumference of the outer pier and three sides (north, west and south) of the abutment at

selected heights. By measuring the elongation of the elastic spring, the lateral movement of

the outer pier and the abutment was obtained. The heights at which the elastic springs were

installed on the outer pier were 2.1 m, 4.6 m, and 6.6 m from the base. For the abutment,

the elastic springs were located at 5.2 m, 6.0 m and 6.4 m from the base. The locations of

28

29

Fig~ 5 InStrumentation for Verticw and Lateral Movements

I-- 2.45 '" .. I.. 2.74 '" -I" 2.74 '" + 2.74 '"

r-

1-+ 2.10 "'-

Qj .p

E Qj E E E '-"- u co co ru In c: - "- .... .; 0 Ifi .; Lri u

PJl6

P02

Outer Pier Center Pier

Fig.6 Locations of the Leveling Rods

_1--'1::2 A04

-.-

f-;08 A~

concrete E po.d

co -Ifi £:

\0 -" h07 A~

- ,..... An-

Abu t Ment

-.:1 AOl () ,

111 .. '-111

P02

'" o

GIRDERS

Elastic sp Elo.stlc springs

:-- SP03. Lo.,.):'er C CI?

A03 Loyer C . c= LL £: £: Lo.,.):'er B ~ r-- SP02 ~ CI? ru CIJ ci 0

(]) (]) Lo.~er",A c c L.-. Spot '" .Cl Cl D D

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+' +' ci C C .. .. Cl)

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£: AO Lo.yer A .. -u

~ Relnfo.rcel"lent a with strain 90.9"s <0-

- - J; .. Relnfo.rcel"lent Relnforcel"lent ~

with stro.ln g< .. s with stro.ln go.ge

, ,

OUTER PIER CENTER PIER ABUTMENT

Fig.7 Locations of the Reinforcements with Strain Gages and the Elastic Springs

SP)

,

Legen( .J:l. Stra

SA ELcs

"" ...

the elastic springs (denoted as SP for the outer pier and SA for the abutment) are shown in

Figure 7.

6.3 Strains in Reinforcement

High elongation strain gages, manufactured by Measurements Group, Inc. (type EP-

08-250BG-120), were used to measure the strain distribution in the geotextile

reinforcement. A total of six strain gages were mounted along the fill and the warp

directions of each instrumented sheet of reinforcement for the outer and center piers. There

were three sheets of instrumented geotextile reinforcement located at 2.0 m, 4.5 m, and 6.5

m from the base in the outer pier and 1.9 m, 4.3 m, and 6.5 m from the base in the center

pier. The abutment had three sheets of instrumented geotextile reinforcement with six

strain gages along the fill direction on each sheet. They were located at carrying 5.1 m, 5.9

m, and 6.5 m from the base. The locations of the reinforcement sheets with strain gages are

shown in Figure 7.

Each strain gage was glued to the geotextile only at the two ends to avoid

inconsistent local stiffening of the geotextile due to the adhesive. The strain gage

attachment technique was developed at the Reinforced Soil Research Center of the

University of Colorado at Denver. The gage was first mounted on a 25 mm by 76 mm

patch of a light weight nonwoven geotextile. The light-weight geotextile patch (with a

strain gage and wax) was then attached to the woven geotextile reinforcement at selected

locations. A microcrystalline wax material was applied over the gage to protect it from soil

moisture. Figure 8 shows a strain gage mounted on a light-weight nonwoven geotextile

32

patch and attached to the woven reinforcement.

Due to the presence of the light-weight geotextile patch, calibration is needed.

Calibration tests were performed to relate the strain obtained from the attached strain gage

to the actual strain of the reinforcement. The calibration curves along the fill and the warp

directions of the woven geotextile reinforcement used in the load test are shown in Figure 9

and Figure 10, respectively.

33

34

Fig. 8 Strain Gage Attachment

7.00,1--------------______ -,

6.00 . / +

++ + - ++ + + ~ -; 5.00 ++ + .5 ++ + + .<: u .. + :&

+ ~ 4.00 :& .. .<: -E ,g

3.00 c :g rn .. DI

~ 2.00

.>c

1.00

0.00 ~I'~-_--_--_-____:_=_-__:_:::_-_::;--~ 0.00 1.uu 2.00 3.00 4.00 5.00 6.00 7.00

Measured Strain from Strain Gage (%)

Fig. 9 Strain Gage Calibration in the Fill Direction of the Reinforcement

7.00 ,1--------------------,

6.00

-~ • -; 5.00 c E u .. E rn .... 4.00 :& .. .<: -E ,g c 3.00

~ rn .. Cl j 2.00

1.00

0.00 -I"I'--_--_--_-_--~--_-__I 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00

Measured Strain from Strain Gage rk)

- Fig. 10 Strain Gage Calibration in the Warp Direction of the Reinforcemen1

w

'"

Chapter 7 RESULTS OF THE FIRST-STAGE LOAD TEST

7.1 Short-Term Behavior

The measured short-tenn vertical and lateral displacements of the abutment and the

pier, as well as the measured strains in the geotextile reinforcement soon after the load

application are presented in the following sections. In addition, discussions of the

measured results are presented.

7.1.1 Vertical and Lateral Displacements

Figure 11 and Figure 12 show the applied load versus displacement relationships of

the abutment in the vertical and lateral directions, respectively. The vertical displacements

were fairly unifonn along the two axial directions. The maximum vertical displacements at

1,170 kN were 27.1 mm at the top and 5.2 mm at the base. The maximum lateral

movement at 5.2 m from the base was 14.3 mm.

Figure 13 and Figure 14 show the applied load versus displacement relationships of

the outer pier in the vertical and lateral directions, respectively. Similar to the abutment,

the vertical displacements were fairly unifonn along the two axial directions. The

maximum vertical displacements at 1,170 kN (232 kPa pressure) were 36.6 mm at the top

and 6.1 mm at the base. The maximum lateral movement at 4.6 m from the base was

36

0 0.0

5.0

10.0 -E E 15.0 --c ~ 20.0

Q) u .!! 25.0 Q. I/) -o 30.0 iii u 1:: 35.0 Q)

> 40.0

45.0 1

50.0

Applied Load (kN) 500 1000 1500 2000

--AD1 --AD2 -+-AD3 --A04 --ADS --AD6 --+-AD7 -ADa

(See Figure 6)

Fig. 11 Vertical Disp1acement versus Applied Load Relationships of the Abutment

2500

w ....

0 0.0

5.0

10.0

-E 15.0 E --C 20.0 CI)

E CI) CJ 25.0 CIS Q. IIJ

30.0 ~ i5 -e! CI)

35.0 ~ 1U -'

40.0

45.0

50.0

Applied Load (kN) SOO 1000 1500 2000

I--SA01 -G- SA02,SA03

(See Figure 7)

Fig. 12 Lateral Displacement versus Applied Load Relationships of the Abutment

2500

'" 00

0 0.0

5.0

10.0 -E E 15.0 --c ~ 20.0 CI) (.) .!!! 25.0 Q. 1/1

C 30.0 iii (.)

:e 35.0 CI)

> 40.0

45.0 j 50.0

Applied Load (kN) 500 1000 1500 2000

--P01 -o-P02 --P03 --P04 --pos --P06

(See Figure 6)

Fig. 13 Vertical Displacement versus Applied Load Relationships of the Outer Pier

2500

'" '"

0 0.0

5.0

10.0 -E 15.0 E --C

CD 20.0 E CD 0

25.0 tIS Q. II) -C 30.0

e CD 35.0 -tIS

...J

40.0

45.0

50.0

Applied Load (kN) 500 1000 1500 2000

--SP01 -D-SP03 -Ir-SP02

(See Figure 7)

Fig. 14 Lateral Disp1acement versus Applied Load Relationships of the Outer Pier

2500

..,. o

12.7mm.

Figure 15 shows the vertical and lateral movements of the outer pier and the

abutment at the applied load of 1,170 kN. Table 2 summarizes the maximum vertical and

lateral movements of the outer pier and the abutment. It is shown that the vertical

movement of the foundations for the outer pier and the abutment was about the same (6.1

mm for the pier, 5.2 mm for the abutment). The different magnitudes of the vertical

movement on top of the pier and the abutment were, therefore, a result of the different

amounts of vertical compression of the structures upon loading. The maximum vertical

movement of the pier was 0.48% of its height. Such a value was higher than that of the

Tumer-Fairbank's load test which was 0.30% (without prestraining) at the same applied

pressure. This may be attributed to the much lower compaction effort on the outer pier.

The maximum lateral movements of the pier and the abutment were comparable (12.7 mm

in the pier, 14.3 mm in the abutment).

The maximum differential settlements at the bases of the abutment and the pier

were 5.2 mm and 5.5 mm, respectively. The 0.15-m thick concrete pads at the base and the

geosynthetic-reinforced soil foundation appeared to be a competent platform for the

abutment and the pier.

From the applied load versus displacement relationships of the abutment and the

pier (Figures 11, 12, 13 , and 14), the bearing capacity of the structures can be determined

based on the tolerable vertical and lateral deformation upon loading. For example, the

41

(~/~1~(~(~

-I- t , 24 ~~ 3 ~~ ~ ____ I .1 8 ~~ . E 28 MM 1l MM -t-

8 ~~~ / ___________ __

14 ~~L~~------11---I .~f.I-----__tt_j 13 ~ ~ L

,.. - f-

6 ~~ -rc ,

_r I I

OUTER PIER ABUTMENT

Fig. IS Vertical and Lateral Movements of the Outer Pier and the Abutment at 1,170 kN

o rI

.0-N

43

Structure Maximum Vertical Movement Maximum Lateral Movement

(mm) (mm)

Foundation Structure Total

Outer Pier 6.1mm 30.5mm 36.6mm 12.7 mm

Abutment 5.2mm 21.9mm 27.1 mm 14.3 mm

Table 1 Maximum Vertical and Lateral Movements of the Outer Pier and the Abutment at 1.170 kN

bearing capacity of the abutment at the tolerable vertical settlement of 12.7 mm (0.5 in.) is

limited to 146 kPa (see Figure 11).

After the load of 1,170 kN was applied, predominantly vertical hairline cracks in the

facing blocks were observed along the length and the width directions of the outer pier and

the face of the abutment. It was not clear when was the first crack developed. With time,

however, the cracks increased both in the number and in the width. It is recommended the

geosynthetic reinforcement be wrapped around at the facing as in the last four layer of

reinforcement of the abutment to prevent losing of the backfill through the cracks.

7.1.2 Strains in Reinforcement

Figure 16 shows the strain distributions in the fill direction along the length of the

three instrumented sheets of reinforcement in the abutment. The largest strains were on the

order of 0.15% to 0.18% at the applied load of 1,170 kN. The largest strains occurred

adjacent to the facing (the center of bearing plates was only 0.3 m from the back face of the

facing blocks) and decreased toward the other end. The strains were nearly zero at 2.5 m

from the facing.

The reinforcement strains in the fill direction of the outer pier were on the order of

0.2% to 0.4% at the applied load of 1,170 kN (232 kPa pressure). Note that such a

magnitude of reinforcement strain was similar to that measured in the Turner-Fairbank's

load test at the same applied pressure. This implies that at the same applied pressure the

lateral displacement of the outer pier and the Turner-Fairbank pier was comparable.

44

45

Reinforcement Strain Distribution of the Abutment, Layer A

0.50

0.40 I~M867kN,1 ~

-D-M 1170kN 0.30

c '! 0.20 ~ en

I1J...... 0.10 .""':':::::"-:"1:6 ....... . 0.00

0 1 2 3

Distance from the Facing Block (m)

Reinforcement Strain Distribution of the Abutment, Layer B

0.50

0.40 ........ M867kN

~ -o-At 1170 kN

0.30 c '! 020 Iii

0.10

0.00 0 1 2 3

DI.tance from the Facing Block em)

Reinforcement Strain Distribution of the Abutment, Layer C

0.50

0.40 ........ M 867 kN

~ -0-At 1170 kN

0.30 c ! 0.20 Iii --0.10 .-~

0.00 0 2 3

Distance from Ule Facing Block (m)

Fig. 16 Reinforcement Strain Distributions in the Abutment

Compared the largest strains in the abutment and the outer pier (on the order of

0.2% to 0.4%) to the rupture strain (18%), the safety margin appeared to be very high

against rupture failure of the reinforcement. However, the load carrying capacities of both

structures may not be governed by the rupture failure of the reinforcement. Slippage

between the backfill and the reinforcement or the shear failure of the backfill may occur

first.

7.2 Long-Term Behavior under 1,170 kN Load

Time dependent behavior of the abutment and pier -- including vertical

displacements, lateral displacements, and reinforcement strains -- under a sustained load of

1,170 kN is presented in the following sections. Discussion of the measured results are

also presented.

7.2.1 Vertical and Lateral Creep Displacements

Figure 17 and Figure 18 show, respectively, the vertical and lateral displacements

versus time relationships of the abutment under the sustained load of 1,170 kN. The

maximum vertical displacements at the top and the base after 70 days were 18.3 mm and

6.7 mm, respectively. The maximum lateral displacement was 14.3 mm after 70 days.

Most of the maximum vertical and lateral displacements (12 mm and 13 mm, respectively)

occurred in the flIst 15 days.

46

0 10 0

10

- 20 E E -- 30 c II)

E II) 40 u as Q. I/) 50 .-C Q. II) 60 e 0 'ii 70 u I .-t:: II)

80 > 90

100

Elapsed Time (day) 20 30 40 50 60 70 80 90

---A01 -a-A02

---A03 --A04 --AOS --A06 -t-A07 -A08

(See Figure 6)

Fig. 17 Vertical Creep Displacement versus Time Re1ationships of the Abutment

100

... ...,

0 10 0

10

- 20 E E -- 30 C CD E CD 40 U ns C. en 50 -C c.. CD 60 ~ 0

~ 70 CD -ns ..J 80

90

100

Elapsed Time (day) 20 30 40 50 60 70 80 90

--SA01 --e--SA02 --SA03

(See Figure 7)

Fig. 18 Lateral Creep Displacement versus Time Relationships of the Abutment

100

~ co

Figure 19 and Figure 20 show, respectively, the vertical and lateral displacements

versus time relationships of the outer pier under the sustained load of 1,170 kN. The

maximum vertical displacements at the top and the base after 70 days were 61.6 mm and

5.2 mm, respectively. The maximum lateral displacement was 59.5 mm after 70 days.

Similar to the abutment, a large portion of the maximum vertical and lateral displacements

(48 mm and 46 mm, respectively) also occurred in the first 15 days. The maximum vertical

and lateral displacements of the outer pier were about four times as large as those of the

abutment. This is most likely due to poor compaction by a light weight vibrating plate used

during construction.

Figure 21 shows the average vertical creep rate of the top loading pad versus time

relationships of the outer pier and the abutment plotted on a log-log scale. It is shown that,

for the most part, the vertical creep rate of both structures reduced nearly linearly (on a log­

log scale) with time. The vertical creep rates in the abutment reduced from 2.2 mmlday

after 3 days to 0.03 mmldayafter 70 days in the abutment. During the same period of time,

the creep rate reduced from 7.5 mmlday to 0.1 mmlday in the outer pier. At around 25

days, both creep rates of the pier and the abutment significantly increased as shown in

Figure 21. This behavior is attributed to softening of the frozen backfill due to a

temperature increase following an extended period of freezing temperatures.

Extrapolations of the average vertical creep rates were drawn as the shaded areas in Figure

21. The extrapolation may be used to obtain approximate creep rates beyond the

measurement period. For instance, after a year, the vertical creep rates of the abutment and

the outer pier were in the ranges of 0.003 mmlday to 0.008 mmlday and 0.012 mmlday to

49

0 0

10 ~'-,I

- 20 E E -- 30 c CII E CII 40 U I tIS C. ,!g 50 C Q. CII 60 e 0 iii 70 U :e CII 80 >

90

100

Elapsed Time (day) 10 20 30 40 50 60 70 80 90

: :a::; ;;: - -----c ---.. M __ K SE iii )f

I---P01 -e-P02 ---P03 --P04 --pos ---POS

\.'\. (See Figure 6)

Fig. 19 Vertical Creep Displacement versus Time Relationships of the Outer Pier

100

l.n o

0.0

10.0 -E 20.0 E ..... .. C

30.0 II)

E II) u 40.0 ca -g. II) .-C 50.0 g. II)

f 60.0 0 -E 70.0 S ca ..J

80.0

90.0

100.0

Elapsed Time (day) 0 10 20 30 40 50 60 70 80

Fig. 20 Lateral Creep Displacement versus Time Relationships of the Outer Pier

90

__ SP01

-o-SP02

--.er-SP03

(See Figure 7)

100

V1 -

-iU' ~ E E -oS G. Q, Q)

f 0 Q) C)

e Q)

~

10000 I I _II I I IIIIIII I I IIIIIII 1.000

0.100

0.010

I.

'~

~

~

~,,~

I 1IIIIIIr~\J 11111111

,00 1 __ Abutment 1 1000

1'1 I I 1 ! 0.001 An

1 I V

Elapsed Time (day) 1-0-Outer Pier

Fig.ll Average Vertical Creep Rate at Top of the Outer Pier and the Abutment \.n to>

0.06 mmlday, respectively.

7.2.2 Creep Strains in Reinforcement

Figure 22 shows the reinforcement creep strain distributions in layers A, B, and C

(see Figure 7) of the abutment after 10, 25, and 70 days. The creep strain distributions

were somewhat more uniform than the short-term reinforcement strain distribution. After

70 days, the maximum creep strains in layers A, B, and C were 0.30%, 0.75% and 0.38%,

respectively. Note that such maximum creep strains were also far from the rupture strain

(18%) of the reinforcement.

Figure 23 shows the reinforcement creep strain distributions in layer A (both the

warp and fill directions) and layer C (the warp direction) of the outer pier after 10, 25, and

70 days. A uniform strain distribution was assumed in the reinforcement of the outer pier.

The average strain of each layer was shown in Figure 23. After 70 days the average creep

strains of layer A were 0.20% and 0.46% in the fill and warp directions, respectively, and

0.53% in the warp direction of the layer C. The higher creep strains in the warp direction

was mainly due to the fact that the geotextile is nearly twice as likely to creep in its warp

direction (Ketchart and Wu, ) 996).

From the average strains in layer A of the outer pier, the lateral creep displacements

were calculated and compared to the measured lateral creep displacements. The

comparison is shown in Figure 24. It is seen that the calculated lateral creep displacements

53

(from the strain distributions) were In very good agreement with the measured

displacements.

54

~ 1.00 c 0.80 ! 0.60

0.40 D. 0.20

~ 0.00 0.0

l 1.00 c 0.80 ! 0.60

0.40 ~ 0.20 u 0.00

~ 1.00 c 0.80 ! 0.60 en 0.40

"" ! 0.20 u 0.00

0.0

0.0

lie

e

Reinforcement Creep Strain Distribution of the Abutment, Layer A

0.5

__ 10 days

-!i.l-25 days

-lIE-70 days

. -'!'

1.0 1.5 2.0 2.5

Distance from the Facing Block (m)

Reinforcement Creep Strain Distribution of the Abutment, Layer B

__ 10 days

-G-25days

~ -lIE-70 days

~

3.0

0.5 1.0 1.5 2.0 2.5 3.0

Distance from the Facing Block (m)

Reinforcement Creep Strain Distribution of the Abutment, Layer C

__ 10 days

--D-25days

-lIE-70 days

---0.5 1.0 1.5 2.0 2.5

Distance from the Facing Block (m)

r-

3.0

Fig. 22 Reinforcement Creep Strain Distributions in the Abutment

55

~

~

Reinforcement Creep Strain Distributions of the Outer Pier, Layer A, Warp Direction

1.00 1 ----------------;:::;::==1 .3 days t;10days

A70days

0.80

0.60 0.46%

- -D. 0.40

5

~

~ Co m e 0

~ c

~

0.20 ~

0.00

0.0

1.00

0.80

0.60

0.40

0.20

0.00

0.0

_III _ 0.16%

0:08%--!I

- ----- - -- ..- - -

0.5 1.0 1.5 2.0 2.5

Distance from the Facing Blocks (m)

Reinforcement Creep Strain Distributions of the Outer Pier, Layer A, Fill Direction

0.4

.3 days rM 10 days

&70 days

-----A__ __ __ __ 0.20% _ __ __ • __ _ 0.10%

-- - e= - - 0.05%

0.6 1.2

Distance from the Facing Blocks (m)

Reinforcement Creep Strain Distributions of the Outer Pier, Layer C, Warp Direction

1.00,---------------r----n .3 days

0.80

0.60 0.53%

~- -- -

«< 10 days

&70 days

Co 0.40

5 IE 0.23% 0.20

0.03% III

• 0.00 .f-='-'='--'i='-'=o...=='-4=r=='--==r'--=='--="l 0.0 0.5 1.0 1.5 2.0 2.5

Distance from the Facing Blocks (m)

Fig. 23 Reinforcement Creep Strain Distributions in the Outer Pier

56

0 0

10

- 20 E E -... 30 C CI)

E CI) 40 0 C'CI

C. II> 50 .-C Q, CI)

~ 60

0

~ 70

CI) ... C'CI 80 -'

90

100

Elapsed Time (day)

10 20 30 40 50 60 70 80 90

--Calculated --D- Measured

Fig. 24 Calculated versus Measured Lateral Creep Displacements of the Outer Pier

100

U>

"

Chpater 8 SUMMARY AND CONCLUSIONS

A GRS bridge abutment and two GRS bridge piers were constructed inside a 3.5-m

deep pit. The structures were constructed with a "road base" backfill reinforced with layers

of a woven geotextile. Hollow-cored concrete blocks were used as facing. One of the piers

(i.e. the outer pier) and the abutment, both 7.6 m in height, were load tested. The load was

applied using concrete barriers stacked in seven layers over three steel bridge girders. A

total load of 2,340 kN, corresponding to 232 kPa pressure, was applied. The pier and the

abutment were instrumented with metal pipes and elastic springs to monitor the vertical and

lateral movement of the facing, and strain gages to monitor deformation of the

reinforcement. The fmdings are summarized as follows:

I . Construction of the GRS pier and abutment is indeed rapid and simple.

2. Load carrying capacities of the pier and the abutment were higher than the 200 kPa

maximum pressure suggested by the FHW A Demo 82 (1996).

3. The displacements at 1,170 kN of the pier and the abutment were comparable. The

maximum vertical displacement was slightly higher in the outer pier than in the

abutment. The maximum vertical displacements were 27.1 rnrn in the abutment and

36.6 rnrn in the outer pier, corresponding, respectively, to 0.35% and 0.48% of the

structure height. The maximum lateral displacement in the abutment was somewhat

higher than that in the outer pier. The maximum lateral elongation of the perimeter

were 4.3 rnrn in the abutment and 12.7 rnrn in the outer pier.

58

4. The ratio of the vertical movement to the structure height at 232 kPa of the outer pier

(0.48%) was higher than that of the Turner-Fairbank pier (0.30%) at the same applied

pressure. This may be attributed to the much lower compaction effort on the outer

pier. The reinforcement strains in the fill direction of the outer pier and the Turner­

Fairbank pier, however, were on the same order of magnitude (0.2% to 0.4%). This

implies that the lateral movements of both piers are comparable.

5. Under a sustained load of 1,170 kN for 70 days, the creep displacements in both

vertical and lateral directions of the outer pier were about four times larger than those

in the abutment, due to lower compaction effort of the outer pier. The maximum

vertical creep displacement was 61.6 mm in the outer pier, and 18.3 mm in the

abutment. The maximum lateral creep displacement was 59.5 mm in the outer pier

and 14.3 mm in the abutment.

6. A significant portion of the maximum vertical and lateral creep displacements of the

pier and the abutment occurred in the first 15 days. At 15 days, the maximum

vertical and lateral creep displacements were about 70% to 75% of the creep

displacements at 70 days in respective directions.

7. Creep deformation of the structures decreased with time. The vertical creeprates

reduced nearly linearly (on log-log scale) with time. The creep rates of the outer pier

(7.5 mm1day after 3 days and 0.1 mm1day after 70 days) were higher than those of the

abutment (2.2 mm1day after 3 days and 0.03 mm1day after 70 days).

8. Hairline cracks of the facing blocks occurred in the outer pier and the abutment due

to the lateral bulging and the downdrag force due to the friction between the backfill

and the facing blocks. This may be alleviated by providing flexible cushions between

59

vertically adjacent blocks.

9. The maximum strains in the reinforcement were less than 1.0%. Compared to th.:

rupture strain of the reinforcement of 18%, the safety margin against rupture of

reinforcement appeared to be very high.

10. The calculated lateral displacements from the reinforcement strain distribution were

in very good agreement with the measured lateral displacements.

II . With the less stringent construction condition (using a light-weight vibrating

compaction plate), the outer pier showed about 1.5 times larger vertical displacement­

to- height ratio than the Tumer-Fairbank pier; whereas the lateral displacements were

similar.

60

REFERENCES

Adams, M. (1997), "Performance of a Prestrained Geosynthetic-Reinforced Soil Bridge

Pier," Keynote Lecture, Mechanically Stabilized Backfill, A. A. Balkema Publisher,

Netherlands.

FHW A Demonstration Project 82 (1996), "Mechanically Stabilized Earth Wall and

Reinforced Soil Slopes Design and Construction Guideline," Pub. No. FHW A- SA-96-

071, Federal Highway Administration, US Department of Transportation

Ketchart, K. and Wu, IT.H. (1996), "Long-Term Performance Tests of Soil-Geosynthetic

Composites," Report No. CDOT-CTI-96-1, Colorado Department of Transportation.

61

62

ACKNOWLEDGMENTS

This project is part of an ongoing joint research effort of the Colorado Department of

Transportation, Reinforced Soil Research Center of the University of Colorado at Denver, and Turner­

Fairbank Highway Research Center of the Federal Highway Administration to develop design and

construction guidelines for GRS bridge support system. The authors wish to acknowledge the

dedication of Mr. Robert K. Barrett for construction and making it happen, to express their gratitude to

Mr. Charles Bennett and the construction crews of the Colorado Department of Transportation, to Mr.

Michael Adams of Turner-Fairbank Highway Research Center of the Federal Highway Administration

for insightful discussions and his participation in the first-stage load test, to Mr. Darnin Shi for

installing the strain gages.