Citation
Field performance of a new reinforced soil retaining wall with full-height facing and yielding connection

Material Information

Title:
Field performance of a new reinforced soil retaining wall with full-height facing and yielding connection
Creator:
Ma, Christina Cheng-Wei
Publication Date:
Language:
English
Physical Description:
90 leaves : illustrations ; 28 cm

Subjects

Subjects / Keywords:
Retaining walls -- Design and construction ( lcsh )
Retaining walls -- Design and construction ( fast )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (leaf 90).
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Christina Cheng-Wei Ma.

Record Information

Source Institution:
University of Colorado Denver
Holding Location:
Auraria Library
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
45545553 ( OCLC )
ocm45545553
Classification:
LD1190.E53 2000m .M3 ( lcc )

Full Text
FIELD PERFORMANCE OF A NEW REINFORCED SOIL
RETAINING WALL WITH FULL-HEIGHT FACING
AND YIELDING CONNECTION
by
Christina Cheng-Wei Ma
A thesis submitted to the
University of Colorado at Denver
in partial fulfillment
of the requirements for the degree of
Master of Science
Civil Engineering
2000

W...,
*


This thesis for the Master of Science
degree by
Christina Cheng-Wei Ma
has been approved
by
~!/zo /-mo
Date


Ma, Christina Cheng-Wei (M.S., Civil Engineering)
Filed Performance of a New Reinforced Soil Retaining Wall with Full-Height
Facing and Yielding Connection
Thesis directed by Professor Jonathan T. H. Wu
ABSTRACT
A new retaining wall was designed and constructed by the Colorado
Department of Transportation (CDOT) in 1996 for the ramp connecting
Northbound 1-25 and 1-70. A new construction technique that uses an
Independent Full-height Facing (IFF) panel in front of a reinforced soil mass was
employed. The new construction technique was adopted because it does not
require over-excavation in front of the wall. This feature allows the traffic to
remain open during construction and alleviate the need to deal with excavation
and disposal of contaminated subsoil. Two sections of the retaining wall were
instrumented to monitor the performance during and after construction. A total of
48 survey tagets (24 for each Station), 2 inclinometers, 32 wire mesh strain gages,
21 rebar strain meters, and 16 themistors were employed. Some of the strain
gages were malfunctioned before or during construction.
A study was undertaken to synthesize the measured data and to evaluate
the performance and design assumptions of the retaining wall. This report
describes the project and the instrumentation, presents the measured data and data
in


reduction, synthesizes the measured data (including wall displacements by
surveying, wall rotation by the inclinometers, strains in the wire mesh
reinforcement, and strains in the rebar face anchors), and assesses the design
assumptions. Judicious judgements had to be made in the interpretation of the
measured data because the information on the measured data was incomplete and
some of the measurements were not entirely stable. The report discusses the
wall performance in detail based on the synthesized information. Design
implications, including initial setback of the facing panels, reinforcement strength
requirement, and forces on the facing panels were also addressed.
This abstract accurately represents the content of the candidates thesis. I
recommend its publication.
Signed

IV


CONTENTS
Figures.................................................................. vii
Tables.................................................................... xi
Chapter
1. Introduction............................................................ 1
1.1 Problem Statement................................................... 1
1.2 Study Objectives.................................................... 3
1.3 The Independent Full-height Facing (IFF) Reinforced Soil Retaining
Wall............................................................... 4
1.4 Contents of the Report.............................................. 7
2. Project Description..................................................... 8
2.1 The IFF Reinforced Soil Retaining Wall.............................. 8
2.2 Construction Method................................................ 11
2.3 Fill History....................................................... 13
3. Instrumentation........................................................ 16
3.1 The Instruments................................................... 16
3.2 Layout of Instruments.............................................. 17
3.3 Data Reduction.................................................... 24
4. Measured Results and Discussion of Results.............................28
v


4.1 Measured Data in Excel.........................................28
4.2 Wall Movement................................................. 28
4.2.1 Surveying......................................................28
4.2.2 Inclinometer...................................................41
4.3 Forces in Wire Mesh Reinforcements.............................50
4.4 Forces on Facing Panels........................................70
5. Summary and Conclusions.......................................... 83
5.1 Summary........................................................83
5.2 Findings and Conclusions...................................... 85
References.......................................................... 90
vi


FIGURES
Figure
1.1 Location of Project................................................... 2
1.2 The independent Full-height Facing (IFF) Reinforced
Soil Retaining Wall.................................................... 5
2.1 Typical Cross Section of Retaining Wall............................... 9
2.2 Completed IFF MSE Wall............................................... 10
2.3 Facing Panels Rested in Trench and Supported by Temporary Bracing.... 12
2.4 Fill History of Station 3116......................................... 14
2.5 Fill History of Station 3119......................................... 15
3.1 Layout of Face Anchor Strain Meters and Inclinometers
for Station 3116.......................................................18
3.2 Layout of Face Anchor Strain Meters and Inclinometers
for Station 3119.......................................................19
3.3 Layout of Wire Mesh Strain Gages for Station 3116.....................20
3.4 Layout of Wire Mesh Strain Gages for Station 3119.................... 21
3.5 Layout of Wire Mesh Strain Gages at Different Elevations
For Station 3116.......................................................22
3.6 Layout of Wire Mesh Strain Gages at Different Elevations
for Station 3119...................................................... 23
Vll


3.7 Load-Deformation Testing of Wires Used for Reinforcement...........26
4.1 (a) Cumulative Change in Elevation vs. Time for
Station 3116 at H= 1 ft.........................................29
4.1 (b) Cumulative Change in Elevation vs. Time for
Station 3116 at H=4ft...........................................30
4.1 (c) Cumulative Change in Elevation vs. Time for
Station 3116 at H=7ft...........................................31
4.2 Average Cumulative Change in Elevation vs. Time for Station 3116...32
4.3 (a) Cumulative Change in Distance vs. Time for
Station 3116 at H=lft...........................................34
4.3 (b) Cumulative Change in Distance vs. Time for
Station 3116 at H=4ft...........................................35
4.3 (c) Cumulative Change in Distance vs. Time for
Station 3116 at H=7ft...........................................36
4.4 Average Cumulative Change in Distance vs. Time for Station 3116....37
4.5 (a) Cumulative Change in Elevation vs. Time for
Station 3119 at H= lft.......................................... 38
4.5 (b) Cumulative Change in Elevation vs. Time for
Station 3119 at H=4ft........................................... 39
vm


4.5 (c) Cumulative Change in Elevation vs. Time for
Station 3119 at H=7ft............................................. 40
4.6 Average Cumulative Change in Elevation vs. Time for Station 3119......42
4.7 (a) Cumulative Change in Distance vs. Time for
Station 3119 at H=lft.............................................43
4.7 (b) Cumulative Change in Distance vs. Time for
Station 3119 at H=4ft............................................. 44
4.7 (c) Cumulative Change in Distance vs. Time for
Station 3119 at H=7ft.............................................45
4.8 Average Cumulative Change in Distance vs. Time for Station 3119.......46
4.9 Wall Deflection Rate vs. Time for Station 3116........................47
4.10 Wall Deflection Rate vs. Time for Station 3119.......................48
4.11 (a) Strains in Wire Mesh vs. Time for Station 3116 at H=lft.........51
4.11 (b) Strains in Wire Mesh vs. Time for Station 3116 at H=4ft........ 52
. 4.11 (c) Strains in Wire Mesh vs. Time for Station 3116 at H=7ft........ 53
4.11 (d) Strains in Wire Mesh vs. Time for Station 3116 at H=11ft........ 54
4.12 Strains in Wire Mesh vs. Time for Station 3119
at H=lft, 3ft and 5ft................................................ 55
4.13 (a) Forces in Wire Mesh vs. Time for Station 3116 at H=1 ft.........57
4.13 (b) Forces in Wire Mesh vs. Time for Station 3116 at H=4ft..........58
IX


4.13 (c) Forces in Wire Mesh vs. Time for Station 3116 at H=7ft...............59
4.13 (d) Forces in Wire Mesh vs. Time for Station 3116 at H= lift.............60
4.14 (a) Forces in Wire Mesh vs. Time for Station 3119 at H=lft...............62
4.14 (b) Forces in Wire Mesh vs. Time for Station 3119 at H=3ft...............63
4.14 (c) Forces in Wire Mesh vs. Time for Station 3119 at H=5ft...............64
4.15 (a) Forces along the length of Wire Mesh for Station 3116 at H=lft... 65
4.15 (b) Forces along the length of Wire Mesh for Station 3116 at H=4ft...66
4.15 (c) Forces along the length of Wire Mesh for Station 3116 at H=7ft...67
4.15 (d) Forces along the length of Wire Mesh for Station 3116 at H=11 ft...68
4.16 (a) Forces in Rebar vs. Time for Station 3116 at H=0ft.................. 72
4.16 (b) Forces in Rebar vs. Time for Station 3116 at H=6ft.................. 73
4.16 (c) Forces in Rebar vs. Time for Station 3116 at H=11 ft................ 74
4.17 (a) Forces in Rebar vs. Time for Station 3119 at H=0ft.................. 76
4.17 (b) Forces in Rebar vs. Time for Station 3119 at H=3ft.................. 77
4.17 (c) Forces in Rebar vs. Time for Station 3119 at H=7fit................. 78
4.18 Average Forces in Rebar vs. Time for Station 3119......................79
4.19 Surface of Reinforced Fill in Full-Scale Test after
Removal of Facing Panel................................................ 82
x


TABLES
Tables
2.1 Typical Setbacks..................................................... 13
3.1 Three-Character Labeling for Station 3116 Mesh Strain Gages...........24
4.1 Average Rebar Forces at Different Heights for Station 3116............75
4.2 Average Rebar Forces at Different Heights for Station 3119........... 80
5.1 Maximum Rebar Forces at Different Heights for Station 3116............88
5.2 Largest Change in Rebar Forces at Different
Heights for Station 3119............................................89
xi


1. Introduction
1.1 Problem Statement
In 1996 the Colorado Department of Transportation (CDOT) constructed a
new retaining wall for the ramp connecting Northbound Interstate-25 to Interstate-
70 (see Figure 1.1). Since the new retaining wall was an extension of an existing
cantilever reinforced concrete retaining wall, it was deemed necessary for the new
retaining wall to bear the same appearance as the existing wall which had full-
height grooved concrete facing.
A construction technique that uses an independent full-height facing panel
in front of a reinforced soil mass was adopted. This is a patented technique
owned by the Colorado Department of Transportation. The cost per square foot
of facing for the construction technique was estimated to be around $20, which is
about Vi of the cost of a reinforced concrete cantilever wall. The selection of this
technique was, however, based primarily on the fact that little or no excavation in
front of the wall is needed. The benefits of this are two-folds. Firstly, the wall is
situated along a very busy section of 1-25, little or no excavation means minimal
or no disruption of the traffic. Secondly, the subsoil on the project site was
known to have been contaminated in the past. Excavation of the contaminated
soil, if needed, would have to involve undue delay for the construction.
Two sections of the retaining wall, each 56ft wide, were instrumented
1


Figure ]. ] Location of Project


to monitor the performance during and after construction. These sections were
designated as Station 3116 and Station 3119. Each test section was composed of
six 8-fit wide facing panels and two 4ft wide facing panels. Typical panel heights
of Stations 3116 and 3119 were 15.25ft and 12.375ft.
1.2 Study Objectives
The objectives of this study were two-folds. The first objective was to
organize the measured data. There were stacks of paper containing information
related to the instrumentation and measured data. Besides, a number of persons
were involved in different stages of the project and some are no longer with
CDOT. Proper organization and interpretation of the measured data gathered for
the project, therefore, became a rather challenging task. The second objective
was to synthesize the measured data and assess the design assumptions. The
measured data were synthesized to gain a better understanding of the performance
of the wall. Whenever applicable, the measured data were compared with the
design value to assess the design assumptions. As some of the measured data
were not entirely stable, judicious judgements had to be made to achieve this
objective.
3


1.3 The Independent Full-height Facing (IFF)
Reinforced Soil Retaining Wall
As shown in Figure 1.2, the IFF reinforced soil wall system has three
major components: full-height reinforced concrete panels (as the wall facing),
reinforced soil mass (comprises the backfill and layers of reinforcement), and face
anchors (to attach the facing panel to the reinforced soil mass). Note that the
face anchor can take many different forms. The one shown in the Figure is a
straight shaft anchor with circular anchor plates.
To construct an IFF reinforced soil retaining wall, the facing panel is first
erected with the support of temporary bracing. The reinforced soil mass is then
constructed behind the facing by placing layers of the reinforcement in the
backfill at prescribed vertical spacing. The face anchors are installed at selected
heights to connect the facing panel to the reinforced soil mass. The temporary
bracing is removed after the facing is securely attached to the reinforced soil
mass.
The IFF wall system has a number of distinct characteristics over the
conventional cantilever reinforced concrete retaining wall. These characteristics are:
Construction of the IFF wall is rapid and relatively easy. Construction
typically requires little or no over-excavation. Construction does not require
on-site concrete formwork.
4


Sure 1.2
file Indi
ep"de Pui,..

0rC*S *'^ing Wall
5


- The IFF wall, although constructed with rigid concrete facing, is more flexible
than the conventional reinforced concrete wall; therefore, it can withstand
larger foundation settlement. The facing panel rests directly on the ground
(or on a narrow footing if the ground is "weak"). Movement of facing panel
can occur at its base if the lateral thrust exceeds the frictional resistance at
the base. The "deformable" connection between the anchor and facing panel
also allows movement of the facing panel when the lateral thrust becomes
"excessive." The final position of the facing panel can be adjusted to achieve
proper alignment.
The IFF wall is low in total cost. The total cost of the MSB wall may be as
low as 1/3 or even 1/2 of that of a comparable cantilever reinforced concrete
retaining wall.
The IFF wall can potentially accommodate large settlement of highly
compressible backfill without causing distress in the facing panel.
The construction method has been tested with full-scale loading tests
conducted at the University of Colorado at Denver (Wu, et al., 1993). The tests
indicated that the reinforced soil mass exerted very small lateral earth pressure on
the full-height facing panel and that the alignment of the panel can indeed be
adjusted after construction.
6


1.4 Contents of the Report
This report describes the project in Chapter 2. Chapter 3 describes the
instruments used, the instrumentation program, and reduction of the measured
data. Chapter 4 presents the measurement data, by way of figures and tables and
discusses the measured performance of the wall. Whenever applicable,
comparisons of the measured values with the design values were made, and
design implications were addressed. A summary and conclusions of the study is
presented in Chapter 5.
7


2. Project Description
2.1 The IFF Reinforced Soil Retaining Wall
The wall height varied from 5.7ft at the north end to 18.8ft at the south
end. The total wall length was over 1,400ft. Mr. Mike McMullen of the CDOT,
who was the major inventor of the IFF wall, designed the retaining wall. A
typical cross section of the retaining wall is depicted in Figure 2.1. As described
in Chapter 1, the wall system has three major components: full-height reinforced
concrete facing panels, reinforced soil mass (i.e., backfill reinforced with layers of
reinforcement), and face anchors (attaching facing panel to the reinforced soil
mass). For this project, the facing panels were 4fit- or 8flt-wide reinforced
concrete panels. The reinforcement used was a welded wire mesh, 8ft by 20 ft in
size. The wire was 3/16-in. diameter epoxy-coated steel. The grid size of the
mesh was 1ft by 1ft. The face anchors were #5 epoxy-coated rebars, shaped as
one half of a 12-sided symmetric polygon. The rebars were attached to the facing
panels (with threaded screws and nuts) in the gaps between adjacent facing
panels. The nuts can be backed off to adjust the alignment of the facing panels
during and after construction. The completed structure is shown in Figure 2.2.
8


Figure 2.1 Typical Cross Section of the Retaining Wall
9


Figure 2.2 Completed IFF MSB Wall.


2.2 Construction Method
Construction of the retaining wall can be described in the following steps:
1. Excavate a trench at the planned location of facing panel. The trench
should be at least 2ft in depth.
2. Position facing panel in the trench with a required setback, and use flow
fill (a mixture of concrete sand, cement and water in a flowable
consistency) and temporary bracing (in front of facing panel) to brace the
panel in position in the trench (see Figure 2.3).
3. Place backfill behind wall facing, compact the fill to the specified density,
and lay reinforcement at every prescribed interval (i.e., prescribed vertical
spacing).
4. Install the face anchors (rebars) at selected elevations, and continue the
placement of reinforced fill until the design height is reached.
It is to be noted that the vertical spacing of the reinforcement prescribed in
this project was 1.0ft. The mesh was laid tightly against the back of the facing
panels. In the lower levels, the mesh was laid long-end (i.e., the 20-ft side)
against the panels and in the upper levels the mesh was laid short-end (i.e., the 8-
ft side) to the wall (see Section 3.2 for details). The rebar face anchors were
installed at H = 0 (ground surface), 6ft, and lift above the ground surface for
Station 3116, and H = 0 (ground surface), 3ft, and 7ft above the ground surface
11




for Station 3119. The setback used in the construction was determined as a
function of wall height. Typical setbacks used in the project were as follows:
Table 2.1 Typical Setbacks
1 Panel Height 6ft 12 ft 14 ft 23 ft
Top Setback : 0.96 in. 2.16 in. 2.4 in. 4.8 in.
2.3 Fill History
Construction of the project began in early June 1996 and was completed in
August 1996. The traffic along Interstate-25 was kept open without disruption
during entire construction operation. The fill history charts, as deduced from the
field log, for Stations 3116 and 3119 are shown in Figures 2.4 and 2.5,
respectively.
13


Figure 2.4 Fill History of Station 3116


10
9
8
7
6
5
4
3
2
1
0
Date
Figure 2.5 Fill History of Station 3119


3. Instrumentation
3.1 The Instruments
A number of instruments were employed to monitor the performance of
the retaining wall during and after construction. The instruments and their
applications were:
Total station and survey targets: The survey targets were mounted on the
surface of selected facing panels in the test sections. The total station was
used to measure the distances and elevations at the targets.
Vibrating wire inclinometers: These were Geokon Model 6300 vibrating
wire in-place inclinometers. Two inclinometers were affixed to the back
center of 8ft-wide facing panels, one at the top and the other at the bottom,
to monitor movement of the facing panels.
Vibrating wire rebar strain meters: These were Geokon Model 4911A
rebar strain meters. The strain meters were installed at the two ends of the
face anchors where the anchors were attached to the facing panels to
measure strains. These strains can be used to determine the forces exerted
by the reinforced fill on the facing panels.
Vibrating wire strain gages: These were Geokon VK4100 strain gages
mounted at selected points on the welded wire mesh reinforcement to
measure strains in the welded wire mesh.
16


Thermistors: Thermistors were installed adjacent to the strain gages to
monitor the temperatures at the time gage readings were taken.
A total of 48 survey targets (24 on each Station), 2 inclinometers, 32 wire
mesh strain gages, 21 rebar strain meters, and 16 themistors were employed.
Some of the strain gages were malfunctioned before or during construction.
3.2 Layout of Instruments
The layout of the instruments used in this project is shown in Figures 3.1
to 3.6. The layouts of the face anchor strain meters and the inclinometers are
depicted in Figures 3.1 and 3.2 for Stations 3116 and 3119, respectively. The
layouts of the wire mesh strain gages for Stations 3116 and 3119 are depicted in
Figures 3.3 and 3.4, respectively. Note that the elevations at which face anchors
were installed are also marked in the Figures. Figures 3.5 and 3.6 depict the
layouts of the wire mesh strain gages at different elevations (with corresponding
elevations shown in Figures 3.3 and 3.4) for Stations 3116 and 3119, respectively.
All the sensor gages were labeled corresponding to a specific location
within the reinforced soil mass as seen in Figures 3.1 to 3.4. Labels with a 5-digit
number are for the rebar strain meters, while labels with 2 digits correspond to
inclinometer sensors. Wire mesh strain gages have two letters and one digit in
their labels. The three-character labeling of wire mesh strain gages for station
3116 bears the following meaning:
17


19 20 21
22 23
24 25 26
H= lift
H = 6 ft
H = Oft
#71
10300 TT 9 M.
1 \o30i ( 10303 10316 10310 10314 1
/ ;' Two? 10313 1 11
1 1 1 n 11
Un-gag< ;d Rebar Inclinometer #70 / / / 1 \ Gaged l Rebar
Location of Perpendicular
Mesh Gage Alignment
Figure 3.1 Layout of Face Anchor Strain Meters and Inclinometers for Station 3116


56 57 58
59
60
61 62 63
# 68
10311
H = 7 ft ^ H = 3 ft ^10317 l 10312 >,10304 r 10298
H = 0 ft - 10306 ^10302 10299 s 10318 10308
so A
U #69
Gaged Rebar
A
Location of Perpendicular
Mesh Gage Alignment
A
Inclinometer
Gaged Rebar
Figure 3.2 Layout of Face Anchor Strain Meters and Inclinometers for Station 3119


Northernost
Northernost
to
o
Strain Gages
Figure 3.3 Layout of Wire Mesh Strain Gages for Station 3116
Northernost


Northermost
Northernost
Q Stj*ofc-i Gages
Figure 3.4 Layout of Wire Mesh Strain Gages for Station 3119


Figure 3.5 Layout of Wire Mesh Strain Gages at Different Elevations for Station 3116


^55555^:
S : Strain Gauge on Mesh
(§): Strain Gauge on each side
of #5 face anchor bar
Figure 3.6 Layout of Wire Mesh Strain Gages at Different Elevations for Station 3119


Table 3.1
Three-Character Labeling for Station 3116 Mesh Strain Gages
1 character: Vf, Sections " ; t <2m character:,. Positions from the wall 3ro character: North or South
1 (@ lowest level) A (closest to the wall) N Northerly
2 (@ 2nd lowest level) B (2nd closest to the wall) S Southerly
3 (@ 2nd highest level) C (3rd closest to the wall)
4 (@ highest Level) D (farthest from the wall)
3.3 Data Reduction
The data acquisition system used in the project has been described by
Blanks (1996). The data reduction for the inclinometers, the rebar strain meters,
and the wire mesh strain gages are described in detail in the Instruction Manuals
for each instrument.
It should be noted that the thermal coefficient of expansion of the steel
vibrating wire is the same as that of the steel wire mesh to which the gage is
attached. As a result, no temperature correction to the measured strains is
required for the wire mesh strain gages.
The following equation for temperature correction needs to be applied to
the strains measured by the rebar strain meters:
^corrected = I(Ri -Ro) x C] + [(T0 -Ti ) x K] ---Equation 3.1
24


where: £ corrected is the temperature-corrected strain
Ro is the initial reading in digits at the time of installation
Ri is the current reading in digits
C is the calibration factor (C = 0.35709 for Model 4911A gages)
To is the initial temperature recorded at the time of installation
Ti is the temperature at the time of reading
K is the thermal coefficient
Note that the coefficient of expansion is 12.2 ppm/C for steel and 11.3
ppm/C for the rebar strain meters. Thus, the thermal coefficient, K, for the rebar
strain meters is 12.2 -11.3 = 0.9 (ppm/C).
Once the strains are obtained, the following equation was used to calculate
the corresponding forces:
F = e E A ------------Equation 3.2
Where: e is the strain
E is the Young's modulus of the material (E is 30 x 106psi for
steel)
A is the cross sectional area (A is 0.31 in.2 for the #5 rebar, and
0.035 in.2 for the wire meshes).
To confirm the EA value used in data reduction, four sets of load-
deformation tests were performed (see Figure 3.7). The average EA value was
found to be 1,013,000 lb. The diameters of the wire mesh at numerous different
25


Figure 3.7 Load-Deformation Testing of Wires Used for Reinforcement
26


locations were measured using a caliper, and an average circular cross sectional
area was determined to be 0.03509 in2. Using Equation 3.2, the value of E was
calculated as 28.9 x 106psi, which is fairly close to the typical value of 30 x
106psi.
27


4. Measured Results and Discussion of Results
4.1 Measured Data in Excel
The measured data, including the survey data, the inclinometer data, the
wire mesh strain data, and the rebar strain data (with corresponding temperature
readings) were organized using a computer-based spreadsheet program, Excel.
4.2 Wall Movement
The movement of the wall (i.e., the facing panels) during and after
construction was measured by a precision surveying method and by
inclinometers. It should be noted that the dates appear in this report that are
without specification to the year are for the year 1996.
4.2.1 Surveying
Figure 4.1 shows the cumulative change in elevation at H = 1ft, 4ft, and
7ft for Station 3116. The reference for these survey data was the survey reading
on June 18 when the first set of survey data was taken; at which time the fill
height was 5ft above ground. It is seen that there are significant variations with
the survey data at different targets/panels. However, when average values are
taken, as shown in Figure 4.2, the displacement curves follow a fairly consistent
downward trend. The change in elevation from June 18 to June 26 (full fill
28


NJ
VO
DATE
Figure 4.1 (a) Cumulative Change in Elevation vs. Time for Station 3116 at H=lft


U1
o
*2
-6-8
-*-11
-*-14
-17
i20
DATE
Figure 4.1 (b) Cumulative Change in Elevation vs. Time for Station 3116 at H=4ft


0.00
-0.08 -I--------------1-------------1--------------1--------------1--------------1--------------1-------------^
00 C4 on o m o JO
IT C! m 00
O VO r- r-
DATE
Figure 4.1 (c) Cumulative Change in Elevation vs. Time for Station 3116 at H=7ft


TIVE CHANGE IN ELEV. (ft)
uj
s>
H=7ft
-*-H=4ft
*-H=lft
Figure 4.2 Average Cumulative Change in Elevation vs. Time for Station 3116


height) was 0.024ft (0.29in.). From June 26 to August 5, an additional settlement
of 0.028ft (0.34in.) occurred. There was a slight "rebound" past August 5. The
downward movement was primarily due to settlement of the foundation soil.
Figure 4.3 shows the cumulative change in distance at H = 1ft, 4ft, and 7ft
for Station 3116. The data also have significant variations as in Figure 4.1. The
average cumulative change in distance is shown in Figure 4.4. The survey
equipment was placed across Interstate-25 in the parking lot of Regency Hotel.
These data have the same reference as those of Figure 4.1. The negative values
indicate that the panel moved outward (i.e., toward Interstate-25). As expected,
the outward movement was larger at the top of the panels and smaller near the
bottom. From June 18 (fill height = 5ft) to June 26 (full fill height), the wall
moved out 0.155ft (1.85in.) at H = 7ft. After June 26, the outward movement of
the panels was relatively small. The outward movement at H=7 ft measured on
August 9 (with fill height of 5ft as reference) was 0.21ft (2.5in.). The "top"
setback of 2.4 in. for 14-ft high panels (see Section 2.2) appears to be a little too
small. Based on the survey measurements, the top setback for 14-ft high panels
should be at least 3.7 in.
Figure 4.5 shows the cumulative change in elevation at H = 1ft, 4ft, and
7ft for Station 3119. The reference for these survey data was the reading taken
on July 1, 1996; at which time the fill had not begun. It is seen that there are
also significant variations with the survey data at different targets/panels. When
33



-*-12
-*-15
18
i 21
---24
Date
Figure 4.3 (a) Cumulative Change in Distance vs. Time for Station 3116 at H=lft


0.00
-0.20 +-
oo
vO
-H
vO
00
Figure
4.3 (b) Cumulative Change in Distance vs.
Time for Station 3116 at H-4ft


0.00
u>
On
-0.05 -
£ -0.10 -
4)
be
c

5 -0.15
9
E
9
u
-0.20 -
-0.25 +
00
NO
5

ON
NO
pH

o
fO
-+-
iO
00
Date
Figure 4.3 (c) Cumulative Change in Distance vs. Time for Station 3116 at H=7ft


Figure 4.4 Average Cumulative Change in Distance vs. Time for Station 3116
Li
CUMULATIVE CHANGE IN DIST. (ft)
1 o SJ N> I o
o O


(j)
00
Date
Figure 4.5 (a) Cumulative Change in Elevation vs. Time for Station 3119 at H=lft


0.02
UJ
so
0.00
-0.02
Im

_4)
w

at
0
a
JS
O
-0.04
-0.06
-0.08
-0.10
-0.12
a 8
-*-11
14
17
-*-20
---23
-0.14 ----------------1----------------1---------------1----------------1---------------1----------------
7/1 7/15 7/19 7/26 8/1 8/12 8/16
Date
Figure 4.5 (b) Cumulative Change in Elevation vs. Time for Station 3119 at H=4ft


Cumulative Change in Elev. (ft)
0.02
-O.
o
0.00
-0.02
-0.04
-0.06
-0.08
-0.10 --
-*-10
-*-13
-*-16
-*-19
---22
-0.12
VO VO VO o
r5 00 9 1 00
-+
U1
00
Date
Figure 4.5 (c) Cumulative Change in Elevation vs. Time for Station 3119 at H=7ft


average values are taken, as shown in Figure 4.6, the displacement curves again
follow a fairly consistent trend. The change in elevation from July 15 (fill height
= 4ft) to July 26 (fill height = 9ft) was about 0.05ft (0.6in.). As in Station 3116,
the facing panels continued to move downward after full fill height was reached.
The loading history beyond July 26 was not available.
Figure 4.7 shows the cumulative change in distance at H = 1ft, 4ft, and 7ft
for Station 3119. The average cumulative change in distance is shown in Figure
4.8. The survey equipment was also placed in the parking lot of Regency Hotel.
As in Station 3116, the outward movement was larger at the top of the panels and
smaller near the bottom. The change in distance from July 1 to July 26 (fill height
= 9ft) at H = 7flt was 0.17ft (2.0in.). After the full fill height was reached (i.e.,
after July 26), the outward movement was very small. It appears again that the
top setback of 2.16in.for 12-ft high panels (see Section 2.2) may be a little too
small. Based on the survey measurements, the top setback for 12-ft high panels
should be at least 2.6 in.
4.2.2 Inclinometer
The histories of wall deflection rate (space rates), as deduced from
inclinometers for Stations 3116 and 3119, are shown in Figures 4.9 and 4.10. The
figures are plotted using the data reduced by CDOT personnel. It should be
noted that since the facing panels on which the inclinometers were affixed were
41


fe.
K)
H=7ft
*11=46
H=lft
Date
Figure 4.6 Average Cumulative Change in Elevation vs. Time for Station 3119


u>
Figure 4.7 (a) Cumulative Change in Distance vs. Time for Station 3119 at H=lft


-fc.
*2
a8
-**-11
-*-14
17
t20
---23
Figure 4.7 (b) Cumulative Change in Distance vs. Time for Station 3119 at H=4ft



Figure 4.7 (c) Cumulative Change in Distance vs. Time for Station 3119 at H=7ft


*>
Ov
H=7 ft
H=4 ft
Figure 4.8 Average Cumulative Change in Distance vs. Time for Station 3119


Figure 4.9 Wall Deflection Rate vs. Time for Station 3116
Deflection Rate (in./ft wall height)
o o o o o
O O O
O 4k 00 to 0\
OZ'O


Deflection Rate (in./ft wall height)
DATE
Figure 4.10 Wall Deflection Rate vs. Time for Station 3119


moving in both lateral and vertical directions during construction (as evidenced
by the survey data), the actual deflections of the facing panels cannot be obtained
from the measured data of the inclinometers. The inclinometer data, however,
can be used to determine the angles of rotation of the facing panels. These data
can be used to estimate the relative outward movement between two selected
points on the panels.
For Station 3116, the survey results (see Figure 4.4) showed that the
difference in outward movement between H = lift and H = 7ft was 0.15ft 0.08ft
= 0.07ft (0.84in.) on June 26, 1996 (with full fill height). From Figure 4.9, the
deflection rate per foot of wall height was 0.12in. on June 26. The relative
outward movement over the 6-ft interval (from H = 1 ft to H = 7ft) is, therefore,
012 in./ft 6ft = 0.72in. The agreement between the results obtained from the
survey and the inclinometers is quite good. It is noted that the Figure 4.9 shows
that the deflection rate continued to increase beyond June 26. The survey results
(Figure 4.4) also indicate the same trend.
For Station 3119, the survey results (see Figure 4.8) showed that the
difference in outward movement between H =1 ft and H = 7ft was 0.17ft 0.07ft =
0.10ft (1.2in.) on July 26, 1996 (near full fill height). Figure 4.10 shows that, on
July 26, the deflection rate per foot of wall height is 0.09in. The relative outward
movement over the 6-ft interval (from H = 1 ft to H = 7ft) is, therefore, 0.09 in./ft
* 6ft = 0.54in. The agreement between the results obtained from the survey and
49


the inclinometers in this case is not as good as in Station 3116. The values,
however, are on the same order of magnitude. It is noted that Figure 4.10
indicates that the deflection rate was almost constant soon after July 26. The
survey results (Figure 4.8) also show the same trend.
It can be concluded that the inclinometer results are consistent with those
obtained from the precision survey method.
4.3 Forces in Wire Mesh Reinforcements
The measured wire mesh strains at H = 1ft, 4ft, 7ft, and lift as a function
of time for Station 3116 are shown in Figure 4.11. It is seen that some of the
measured strains (e.g., Gages 1-C-S, 2-A-N, 4-B-N, and 4-D-S) fluctuated
severely and many readings went out of the range of the plots. Most of the
fluctuations occurred after the full fill height had been reached. The fluctuated
strain data were eliminated before conducting further analysis. Figure 4.12 shows
the measured wire mesh strains at H = 1ft, 3ft and 5ft for Station 3119. The strain
gage at H = 5ft had significant fluctuation. The strains at H = 1ft and 3ft were
mostly compressive. It should be noted that all the strains were determined by
subtracting the initial strain from the subsequently measured strains. The initial
strain corresponds to some unknown load level of the wire mesh before
installation. In some cases, the initial strain fluctuated significantly. Judgements
were made to select a "stable" strain taken a few days after the initial reading as
50


Micro Strain

1-A-S
-a- 1-B-N
-A-l-C-S
Date
Figure 4.11(a) Strains in Wire Mesh vs. Time for Station 3116 at H = 1ft


Micro Strain
2000
ro
1500 -
1000 -
500 -
0 -
-500 -
*
2-A-S
H 2-A-N
A 2-B-S
X 2-B-N
X2-C-S
2-C-N
-1000
O'
r<
vS
t--------------i--------------1-------------1-------------1--------------1-------------1--------------1-------------1-------------1--------------r
04 t" 04 o^ cs O' 04 t- VO ii vO
04 04 04 04 00 00
v5 VO O' S ft 00 00
Date
Figure 4.11(b) Strains in Wire Mesh vs. Time for Station 3116 at H = 4ft


Micro Strain
2000
iy>
u
1500 -
-500 -
1 (S 1 r- 1 Cl 1 1 jm JN CM CM 00 00
VO VO r-* r f" 00 00
Date
Figure 4.11(c) Strains in Wire Mesh vs. Time for Station 3116 at H = 7ft


Micro Strain
2000
4*.
1500 -
1000 -
500 -
0 -
-500 -
4-A-S
O4-A-N
it 4-B-S
K 4-B-N
*f 4-C-S
4-C-N
4-D-S
----4-D-N
IUUU i i 1 " 1 "f - l 1 1 1 . .
cs CN cs
VO VO 00 00 00 00
Date
Figure 4.11(d) Strains in Wire Mesh vs. Time for Station 3116atH=llft


, Micro Strain

Date
H=lft
0H=3ft
AH=5ft
Figure 4.12 Strains in Wire Mesh vs. Time for Station 3119 at H = 1 ft, 3ft and 5ft


the initial strain.
Figures 4.13 shows the forces in the wire mesh at H = 1ft, 4ft, 7ft, and 11ft
of Station 3116. It is seen that, although the wall was approximately in a state of
plane strain condition, most of the forces varied widely in the longitudinal
direction of the wall. For example, the forces at Gage 2-B-N were more than
eight times the forces at Gage 2-B-S (see Figure 4.13 (b)). These forces should
have been very similar because the two gages were located at the same distance (x
= 3.5ft) from the wall face.
The only pair of "stable" curves at H = 7ft were obtained from Gages 3-B-
S and 3-B-N (see Figure 4.13(c)). The forces at Gage 3-B-S were more than
twice the forces at Gage 3-B-N, although they are expected to be very similar in
magnitude. The other data fluctuated up and down and were considered
unreliable.
For the gages at H = lift, the only pair of "stable" curves of Figure
4.13(d) were obtained from Gages 4-A-S and 4-A-N, both located at x = 1.5ft.
Not only the magnitude of the two gages was vastly different, one curve showed
compressive force, the other tensile forces. The other data were considered
unreliable.
It was disappointing that most of the data for the wire mesh reinforcement
were judged to be unreliable. It should be noted, however, that the data could be
manipulated to show better correlation with one another. This will require the use
56


Force (kips)
VI
Date
Figure 4.13(a) Forces in Wire Mesh vs. Time for Station 3116 at H = 1ft


SA
8S
Force (kips)
p
oo
o
On
O
O
K>
O
o
o
K)
o
fc.
o
On
O
00
3
tf
o
3
o
CO
M
9
3
S'
s
<0
co
9*
H
B
0
01
n
Cfl

5
9
On
W
-U
3>


Force (kips)
ISI
Date
3-A-N
H3-B-S
A3-B-N
-K-3-C-N
Figure 4.13(c) Forces in Wire Mesh vs. Time for Station 3116 at H = 7ft


Force (kips)
1.0
Ov
o
0.8 -
0.6 -
0.4 -
0.2 -
0.0 -
-0.2 -
-0.4 -
-0.6 -
*-4-A-S
H 4-A-N
A 4-B-S
X 4-B-N
X4-C-S |
4-C-Nj
I 4-D-S i
I
----4-D-N!
-0.8 -
1 CN 1 r- 1 CN i r- 1 CN l 1 CN ( 1 VO VO
CN CJ CN 00 00
VO \£> t- r" r- 00 00
Date
Figure 4.13(d) Forces in Wire Mesh vs. Time for Station 3116 at H = 11ft


of artificial values for the initial strains. It was deemed inappropriate to do so, as
the conclusions reached would be subject to a high degree of uncertainty.
Figure 4.14 shows the forces in the wire mesh at H = 1ft, 3ft, and 5ft of
Station 3119. It is seen that the forces at H = 1ft and 3ft are mostly compressive.
At H = 5ft, the forces increased steadily and significantly from July 18 to July 28
(near full fill height) and only increased slightly after July 28. The magnitude of
the forces was much larger at H = 5ft than at H = 1ft and 3ft. The minimum yield
force of the 3/16 in. diameter wire mesh is cry *A = 65 [it* (3/32)2] = 1.8 (kips),
and can go as high as 2.8 kips. It is seen that the forces in the wire meshes at H =
5ft either reached or approached the yield state around July 24 (refer to Figure 2.5
for fill history), had the yield stress been 65kips/in2. It should be noted that when
the yield state is reached, the force will remain essentially constant (until the
strain exceeds approximately 10 times the yield strain), as shown in the dashed
line in Figure 4.14.
Figures 4.15 shows the distribution of wire mesh forces with the distance
from the Station 3116 wall face at H = 1ft, 4fit, 7ft, and 11 ft on July 1 and August
1, 1996. This figure was prepared by assuming the measured forces were
reasonably correct. When the difference of two readings at the same distance
from the wall face was within 50%, an average value of the two was used.
Otherwise, the data judged to be more reasonable were employed. Note that
full fill height was nearly reached on June 26. Two days later, 3ft-thick of soil
61


Force (kips)
2.6 -
o\
K>
2.1 -
1.6 -
1.1
0.6 -
R-1-GAG
0.1 -
-0.4 4-
00
CN
-I----------1----------1----------r
vo o co
CJ CJ oo oo
t> o
Date
t---------------------r
'H IT)

00 00
Figure 4.14(a) Forces in Wire Mesh vs. Time for Station 3119 at H = 1 ft


Force (kips)
CT\
u>
Date
R-2-GAG
Figure 4.14(b) Forces in Wire Mesh vs. Time for Station 3119 at H = 3 ft


Force (kips)
CT\
-P-
+R-3-GAG
Date
Figure 4.14(c) Forces in Wire Mesh vs. Time for Station 3119 at H = 5ft


Force (kips)
a 7/1/96
8/1/96
Figure 4.15(a) Forces along the Length of Wire Mesh for Station 3116 at H = lft


Force (kips)
X(ft)
-a7/1/96
8/1/96
Figure 4.15(b) Forces along the Length of Wire Mesh for Station 3116 at H 4ft


Force (kips)
a 7/1/96
8/1/96
Figure 4.15(c) Forces along the Length of Wire Mesh for Station 3116 at H = 7ft


Force (kips)
X(ft)
Figure 4.15(d) Forces along the Length of Wire Mesh for Station 3116atH=llft


surcharge was placed. The data on July 1 were plotted because its data were more
complete than other dates around the time of full fill height. The reason for
selecting August 1 was because the forces on that day were typical maximum
forces and the data were fairly complete. Also note that the wire meshes at H =
lft and 4ft were of shorter reinforcement length, and the wire meshes at H = 7ft
and 1 lft were of longer reinforcement length (see Figure 2.6).
It is seen, from Figure 4.15 that from July 1 till August 1, the magnitude of
the forces changed only slightly. The larger change occurred at H = 7ft and 1 lft.
This is not unexpected since the wall movement, after the full fill height had
reached, occurred mostly in the upper portion of the wall. At H = 1 lft, the forces
increased by about 0.4 kips over the one-month period.
The major reason for plotting Figure 4.15 was that it should reveal the
locus of the potential failure surface (by connecting points of the maximum force
in each reinforcement layer) if the ultimate failure mode were to be rupture of the
reinforcement. The maximum forces in different layers of reinforcement shown
in Figure 4.15, however, did not resemble any smooth curves. This is primarily
because the measured values of the forces are not reliable. The attempt to make
the best of the data was not successful in this case.
It is important to point out that the maximum force in the reinforcements
of Station 3116 was at Gage 1-B-N, located at H = lft and x = 3.5ft (see Figure
4.13(a)). The largest force was 0.61 kips, occurred from August 6 to August 16
69


(when the measurement was terminated). This force was below the minimum
yield force of 1.8 kips.
Under Ko- and Ka-conditions, the lateral thrusts are, respectively, K0yz and
Kayz. At H = 1ft, z is equal to 15.25ft 1ft = 14.25ft. Therefore, K<,yz =
0.441(0.125)(14.25) = 0.79 kips/ft, and Kayz = 0.283(0.125)(14.25) = 0.50 kips/ft,
assuming <|> = 34, and y = 125 pcf. The measured value of 0.61 kips (or 0.61
kips/ft since the vertical spacing of the reinforcement was 1ft and the grid size of
the mesh was 1ft by 1ft) at Gage 1-B-N was between the values at K0- and In-
states.
It should be noted that although the measurements of Gage 1-C-S (also at
H = lft) had severe fluctuation, there was a maximum value of 0.74 kips. The
implication in design is that, if = 34 is assumed for the backfill, it may be
prudent to assume Ko-condition when evaluating the required strength of
reinforcement.
4.4 Forces on Facing Panels
The forces on the facing panel were obtained from the forces in the rebars
installed between adjacent facing panels. The forces in the rebars were
determined from strains in the rebars, measured by strain gages. The measured
strains were corrected for temperatures using Equation 3.1 before the forces were
70


calculated. As with other measurements, rebar data that show drastic and sudden
change were eliminated from the analysis.
The measured strains in the rebars for Stations 3116 were collected
manually by a Geokon portable device prior to July 1, 1996 and recorded
automatically by CR-10 automatic data acquisition system after July 13. The
measured raw data before July 1 were on the order of +6000 micro-strain. Those
measured after July 13 were on the order of -2000 micro-strain.
Figure 4.16 shows the rebar forces at H = 0, 6ft and 11ft for Station 3116.
In plotting the Figure, it was tacitly assumed that the forces measured on July 13
by the CR-10 were identical with those measured on July 1 by the portable
device. However, since the forces were dropping between June 28 and July 1 (as
measured by the portable device) in all the gages, this assumption may be
questionable.
Figure 4-16 indicates that the forces measured in different panels at a
given height did not vary significantly, and they do not vary significantly with
time after July 13, 1996. Before July 1, 1996, the measured forces at H = 0 and H
= 11 ft fluctuated to some degrees, thus their values are considered not very
reliable. The measured forces at H = 6ft were fairly consistent.
According to the measurements, the largest rebar forces occurred at H = 6
ft, and the forces were smallest at H = 0. The largest forces occurred on June 27
or June 28, around the time when the full fill height was reached. The ranges of
71


Force (kips)
4.5
-j
K>
4.0 -
3.5 -
3.0 -
2.5 -
2.0 -
1.5 -
1.0 -
0.5 -
0.0 \m\
-0.5
6/17
6/27
10314
10307
-Ik- 10313
111 im mi 8/6 8/16
Date
Figure 4.16(a) Forces in Rebar vs. Time for Station 3116 at H = Oft


Force (kips)

-10310
--10303
A10305
Figure 4.16(b) Forces in Rebar vs. Time for Station 3116 at H = 6ft


Force (kips)
4.5

4.0 -
3.5 -
3.0 -
2.5 -
2.0 -
1.5 -
1.0 -
0.5 -
0.0 -
-0.5
6/17

-10316
10300
-A-10301
i---------------1---------------1--------------1--------------1--------------1-1
6/27 7/7 7/17 7/27 8/6 8/16
Date
Figure 4.16(c) Forces in Rebar vs. Time for Station 3116 at H 11 ft


the maximum rebar forces in different panels were:
Table 4.1
Average Rebar Forces at Different Heights for Station 3116
Height 0 (ground surface) 6ft lift
Maximum Force* 0.16 to 0.61 kips 3.27 to 4.16 kips 1.37 to 2.40 kips
* assuming the forces af ;er July 13 were not larger than the maximum values
For Station 3119, the data were also recorded initially by the portable
Geokon device and later switched to the CR-10. Since there was only one set of
data recorded by the portable device, the initial reading was not obtainable. Only
the change in forces after July 14, 1996 can be evaluated. Figure 4.17 shows the
change in rebar forces, after July 14, at H = 0, 3ft and 7ft for Station 3119. It is
seen that the forces in the gages at H = 0 and 3ft vary significantly around July 16
when 4 ft of fill was added. The average forces at the three heights are plotted in
Figure 4.18. The largest change in the (average) rebar forces at different heights
till July 26,1996 (fill height = 9ft) and over the entire monitoring period were:
75


Force (kips)
10308
10318
A10306
Figure 4.17(a) Forces in Rebar vs. Time for Station 3119 at H = Oft


Force (kips)

10298
-H-10304
A10299
-X- 10302
Figure 4.17(b) Forces in Rebar vs. Time for Station 3119 at H = 3ft


Force (kips)
oo
2.0 -r
1.5 -
1.0 -
0.5 -
0.0 -
-0.5 -
-1.0 -
-1.5 -
-2.0---------------1-------------1------------1-------------1------------1-------------1
7/15 7/20 7/25 7/30 8/4 8/9 8/14
Date
10317
-a-10312
A10311
Figure 4.17(c) Forces in Rebar vs. Time for Station 3119 at H = 7ft


Force (kips)
*-H=0ft
HH=3ft
AH=7ft
Figure 4.18 Average Forces in Rebar vs. Time for Station 3119


Table 4.2
Average Rebar Forces at Different Heights for Station 3119
1 Height 0 (ground surface) 3ft 7ft
1 Largest increase* in Rebar Force till July 26* -0.65 kips -1.01 kips -0.38 kips
Largest increase;* in Rebar Force over entire period -0.76 kips -1.19 kips -0.87 kips
* increase since July 14,1996
The negative sign in the above Table indicates that there was either a
reduction in tensile force or an increase in compressive force. It is possible that
this is correct due to the temporary bracing used during construction (see Section
2.2) and the fact that the bottom portion of the panel was embedded and supported
by a flow fill. However, it appears to be contradictory to the movement of the
facing panels as described in Section 4.2.1. There was likely an error in the
positive/negative sign of the recorded values. In any case, since the forces prior
to July 14 were not known for Station 3119, this issue becomes inconsequential.
The measured data, however, do indicate that the increase in the rebar forces was
fairly small. Upon increasing the fill height from 4ft to 9 ft, the rebar force
increased by a total maximum of 2.04 kips. The total maximum increase in rebar
force was 2.82 kips after July 14, 1996.
The lateral thrust, under Ko-condition, for a 15.25 ft high wall over an 8-fit
wide panel is V* K<,yH2(w) = (1 sin 34)(0.125)(15.25)2 (8) = 51.2 (kips), with
80


the assumption that = 34 and y = 125 psf. Under Ka-condition, the lateral thrust
will be 32.8 kips. These forces are much greater than the sum of the maximum
rebar forces (7.2 kips) for station 3116. Also, the increase in lateral thrust for fill
height increasing from 4 ft to 9 ft is 14.3 (kips) under Ko-condition, and 9.2 kips
under Ka-condition. These forces are, again, much greater than the sum of all the
maximum increase in rebar forces (2.0 kips) for Station 3119. Clearly, the
assumption of either Ko- or Ka-condition for determining the lateral thrust acting
on the wall would have resulted in a drastic over-estimation.
The fact that the lateral earth pressure is very small has been demonstrated
in a number of full-scale controlled tests conducted at the University of Colorado
at Denver (Helwany, 1994). Figure 4.19 shows a photograph taken during one of
the full-scale tests. With the surcharge being applied, the concrete facing panel
was removed. It is seen that the reinforced soil mass remained stable (the surface
was stained to observe if there would be any falling soil particles) for a long
period of time.
81


Figure 4.19 Surface of Reinforced Fill in Full-Scale Test
after Removal of Facing Panel
82


5. Summary and Conclusions
5.1 Summary
In 1996 the Colorado Department of Transportation (CDOT) constructed a
new retaining wall for the ramp connecting Northbound Interstate-25 to Interstate-
70. A new construction technique that uses an Independent Full-height Facing
(IFF) panel in front of a reinforced soil mass was adopted. The new construction
technique was adopted because it does not require over-excavation in front of the
wall. This feature allows the traffic to remain open throughout the construction
and alleviate the need to deal with excavation and disposal of contaminated
subsoil.
The IFF wall system has three major components: full-height reinforced
concrete panels (as the wall facing), reinforced soil mass (comprises the backfill
and layers of reinforcement), and face anchors (to attach facing panel to the
reinforced soil mass). For this project, the facing panels were 4ft- or 8ft-wide
reinforced concrete panels. The reinforcement used was 3/16-in. diameter epoxy-
coated steel welded wire mesh. The face anchors were #5 epoxy-coated rebars,
shaped as one half of a 12-sided symmetric polygon. The two ends of the face
anchors were attached to the wall face in the gaps between adjacent facing panels.
Two sections of the retaining wall were instrumented to monitor the
performance during and after construction. These sections were designated as
83


Station 3116 and Station 3119. The instruments employed (with their respective
functions in parenthesis) were:
survey total station and survey targets (to measure movement of facing
panels)
vibrating wire inclinometers (to measure rotation of facing panels)
vibrating wire rebar strain meters (to measure forces in face anchors at
wall face)
vibrating wire strain gages (to measure forces in wire mesh
reinforcement)
thermisters (to monitor temperatures near strain gages).
A total of 48 survey targets (24 for each Station), 2 inclinometers, 32 wire mesh
strain gages, 21 rebar strain meters, and 16 themistors were employed. Some of
the strain gages were malfunctioned before or during construction.
This study was undertaken to organize the measured data and to
synthesize the measured data and assess the design assumptions. Since a number
of persons were involved in different stages of the project and some are no longer
with CDOT, proper organization and interpretation of the measured data became a
rather challenging task. Judicious judgements had to be made in the interpretation
of the data as some of the measured data were not entirely stable. Whenever
applicable, the measured data were compared with the design values to evaluate
the design assumptions.
84


5.2 Findings and Conclusions
The findings and conclusions of this study, including those on wall
movement, forces in the wire mesh reinforcements, and forces on the facing
panels, are summarized as follows:
1. The survey data indicated that, from June 18 (fill height = 5ft) to June 26
(full fill height), the downward movement of the facing in Station 3116
was 0.29in. From June 26 to August 5, an additional settlement of 0.34in.
occurred. The downward movement was primarily due to settlement of
the foundation soil. For Station 3119, the downward movement was 0.6in.
from July 15 (fill height = 4ft) to July 26 (fill height = 9ft).
2. For Station 3116, the outward movement of the facing panel at H = 7ft
was 2.5in. from June 18 (fill height = 5ft) till August 9 (almost 1 XA moths
after reaching full fill height). The initial "top" setback of 2.4in. for 14ft-
high panels, therefore, was a little too small. Based on the survey data, the
top setback for 14-ft high panels should be at least 3.7in.
3. For Station 3119, the outward movement of the facing panel at H=7ft was
2.0in. from July 1 (fill height = 0) to July 26 (fill height = 9ft). The initial
"top" setback of 2.16in. for 12ft-high panels, therefore, was also a little too
small. Based on the survey data, the top setback for 12ft-high panels
should be at least 2.6in.
85


4. The inclinometers were affixed to the back of the facing panels. Since the
panels moved in both lateral and vertical directions (as evidenced by the
survey measurement), the actual deflection of the facing panel cannot be
measured by the inclinometers. For Station 3116, the difference in
outward movement between H = 1ft and H = 7ft at full fill height was
0.84in. Compared with 0.72in. obtained from the survey data, the
agreement between measurements from the survey and the inclinometers
was very good. For Station 3119, the relative outward movement was
1.2in. Compared with 0.54 in. from the survey data, the agreement was
not as good as in Station 3116. The values, however, are on the same
order of magnitude.
5. Some of the measured strains in the wire mesh reinforcements fluctuated
severely. After eliminating those apparently bad data from the analysis,
most of the calculated forces still varied widely in the longitudinal
direction of the wall. For example, the forces at Gage 2-B-N were more
than eight times the forces at Gage 2-B-S, despite the two gages were
located at the same distance (x = 3.5ft) from the wall face. It should be
noted that the data could have been manipulated to obtain a better
correlation with one another. This will require the use of artificial values
for the initial strains. It was deemed inappropriate to do so, as the
conclusions reached would be highly uncertain.
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6. The locus of the potential failure surface can be estimated by connecting
points of maximum forces in different reinforcement layers if the ultimate
failure mode were to be rupture of the reinforcement. The plots of the
distribution of forces at different heights, however, did not yield any
smooth curves through their maximum points. This is primarily because
the measured values of the forces are not reliable. The attempt to make
the best of the data was not successful in this case.
7. For Station 3116, the apparently reliable maximum force in the
reinforcements occurred at Gage 1-B-N, located at H = 1ft and x = 3.5ft.
The maximum force at this location was 0.61 kips, below the yield force
of 1.8 kips. For Station 3119, the forces at H = 1ft and 3ft were mostly
compressive. At H = 5ft, the forces in the wire mesh were approaching
the yielding state as the full fill height was reached.
8. At H = 1ft, the lateral thrust on a 15.25ft-high facing panel is 0.79 kips/ft
under Ko-condition, and 0.50 kips/ft under Ka-condition (assuming 34, and y = 125 pcf). Comparing these analytical values with the
measured values of 0.61 kips at Gage 1-B-N and 0.74 kips at gage 1-C-S
(both at H = 1ft), it may be prudent to assume Ko-condition in design
when evaluating the required strength of reinforcement.
9. The rebar forces (i.e., the forces on the facing panels) for Station 3116
were the largest at H = 6 ft, and smallest at H = 0. The largest forces
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occurred on June 27 or 28, 1996, around the time when the full fill height
was reached. The ranges of the maximum rebar forces were:
Table 5.1
Maximum Rebar Forces at Different Heights for Station 3116
Height 0 (ground surface) 6ft lift
Maximum Force 0.16-0.61 kips 3.27 -4.16 kips 1.37-2.40 kips
The lateral thrust for a 15.25 ft high wall over an 8-ft wide panel is
calculated to be 51.2 kips under Ko-condition, and 32.8 kips under Re-
condition (assuming <|) = 340 and y = 125 psf). These forces are much
greater than the sum of all the maximum rebar forces of 7.2 kips. The
design implication is that the assumption of either Ko- or Ka-condition for
determining the lateral thrust acting on the wall will resulted in a fairly
drastic over-estimation.
10. Due to insufficient data prior to switching the data collection device, only
the change in rebar forces after July 14, 1996 can be evaluated for
Station 3119. Assuming that the recorded strains are of opposite sign, the
largest change in the (average) rebar forces on July 27, 1996 (fill height =
9ft) were:
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Table 5.2
Largest Change in Rebar Forces at Different Heights for Station 3119
Height 0 (ground surface) 3ft 7ft
Largest Increase* | in Rebar Force 0.65 kips 1.01 kips 0.38 kips
* increase since July 14, 1996
The increase in the lateral thrust for fill height increasing from 4 ft to 9 ft
is calculated to be 14.3 (kips) under Ko-condition, and 9.2 kips under Re-
condition. These forces are much greater than the sum of the maximum
increase in rebar forces (2.0 kips) for Station 3119. This confirms the
observation from Station 3116 in that the assumption of either Ko- or Re-
condition would have resulted in a drastic over-estimation of the lateral
thrust acting on the wall.
89