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
A02 M Cl g Loyer B '" n g " III III (\J
+' +' ci C C .. .. Cl)
" £: C .. .. D u U d ~ ~ a. a a III
<0- <0-J; .<: +' .. .. c ~ ~ OJ
£: 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.