abstract of my thesis
DESCRIPTION
hgTRANSCRIPT
-
vi
3.2.4 Anchorage Elements ................................................................................ 25
3.2.5 Welding Work .......................................................................................... 25
3.3 Soil .................................................................................................................. 26
3.4 Experimental Programs ................................................................................... 27
3.4.1 Compaction Test ...................................................................................... 27
3.4.2 Tensile Tests ............................................................................................ 28
3.4.3 Pull-out Tests ........................................................................................... 30
3.5 Finite Element Analysis .................................................................................. 36
3.6 Conclusion ....................................................................................................... 38
CHAPTER 4 RESULTS AND DISCUSSION ...................................................... 40
4.1 Introduction ..................................................................................................... 40
4.2 Results of Pull-out Test ................................................................................... 42
4.2.1 Pull-out Tests on Plain Strip .................................................................... 43
4.2.2 Pull-out Tests on Strip with 1 cm Anchorage Elements .......................... 46
4.2.3 Summary of Pull-out Tests ...................................................................... 49
4.3 Results of Finite Element Modelling .............................................................. 52
4.3.1 Deformed Mesh ....................................................................................... 55
4.3.2 Axial Force............................................................................................... 57
4.3.3 Zones of Horizontal Displacements ......................................................... 59
4.3.4 Zones of Shear Stresses ........................................................................... 61
4.3.5 Total Principal Stresses ............................................................................ 63
4.3.6 Summary of Finite Element Modelling ................................................... 64
CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS ........................ 66
5.1 Conclusions ..................................................................................................... 66
5.2 Recommendations for Future Works .............................................................. 68
REFERENCES ............................................................................................................. 69
APPENDIX A
APPENDIX B
-
3
1.2 Applications in Malaysia and Abroad
The application method of reinforced soil has been reinvented for design of reinforced
retaining wall (Shukla et al., 2009). In the international arena, the use of reinforced
retaining wall intensified in the 1980s and 1990s (Walls, 2009). In Malaysia, where soil
reinforcement methods have been widely used in geotechnical projects, the use of
reinforced earth for various geotechnical structures has become very popular in recent
years. From the front, view as shown in Figure 1.2 has become common sights in the
country.
Figure 1.2: A View of MRE Showing Decorative Facing
-
8
gave higher increment of stress because sand used in the study consists of poorly
graded and particle size is smaller than red soil and black silty soil.
Figure 2.2: Result of Pull-out Test for Soil-Geotextile Interaction by Awdhesh and
Murali, (2011)
2.4 Boundary Conditions
Sugimoto et al., (2001) concluded that pressure applied on front wall during pull-out
decrease as the position moved from top to bottom with the maximum pressure
occurred near the reinforcement. Farrag et al., (1993) found that the flexible
reinforcement member has better uniform load distribution on interface area. The effect
of the boundary conditions at the front wall has been studied by many researchers using
pressure cells which placed at different position of front wall. Generally these
researchers have found that pressure applied on the front wall increases continuously at
the test progresses (Johnston and Romstad, 1989; Chang et al., 2000).
Palmeira and Milligan (1989a) studied the effect of boundary condition by first
carrying out tests using two types of top boundary rigid and flexible and followed by
different wall roughness coefficient. The results as shown in Figure 2.3(a), the rigid top
Black silty soil-geotextile
Red soil-geotextile
Sand-geotextile
Displacement, mm
Pu
llou
t, k
N/m
-
14
sand thickness encapsulating the geogrid enhanced the reading in pull-out capacity.
Thus, the optimum thickness of sand containing the geogrid was 10mm. Furthermore,
the result showed that increasing the normal stresses will result in the highest reading in
pull-out capacities. Also, the given thickness of sand has provided useful drainage and
prevented pore pressure build up during pull-out.
Figure 2.5: Arrangement of Pull-out Tests by Abdi and Arjomand, 2011
Figure 2.6: Pull-out Appratus as Used by Abdi and Arjomand, 2011
-
15
2.6 Finite Element Modelling (FEM)
Khedkar and Mandal, 2009 studied the interaction of pull-out test with different height
of cellular reinforcement along with planar sheet reinforcement which carried out under
two different normal pressure of 75 kPa and 100 kPa. In their studies, the interactions
of cellular reinforcements in pull-out test was compared with the results obtained from
finite element method application using PLAXIS software as shown in Figure 2.7 and
Figure 2.8. The analysis of dimension optimization for cellular reinforcement is done
and found that the optimum longitudinal spacing to height ratio is to be 3.3. Also, pull-
out capacity was found to have increased with increasing height of cellular element.
Figure 2.7: Finite Element Modelling (FEM) of a Pull-out Test by Khedkar and
Mandal, 2009
-
20
Figure 3.1: Location of Pull-out Test Site
Figure 3.2: Pull-out Test Concrete Box
-
21
3.2 Materials for Pull-out Tests
3.2.1 Strips
The strips used in this research are shown in laboratory photos of Figure 3.3 and 3.4.
The strips were all fabricated in-house in the laboratories of the School of Civil
Engineering and the School of Mechanical Engineering. Geometric specifications of
strips designed for pull out tests are given in Table 3.1 while properties of strip and
anchorage elements are given in Table 3.2. Each strip may consist of longitudinal
member, such as anchorage elements, stiffeners, and welding, which will be described
next.
Figure 3.3: Strips in Lateral View
-
22
Figure 3.4: Strips in Longitudinal View
Table 3.1: Geometric Specifications of Strips Designed for Pull-out Tests
No
Geometric specifications
(subscripts showing dimensions length, width, and thickness in cm)
Height
of
element
s
(cm)
No. of
eleme
nts
(n)
1 PL60050.5cm 0 0
2 PL60050.5cm + 6PL510.5cm[element] + 6PL410.5cm[stiffener] 1 6
Table 3.2: Properties of Strips and Anchorage Elements
Property Value
Density, 7850 kg/m3
Elasticity modulus, E 200 GPa
Poisson ratio, v 0.3
-
27
3.4 Experimental Programs
3.4.1 Compaction Test
The compaction tests were carried out in accordance with ASTM D1557 (ASTM,
2007b). This laboratory test is called Modified Proctor Test and the equipment used is
shown in Figure 3.8. This test was conducted to obtain the maximum dry unit weight of
compaction and the optimum moisture content. The sand was sieved by No. 4 sieve
(4.75 mm) and placed in the mould having a volume of 944 cm3. The sand was then
compacted in five layers by a hammer that has a mass of 4.54 kg. The drop of hammer
was 457 mm and the numbers of hammer blows were 25 per layer, evenly over the area
in the mould.
Figure 3.8: Compaction Test Equipment
-
29
Figure 3.10: Tensile Test Equipment
Two tensile tests were carried out on the strips used in this research, which were plain
strip and strip with 1 cm anchorage elements. Each strip used in the test was 100 cm
length, 5 cm width, 0.5 cm thickness. The rate of tension was 18 mm/min. The strips
were expected to yield the same tensile strength as their dimensions were same.
However, there was a possibility that the work of attaching anchorage elements and
stiffeners could affect the tensile strength due to disturbance that might have been
inflicted upon the otherwise plain and perfect strips. Figure 3.11 shows the condition of
the strip after the tensile test.
-
30
Figure 3.11: Strip Broken after Tensile Test
3.4.3 Pull-out Tests
The set-up of the pull-out test is shown in Figure 3.12. The components seen were
concrete test box, bricks, hydraulic jack, displacement transducers, load cell, data
logger, and laptop computer.
Figure 3.12: The Overview of the Pull-out Test
-
31
The dimensions of the concrete test box was 10 m 1 m 0.75 m. The soil was first
placed inside the concrete box until 0.8 m high where compactions were done for each
0.2 m of soil layers. The compaction process was done uniformly by using the plate
compactor as shown in Figure 3.13.
Figure 3.13: Compaction Process by Using Plate Compactor
After the strip was placed, the soil was filled until the top of concrete box, levelled and
compacted again before bricks were laid on top of it. The rear hole of strip was
connected to the SDP-C displacement transducer by using stainless steel wire rope, as
shown in Figure 3.14, whereas the front hole was connected to the pulling rod that
pulled by hydraulic jack.
-
32
Figure 3.14: Rear Displacement Transducer
The pulling rod and the hydraulic jack were assembled into a steel frame in the front
face of the box as shown in Figure 3.15 where the displacement of the pulling rod was
monitored using CDP displacement transducer. The pull-out force was created by
hydraulic jack and was monitored by using a load cell. The load cell which calibrated
properly was used to measure the pull-out force of the reinforcement strip. The
maximum pull-out force which could be measured by the load cell was 44.48 kN. The
CDP displacement transducer is shown in Figure 3.16 and the load cell is shown in
Figure 3.17.
-
33
Figure 3.15: Steel Frame Consisting of Pulling Rod, Load Cell, Hydraulic Jack, and
Front Displacement Transducer
Figure 3.16: Front Displacement Transducer
-
34
Figure 3.17: Load Cell Used to Monitor Pull-out Capacity
The data from the load cell, front and rear displacement transducers were transmitted to
a fully configurable data logger which interfaced with the laptop computer and utilized
software WINHOST to view and analyse the collected data. For the pull-out tests, it
was programmed to record data for every 0.25 second. The data logger used in the test
is shown in Figure 3.18.
Figure 3.18: Data Logger Used for the Pull-out Tests
-
36
Figure 3.19 shows an example of 6 layers of bricks. Approximately 1218 bricks were
used for 6 layers of bricks to simulate normal stress of 8.25 kPa.
Figure 3.19: Example of 6 Layers of Bricks
3.5 Finite Element Analysis
The pull-out capacity of the reinforcement strip was simulated and assessed by the
finite element model. The obtained results were then compared with the results of field
pull-out tests.
The numerical analysis of the pull-out tests was prepared using the software package
PLAXIS 2D AE, as shown in Figure 3.20. This software employs a commonly-used
finite element code for geotechnical engineering problems. The pull-out tests were
simulated as a 2D problem having 15 nodes (i.e. 2D elements). In general, about 5000
elements and 40000 nodes were generated for every pull-out analysis in the PLAXIS
software.
-
37
Figure 3.20: PLAXIS 2D AE Software
To simulate the field pull-out tests, the geometry of the test box was modelled such that
it was similar to that of the real test box. The bottom boundary was modelled with total
fixity, whereas the side boundaries were fixed horizontally. In this study, in order to
model the sand, it was decided to use the non-linear Mohr-Coulomb criteria due to their
simplicity, practical importance and the availability of parameters needed. The
properties of the sand and the reinforcement strips used in both the field tests and
numerical analysis were exactly identical. Normal pressure was modelled by a vertical,
uniformly-distributed load on top of the sand layer. The displacements obtained from
the field results were then assigned as the prescribed displacements in horizontal
direction.
For this FEM analysis, 6 model were generated for both plain strip and strip with 1 cm
anchorage elements that having normal pressure 4.25 kPa, 8.50 kPa, and 12.75 kPa.
-
39
Figure 3.21: Methodology Adopted in this Research
Start
Desk study
1. Sieve analysis 2. Compaction tests 3. Tensile tests
Pull-out tests
1. Plain strip
2. Strip with 1 cm anchorage elements
FEM analysis
End
-
44
Figure 4.4: Pull-out Force versus Front and Back Displacements for Plain Strip under
Normal Stress of 4.25 kPa
Figure 4.5: Pull-out Force versus Front and Back Displacements for Plain Strip under
Normal Stress of 8.50 kPa
0
0.5
1
1.5
2
2.5
3
0 10 20 30 40 50 60 70 80 90
Pu
llou
t fo
rce
(KN
)
Displacement (mm)
Back Force-Displacement
Front Force-Displacement
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70
Pu
llou
t fo
rce
(KN
)
Displacement (mm)
Back Force-Displacement
Front Force-Displacement
-
45
Figure 4.6: Pull-out Force versus Front and Back Displacements for Plain Strip under
Normal Stress of 12.75 kPa
Figure 4.7: Pull-out Stress versus Normal Stress for Plain Strip
0
2
4
6
8
10
12
14
0 10 20 30 40 50 60 70 80
Pu
llou
t fo
rce
(KN
)
Displacement (mm)
Back Force-Displacement
Front Force-Displacement
-
47
Figure 4.8: Pull-out Force versus Front and Back Displacements for Strip with 1 cm
Anchorage Elements under Normal Stress of 4.25 kPa
Figure 4.9: Pull-out Force versus Front and Back Displacements for Strip with 1 cm
Anchorage Elements under Normal Stress of 8.50 kPa
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30 35 40 45 50
Pu
llou
t fo
rce
(KN
)
Displacement (mm)
Back Force-Displacement
Front Force-Displacement
0
2
4
6
8
10
12
14
16
0 10 20 30 40 50 60 70 80
Pu
llou
t fo
rce
(KN
)
Displacement (mm)
Back Force-Displacement
Front Force-Displacement
-
48
Figure 4.10: Pull-out Force versus Front and Back Displacements for Strip with 1 cm
Anchorage Elements under Normal Stress of 12.75 kPa
Figure 4.11: Pull-out Stress versus Normal Stress for Strip with 1 cm Anchorage
Elements
0
5
10
15
20
25
0 10 20 30 40 50 60 70 80 90
Pu
llou
t fo
rce
(KN
)
Displacement (mm)
Back Force-Displacement
Front Force-Displacement
-
50
Figure 4.12: Pull-out Force versus Displacement for Plain Strip and Strip with 1 cm
Anchorage Elements under Normal Stress of 4.25 kPa
Figure 4.13: Pull-out Force versus Displacement for Plain Strip and Strip with 1 cm
Anchorage Elements under Normal Stress of 8.50 kPa
0
1
2
3
4
5
6
7
8
9
10
0 10 20 30 40 50 60 70 80 90
Pu
llou
t fo
rce
(KN
)
Displacement (mm)
Plain Strip
Strip with 1 cm anchorage elements
0
2
4
6
8
10
12
14
16
0 10 20 30 40 50 60 70 80
Pu
llou
t fo
rce
(KN
)
Displacement (mm)
Plain Strip
Strip with 1 cm anchorage elements
-
51
Figure 4.14: Pull-out Force versus Displacement for Plain strip and Strip with 1 cm
Anchorage Elements under Normal Stress of 12.75 kPa
Red lines (strip with 1 cm anchorage elements) in all cases were noted to have higher
values than blue lines (plain strip). According to Mosallanezhad (2014), adding anchors
to the conventional strip increases the interaction between the soil and the
reinforcement by about 340%. In this case, the result shows that attachment of
anchorage elements can increase the pull-out capacity by at least 46.43%. This also
proven that attachment of anchorage elements significantly increased the frictional
angle between reinforcement and soil which resulted in higher pull-out capacity which
complied to the statement by Mosallanezhad (2014).
0
5
10
15
20
25
0 10 20 30 40 50 60 70 80
Pu
llou
t fo
rce
(KN
)
Displacement (mm)
Plain Strip
Strip with 1 cm anchorage elements
-
55
4.3.1 Deformed Mesh
Figure 4.17: Deformed Mesh Generated for Plain Strip
Figure 4.18: Deformed Mesh Generated for Strip with 1 cm Anchorage Elements
-
57
4.3.2 Axial Force
Figure 4.19: Pull-out Force on Plain Strip under the Prescribed Displacement 18.42 mm
Figure 4.20: Pull-out Force on Strip with 1 cm Anchorage Elements under the
Prescribed Displacement 67.22 mm
-
59
4.3.3 Zones of Horizontal Displacements
Figure 4.21: Zones of Horizontal Displacement, ux Surrounding the Plain Strip
Figure 4.22: Zones of Horizontal Displacement, ux Surrounding the Strip with 1 cm
Anchorage Elements
-
61
4.3.4 Zones of Shear Stresses
Figure 4.23: Shear Stress Zones Surrounding the Plain Strip
Figure 4.24: Shear Stress Zones Surrounding the Strip with 1 cm Anchorage Elements
-
63
4.3.5 Total Principal Stresses
Figure 4.25: Stress Points Showing Principal Stresses Surrounding the Plain Strip
Figure 4.26: Stress Points Showing Principal Stresses Surrounding the Strip with 1 cm
Anchorage Elements