Journal of Civil Engineering and Urbanism  
Volume 9, Issue 1: 01-06; Jan 25, 2019  
ISSN-2252-0430  
The Study of Failure Mechanism of Reinforced Soil  
under Strip Foundation by PIV Method  
Forough Ashkan  
Department of Civil Engineering, Faculty Member of Engineering, University of Maragheh, Iran  
Corresponding author’s Email: ashkan@maragheh.ac.ir  
ABSTRACT  
In the history of the technology of building materials, soil as a mass with shear and compressive strength is well  
known but not much resistance stretching. To compensate for this deficiency in the soil of the materials as a kind of  
Geosynthetic reinforced are usually are used. The main objective of this study reviews how to change to forms in  
soil and its mechanisms can be disruptive. In order to study the pattern of change in soil and created the following  
forms and how to influence it is armed on the laboratory scale model is also disruptive and physical features (speed  
measurement of particle image) is used. According to the obtained results were observed due to the tendency of  
loose dirt to the density, soil elements relative to the following meeting of the Conference, much less. As well as the  
effect of the angle number placement on the amplifier elements and elements was investigated. View was that by  
increasing the number of layers is a meeting of the armed elements of the territory against non-State armed groups  
sought the meeting to have been armed with a layer mode and more. According to the angle of the anchor elements  
relative to the horizon can be seen that the level of fissures created in the armed mode with two other more than in  
two layers, in the direction of the longitudinal and cross-section has been extensive.  
Keywords: Reinforced soil, Physical modeling, Visual, Disruptive mechanism, PIV method.  
INTRODUCTION  
disruptive of wedge and armed with a width (  
)
B  B  
and the level-up areas of the Earth's surface ruptures finds  
development. The method presented is based on analytical  
studies and is now also laboratory is based on modeling.  
Most physical models based on data findings do force-is  
based on the following shift and usually the view is  
disruptive mechanism problem. Due to the complexity of  
the behavior of the soil that leads to the complexity of the  
interaction of soil and will be armed, a review of the  
behavior of reinforced soil deformation under the  
successive experimental tape cut makes it possible to  
understand the true mechanism of deformation or be  
disruptive.  
One of the important factors in the design of structures  
such as buildings, followed by bridge & dam is properly  
evaluated the role of stress-deformation behavior of soil  
under the Foundation. This factor depends on the  
mechanical characteristics of the soil. Karl von Terzaghi  
(1943) was the first theory to calculate the bearing  
capacity of the Foundation presented the final surface.  
The shear fissures Terzaghi beneath the surface of the end  
times is the same as Figure 1 tape a bedrock premise.  
He has also replaced available soil at the top of the  
) overhead. (  
underlying bedrock surface with (  
Is gravity Specific of soil)  
q Df  
This research enables us to examine the behavior of  
reinforced soil under different parameters and how to  
influence this parameter on slip surfaces created times  
compare over share.  
The following soil to bedrock fissures in the area  
three separable area:  
1. triangular area immediately below the Foundation  
(wedge disruptive).  
2. Radial shear regions of the ADF and the CDE  
with curved fissures DF and DE.  
3. Two Rankin-triangular area AFH and CEG.  
In the case of reinforced soil disruptive mechanism,  
Huang and Menq (1997) proposed a theory based on the  
mechanism of failure of Wide-slab in the territory as  
shown in Figure 2. According to this theory the next  
Figure 1. The ultimate in bearing shear fissures a rigid  
rough contact surface with tape infrastructure  
To cite this paper: Ashkan F (2018). The Study of Failure Mechanism of Reinforced Soil under Strip Foundation by PIV Method. J. Civil Eng. Urban., 9 (1): 01-06.  
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cell with 250kg capacity was used to measure the entering  
loads. In this case study, load cell was fastened by the bolt  
in the metal plate center that formed solid system. This  
solid system was placed exactly under vessel and under  
forcing system. For measuring the foundation settlement  
one displacement sensor (LVDT) was used that placed on  
and center of metal plate. The present research includes  
four loading tests.  
To reinforce soil foundation two reinforced geogride  
and geotextile were used. The various tests parameters  
include: reinforced types (geogride and geotextile),  
reinforcement layer (N), depth of first layer (U),  
reinforcement wide (b) and space between reinforcement  
layers (h). Table 2 shows the features of testing models.  
Figure 2. Failure mechanism the Wide-slab of reinforced  
soil under the foundation strip.  
MATERIAL AND METHODS  
Characteristics of the physical model  
On the research of the soil dry sand was used as a  
test case. To determine the profile of gravel, particle  
experiments in accordance with the standard ASTM D  
422-87, Specific gravity in accordance ASTM D 854-87  
Were done. The sand contains. 002% decline from the  
number 200 sieve, as Sandy has been classified a bad  
seed. Other soil parameters is given in table 1. In relation  
to how to sand r, to create uniform models for use with  
loose gravel, sand and rain from a height of about 25 cm  
was poured.  
Table 1. Specifications of used sand  
gr /cm3  
Cu  
Cc  
Gs  
27  
2.67  
1.5  
1.25  
0.992  
Figure 3A shows the model and test case parameters  
and shows the manner of reinforcing soil foundation. For  
entering load, one rigid frame was designed and installed  
in the laboratory. First, one reinforced concrete bond  
foundation with 1.8m length, 0.40m width and 0.50m  
height was made and at the two ends of this foundation.  
The column base plate besides the six built were placed to  
stablish the columns. In this way, beam and column nodes  
were designed. As you can see in the figure 3 for  
connecting columns two UNP160 hopper was used and  
for beam, two UNP200 hopper node. Has been used and  
then, beam and column we strengthen by the band. Figure  
(3B) shows the supported structure of forcing system. For  
building the laboratory vessel that soil should be put on it,  
the metal plates with 3.9mm thickness and dimension of  
(1.0*0.3*0.6) m was used. Because of the photography,  
this system was formed with the case that has 3cm  
transparent talc to take photo in successive loadings.  
The tool for loading in system is force controlling  
that by increasing the weights until interruption time, the  
sample has been increased. Due to the decreasing of  
loading from forcing system, lever load practice was used  
that has 1.1m*0.03m arm and has 0.03m thickness which  
the 3kg weight was installed at one side to make  
equilibrium of the system. The space between weights to  
loading place is 0.75cm; therefore, the amount of loads  
9.3 times increases in every loading. Figure 4 shows the  
schematic picture of loading system and types of supports.  
To transfer the entering force to tested soil, one rigid  
plate with the size of 0.3m*0.061m was used that work as  
a surface band foundation on soil bed. One digital load  
Calibration point  
A)  
B
b
Surface  
P
u
Reinforcement layer No.1  
Reinforcement layer No.2  
Reinforcement layer No.3  
h
h
H
Rigid base  
B)  
Figure 3. A) the model and test case parameters; B) the  
supported structure of forcing system and laboratory  
vessel  
To cite this paper: Ashkan F (2018). The Study of Failure Mechanism of Reinforced Soil under Strip Foundation by PIV Method. J. Civil Eng. Urban., 9 (1): 01-06. www.ojceu.ir  
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Hang the frames reaction  
Load cell  
110 cm  
75 cm  
3kg  
9 cm  
Figure 4. The schematic picture of loading system and types of supports  
Table 2. The features of testing models  
Loading by weight  
Test number  
1
2
3
4
Reinforcement  
Geotextile  
Geotextile  
Geotextile  
Unreinforced  
N
2
1
8
1
-
-
b/B  
11  
11  
u/B  
h/B  
5.0  
5.0  
5.0  
-
5.0  
-
-
-
Calibration  
factor  
5.5ꢁ3  
5.2ꢀꢀ  
5.588  
5.21ꢀ  
Image processing (picture processing)  
(A)  
During the test by using PIV pictorial method that  
was utilized in fluid mechanic by Adrian (1991) in  
experimental studies for first time and recently was used  
by White et al. (2001-2003) for geotechnical modeling  
and for studying soil changings, the photos were taken of  
soil mass that had been changing with the digital camera  
with 7.1 mega pixel (3072*2304) clearness and these  
images were stored in computer memory and after tests,  
they were processed pictorial with the Geopiv8 software.  
These images divides to different tracks to process by the  
PIV methods and each track has special image tissue and  
this fact causes to determine the exact place of other  
images and it shows the tracks displacements (White et  
(A)  
The results of place changings of tracks in different  
pictures are in pixel unit and for changing to millimeter  
calibration factors are needed. These factors are placed in  
definite spaces with black color on the window  
(millimeter). The place of each calibration factor was  
determined by the close ranged photogrammetry and with  
regard to fixed spaces and fixed calibration factors during  
tests it can be transferred the tracks coordinates to the real  
places by using that calibration factors. The displacement  
vectors charge from picture to real spaces by close ranged  
photogrammetry and the soil plate displacement square  
will be obtained. In this research, by meshing the obtained  
pictures to the tracks (48*48), the suitable tissue for  
analysis was developed and the tracks displacement in soil  
masses in changing ways were obtained.  
(B)  
For example figure 5A shows the foundation  
settlements and curved shear displacement vectors on  
weak sands with the 10mm (s/b=0.18) (s stands for the  
settlement) settlement and it shows that in test1  
reinforcement lays are place in Z/B=0.5. Displacements  
vectors inclined to downward the foundation because the  
soil is weak and it indicate the soil density under  
foundation.  
(B)  
Figure 5: The foundation settlements and curved shear  
displacement vectors. )A(: S/B=0.18, )B( :S/B=0.5  
To cite this paper: Ashkan F (2018). The Study of Failure Mechanism of Reinforced Soil under Strip Foundation by PIV Method. J. Civil Eng. Urban., 9 (1): 01-06. www.ojceu.ir  
3
In left hand of figure 5A, aggregate curvature was  
developed and extends to Z/B=1 depth. This curvature  
was observed in width under reinforcement layers with the  
Geotextile , N=1 , b/B=11, u/B=0.5  
Element Settlement (mm)  
0
5
10  
15  
20  
25  
-1<(X/B)  
<1.  
Also,  
figure  
5B  
shows the  
0
5
Z/B=0.502 , X/B=-0.0101  
Z/B=1.056, X/B=-0.0101  
Z/B=1.5407 , X/B=-0.0101  
Z/B=2.0254 , X/B=-0.0101  
Z/B=2.5102 , X/B=-0.0101  
Z/B=3.0641 , X/B=-0.0101  
displacements vectors shear curvatures of the band  
foundation settlements that are the size of 30min(s/b=.5).  
It can be seen that with settlement increasing  
disconnected wedges are formed under reinforcement  
layers while in low settlements there are no disconnected  
wedges and there are no radius and firm shearing in this  
aggregate curved settlement was developed until the depth  
of z/b=2.5.  
10  
15  
20  
25  
30  
35  
Also shear curved density that refers to existence of  
slip surface was seen under reinforcement layers.  
(C)  
unreinforced  
Element Settlement (mm)  
0
2
4
6
8
10  
RESULTS  
0
5
Z/B=1.1602 , X/B=0.0516  
Z/B=1.4907 , X/B=0.0516  
Z/B=1.9864 , X/B=0.0516  
Z/B=2.4821 , X/B=0.0516  
Z/B=2.9779 , X/B=0.0516  
Z/B=4.1346 , X/B=0.0516  
In all settlement tests, LVDT was used for measurement s  
and PIV analysis was used for determining the vertical  
and horizontal different parts of the soil. Figure (6A)  
shows the amount of horizontal trans for motions versus  
the amount of vertical transformations that were  
developed in various places of foundation that was  
observed in test1 with the reinforced geotextile layer (X is  
the space of function and Z is the depth).  
10  
15  
20  
25  
30  
35  
(D)  
Figure 6. The soil elements settlement versus foundation  
settlement  
Geotextile , N=2 , b/B=11, u/B=0.5 , h/B=0.5  
Element Settlement (mm)  
As it can be seen, on the identical foundation  
settlement were decreased and in low depth the soil  
elements settlement was very lower than the foundation  
settlement, because the sand soil is very weak and it  
inclined to the density under foundation in increasing  
loads.  
Figure (6B) shows the soil elements settlement  
versus foundation settlement that is for test1 and it is  
Z/B=2.0673 and X/B =0, 0.5 and 1. It was observed that  
in identical depth, by increasing the space of foundation  
center the soil element settlement was decreased relatively  
to the foundation settlement.  
0
5
10  
15  
20  
25  
30  
0
5
Z/B=0.5306 , X/B=-0.0152  
Z/B=1.0428 , X/B=-0.0152  
Z/B=1.5551 , X/B=-0.0152  
Z/B=2.0673 , X/B=-0.0152  
Z/B=2.5064 , X/B=-0.0152  
Z/B=3.0187 , X/B=-0.0152  
10  
15  
20  
25  
30  
35  
40  
(A)  
Figure (6C) shows the graphs of soil elements  
settlement with reinforcement layer (test3). It was  
observed that with identical foundation settlement with  
depth increasing, the soil element settlement was  
decreased and the amount of settlement relative to  
reinforced manner with two layers was small. Also, in  
unreinforced manner in figure (6D), the amount of  
settlement was too small. In reinforced manner with two  
Geotextile , N=2 , b/B=11, u/B=0.5 , h/B=0.5  
Element Settlement (mm)  
0
5
10  
15  
0
Z/B=2.0673 , X/B=-0.0152  
Z/B=2.0673 , X/B=-0.5275  
Z/B=2.0673 , X/B=1.0093  
5
10  
15  
20  
25  
30  
35  
40  
layers  
the  
extensive  
range  
of  
soil  
was  
transformed because the reinforced layers were increased  
and it affect the lower depth of soil elements but in  
reinforced manner with one layer and it unreinforced  
manner, the surface shearing is smaller than the reinforced  
manner with two layers; therefore, the lower elements are  
affected by this displacement.  
(B)  
To cite this paper: Ashkan F (2018). The Study of Failure Mechanism of Reinforced Soil under Strip Foundation by PIV Method. J. Civil Eng. Urban., 9 (1): 01-06. www.ojceu.ir  
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For transformation studies and soil element  
displacement under and around the foundation, the  
placement vectors angles were used. With regard to the  
vectors angles of elements under different depth of  
foundation and toward the horizontal on the figure7, it can  
be seen that how the displacement of band foundation was  
very different in reinforced soil with one geotextile layer  
and two geotextile layers with unreinforced manner which  
in one layer of reinforced (figure 7A), displacement  
vectors on the depth of Z/B=1 , X/B=1.25 were  
transformed on upper orientation and in Z/B=1.5,  
displacement vectors transformed to horizontal manner  
and in lower depth they close to each other in vertical  
manner.  
Geotextile , N=2 , b/B=11 , u/B=0.5 , h/B=0.5  
Z/B=1.5  
100  
80  
60  
40  
20  
0
Z/B=2  
Z/B=2.5  
Z/B=3  
-20  
0
0.25 0.5  
0.75  
1
1.25 1.5 1.75  
2
2.25 2.5  
X/B  
(B( test 1  
Unreinforced  
This situation was different for two layer reinforced  
soil (figure 7B) which in approximate depth of Z/B=1 and  
X/B=1.8 displacement oriented to upper level and  
gradually with increasing depth on Z/B=2 they close to  
horizontal manner. In unreinforced manner on Z/B= 1 and  
X/B=1.3 the soil elements move to upper level and  
gradually close to horizontal manner with increasing of  
Z/B and in figure (7C) it can be seen that in all three cases  
with increasing the depth of placement angles, they close  
to the horizontal manner.  
100  
80  
60  
40  
20  
0
Z/B=1  
Z/B=1.5  
Z/B=2  
Z/B=2.5  
Z/B=3  
-20  
-40  
0
0.5  
1
1.5  
2
2.5  
3
3.5  
4
X/B  
)C( test 4  
Figure 8 shows the formed wedge in reinforced soil  
with one geotextile layer and also it shows the  
disconnected surface. The dark line of reinforced shows  
the geotextile layers before transformation. It is observed  
that the displacement vectors side under the reinforced  
layer is downward. The vectors sizes are larger in this  
parts that cause the reinforced layers to be transformed  
under the foundation. In radius shear regions and in  
strengthened regions it moves to upper level. On upper  
levels of reinforced layer, the displacement vector angles  
are not corresponding with below layers. On the geotextile  
layer, the disconnected situational surface was developed  
which are shown with blue colored lines. Gradually with  
increasing the depth of moving vectors to downward, the  
sizes of them are decreased.  
Figure 7. The vectors angles of elements toward the  
horizontal  
Also, in supported cases, the disconnected surfaces  
reached on the below reinforcement layer but it does  
not transfer to the earth. With regard to this graph it is  
known that the Huang and Menq theory is not correct.  
Figure 8. The formed wedge in reinforced soil (2)  
Geotextile , N=1 , b/B=11 , u/B=0.5  
100  
CONCLUSION  
Z/B=1  
75  
50  
25  
0
Z/B=1.5  
Z/B=2  
By using PIV method, the disconnected surface was  
depicted for different tests. On the basis of observed  
results the displacements victors and reinforced  
foundation disconnected mechanism were considered and  
the obtained results are follows:  
Z/B=2.5  
Z/B=3  
-25  
-50  
0
0.25  
0.5  
0.75  
1
1.25  
1.5  
1.75  
2
1. In this research it is shown that the formed  
disconnected wedge under the foundation are not  
correspond to the Huang and Menq theory.  
X/B  
)A( test 3  
To cite this paper: Ashkan F (2018). The Study of Failure Mechanism of Reinforced Soil under Strip Foundation by PIV Method. J. Civil Eng. Urban., 9 (1): 01-06. www.ojceu.ir  
5
2. It is obvious that the reinforcement effects depend  
on the number of layers and the condition of the tests. In  
useful application, two reinforcement layers are suitable  
because the loading capacity increases with regard to the  
number of layers.  
3. The soil elements settlement in proportion to  
foundation settlement is loss because weak soil inclined to  
be dense. Also the placement angles of displacement  
vectors increase with the increasing of depth and it close  
to vertical manner. On top of the geotextile layer which  
the vectors orientation has been changed, the angles are  
negative. in reinforced manner with two layers,  
displacement vectors in depth of Z/B=1 and X/B=1.25  
transformed to upper level but in reinforced manner with  
two layers in depth of Z/B=1.5 and X/B=1.8 the  
displacement oriented to upper level that shows the  
extensive disconnected surface in both horizontal and  
vertical sides of two layer reinforcements.  
DECLARATIONS  
Authors’ Contributions  
All authors contributed equally to this work.  
Competing interests  
The authors declare that they have no competing  
interests.  
REFERENCES  
Adrian J (1991). Department of theoretical and applied  
mechanics, University of Illinois,Urbana, Illinois  
61801.  
Huang CC and Menq FY. (1997). "Deep footing and  
wide-slab effects on reinforced sandy ground".  
Journal of Geotechnical and Geoenvironmental  
Engineering, ASCE 123 (1), 3036.  
Terzaghi K (1943). Theoretical Soil Mechanics. Wiley,  
Inc., New York.  
White DJ and Richards, and Lock AC (2004). "The  
measurement of landfill settlement using digital  
imaging and PIV analysis ". Schofield Center,  
Department of Engineering, University of  
Cambridge, UK.  
White DJ and Take WA and Bolton MD (2003). "Soil  
deformation measurement using particle image  
velocimetry  
(PIV)  
and  
photogrammetry".  
Géotechnique 53, No. 7, 619-631.  
To cite this paper: Ashkan F (2018). The Study of Failure Mechanism of Reinforced Soil under Strip Foundation by PIV Method. J. Civil Eng. Urban., 9 (1): 01-06. www.ojceu.ir  
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