main thesis version final
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MSc Geotechnical Engineeing
FRICTIONAL SURFACE BETWEEN CONSTRUCTION MATERIAL
AND GRANULAR SOILS
(EFFECT OF SURFACE ROUGHNESS ON SHEAR STRENGTH)
Sepehr Aghamehdi
1067376
Dissertation submitted is in partial fulfilment of the degree of Master of
Science.
School of Civil Engineering
University of Birmingham
1st May 2015
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Abstract
Assessments of interface friction parameters between soil aggregates and
construction materials (which in this study steel mesh was used) were conducted to
measure the shear strength of the soil and look into how the shear stress and
frictional resistance of the soil can be effected by using different void ratios and
densities.
This study will look into how also the material surface roughness affects the soil
frictional resistance of the soil.
In order to determine the shear stress and hence the angle of friction, whether
internal or interface, direct shear tests were conducted using variety of normal
stresses, 50kpa, 100kpa and 200kpa, to evaluate how the soil’s shear strength is
affected by different normal stresses. The soil used was construction aggregates
with grain sizes of 2mm used to carry out the tests.
The construction material as mentioned were steel meshes which spanned 10mm x
10mm and an overall span of 100mm x 100mm which could fit into the shear box.
These meshes had a variety of depths of 2mm, 4mm and 6mm which was made
available by welding the steel meshes together.
By evaluating and observing the graphs made by author, of shear stress-horizontal
displacement considering how by keeping void ratios and normal stresses constant
and variable at different points, it came to the attention that by doing to shear
strength of the soil is affected almost substantially by these factors, for instance:
From shear stress and horizontal displacement graphs considering constant
void ratio and variable normal stresses, it was understood that as the normal
stress increases, shear stresses increase.
However by rearranging the graphs by considering constant normal stresses
and variable void ratios, it could be observed that shear stress increases as
the void ratios decrease (density increases), hence the density has a massive
impact on shear stress and frictional resistance manipulation.
From the shear envelopes, it was noticed that by decreasing the friction angle
(although it fluctuates from time to time) the shear stress increases.
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The shear strength of soil is always higher compared to the interface friction
angle between the soil and construction material.
However, although that this study has helped to understand, how different factors
affects the shear strength and frictional resistance of the soil, one of which is surface
roughness and how important and vital it is, future work is required for more
information on, for example, how much of steel mesh’s depth need to be increased
(rougher surface), so that the shear failure plane could get pushed back into the soil,
which provides a higher shear strength as the soil always has the highest shear
strength. Other factors that can be taken into account are moisture content and
variety of grain sizes and different angularity of the grains.
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Contents Abstract ................................................................................................................................................... i
Acknowledgements ............................................................................................................................. iv
1. Introduction .................................................................................................................................... 1
1.1. Objectives .............................................................................................................................. 1
1.2. Outline of study ..................................................................................................................... 1
2. Literature Review ......................................................................................................................... 2
3. Experimentation (Direct Shear Test) ......................................................................................... 6
3.1. Soil properties and classification: ...................................................................................... 6
3.2. Sieve Analysis ....................................................................................................................... 9
3.3. Type of construction material ........................................................................................... 11
3.4. Direct Shear test procedure .............................................................................................. 14
4. Discussion of Results ................................................................................................................ 20
4.1. Constant void ratio vs variable normal stress ................................................................ 21
4.2. Constant normal stress vs variable void ratio ................................................................ 26
4.3. Shear failure envelope ....................................................................................................... 32
4.4. Dilatency of tested granular material ............................................................................... 36
4.5. Void ratio (e) and friction angle (ϕ) ....................................................................................... 46
5. Conclusion ................................................................................................................................... 48
6. Appendices .................................................................................................................................. 49
A. Relationship between the shear stress and the horizontal displacement for all
soil/material interactions with e = 0.5 as well as a graph for the comparison of all curves
with similar void ratio. .................................................................................................................... 50
B. Relationship between the shear stress and the horizontal displacement for all
soil/material interactions with e = 0.8 as well as a graph for the comparison of all curves
with similar void ratio. .................................................................................................................... 55
C. Graphs to show the comparison of all relationships between the shear stress and
the horizontal displacement for all soil/material interactions with similar normal stress and
variable void ratios. ........................................................................................................................ 60
D. Relationship between the vertical movement and the horizontal displacement for all
soil/material interactions with e = 0.5 as well as a graph for the comparison of all. ............ 63
E. Relationship between the vertical movement and the horizontal displacement for all
soil/material interactions with e = 0.8 as well as a graph for the comparison of all. ............ 69
F. Coulomb failure envelopes for all soil/material interactions with e = 0.5. ...................... 75
G. Coulomb failure envelopes for all soil/material interactions with e = 0.8. .................. 77
7. Reference .................................................................................................................................... 79
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Acknowledgements
I would like to express my gratitude to Dr. Ghataora for his invaluable support and
guidance throughout this research program. Also I would like to thank my family for
their patience and their unconditional love, who without them this study would not
have been possible. Also my good friend/ colleague Hamid Sadeghi for his
irreplaceable assistance throughout this project.
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1. Introduction Interaction between the construction materials and the soil is of a particular
importance in Geotechnical engineering, this has a major significance in soil
structure interaction problems such as retaining structures, foundations whether
deep or shallow, soil samplers, soil and geomembrane interface strength and the
stability of mechanically stabilised structures.
The strength of this interface known as shear surface between the two materials is
governed by the type of finish on the concrete surface or other construction
materials; whether it is smooth or rough which will have a massive impact on the
friction angle that describes the ability of the material to shear which is essential for
the stability of the structure such as foundations.
Granular materials are preferred for structural fill because they are strong, drain
water rapidly, and settle relatively little (Edil and Benson, 2007) and these are some
of the reasons why granular soil need to be investigated further to widen the
understanding of its shear behaviour.
The most important factors that need to be evaluated which influence the shearing
behaviour of the soils are the internal friction angle, cohesion, interface friction angle
as well as the adhesion factor, soil properties, such as void ratio, density, particle
size distribution (PSD), gradation and the soil grain shapes and sizes, not forgetting
moisture content, soil composition, surface roughness, and normal load.
Laboratory tests play a vital role for the study of the mechanical behaviour of soil-
structure interfaces. Laboratory friction tests with obvious boundary conditions can
provide fundamental information.
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1.1. Objectives
Main objectives of this research are as follow:
Evaluation of internal friction angle of the soil and the interface friction angle
between the soil and the material used.
Behaviour of the soil under shear stress and determining the behaviour of the
shear envelopes between the material used and the soil interface.
Determination of different void ratio of soil and the variables such as density
and its effect on the interface frictional resistance.
Establish the relationship between the horizontal displacement and the normal
stress for soil-soil interface, soil-steel mesh.
Effect of surface roughness on shear strength.
1.2. Outline of study
This research paper discusses the shear strength of soil and the shearing resistance
of the soil-steel mesh interface and the layout is as follows:
Section 1: This is the introduction of the study as well as the main objectives of this
research.
Section 2: Presents the literature review and previous studies, which were carried
out and about the shear strength and frictional resistance.
Section 3: Illustrates and explains the methods used to obtain information such as
using direct shear box test and the procedure and methodology of the tests.
Section 4: The results from the direct shear box test as well as analysing the data
will be presented here.
Section 5: Discussion of the findings from previous chapter.
Section 6: Provides conclusions for the study and further work.
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2. Literature Review
Das (2005) defined shear strength as follow:
“The shear strength of a soil is the internal resistance
per unit area that the soil mass can offer to resist failure
and sliding along any plane inside it”
Essentially the shear strength is the cohesion and frictional resistance
between solid particles of the soil and the failure occurs in a scenario where the
particles of the soil are able to roll and/or slide past one another and it is the
measurement of the soil resistance to deformation by continuous displacement of its
particles.
Shear strength is determined by several laboratory tests, which can as follow
(Das, 2005):
Direct Shear Test (Shear Box Test)
Triaxial Test
Direct Simple Shear Test
Torsional Ring Shear Test
Etc.
Although there are variety of tests to determine the shear strength of soil, but
direct shear test is the most common tests to evaluate the soil.
Gireesha and Muthukkumaran (2011) determined the frictional resistance of
granular soils by carrying out number of direct shear test on the soil as well as
looking at the interface friction resistance and how the surface roughness of different
construction material impacts the shear strength of the soil.
In order to illustrate this phenomenon, number of construction material such
as concrete, steel and wood were used, with different degree of surface roughness
(smooth and rough). The results that were obtained showed that by increasing the
relative density (Dr) of the samples, interface friction angle (𝛿) and internal friction
angle (ϕ) also increased.
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Hence by doing so and considering the ratio of 𝛿/ϕ for all three material, it was
found out that concrete produces higher internal friction angle comparing to the rest,
this comparison and values can be seen in Table 1.
The tests were carried out for both well graded and poorly graded similarly
maximum, minimum and 50% relative density were considered for the comparison;
consequently it showed that the friction angle is affected substantially by different
gradation, grain sizes, relative density (Packing) as well as surface roughness of the
construction materials.
Concrete
Dr Well Graded Poorly Graded
ϕ 𝛿 𝛿/ ϕ ϕ 𝛿 𝛿/ ϕ
Max 40.1 32.1 0.8 36.1 28.8 0.79
50% 38.2 30 0.78 34.8 27.5 0.79
Min 36.6 28.1 0.76 33 25.9 0.78
Steel
Dr Well Graded Poorly Graded
ϕ 𝛿 𝛿/ ϕ ϕ 𝛿 𝛿/ ϕ
Max 40.1 31.5 0.78 36.1 28.7 0.79
50% 38.2 29.6 0,77 34.8 27.2 0.78
Min 36.6 27.5 0.75 33 25.6 0.77
Wood
Dr Well Graded Poorly Graded
ϕ 𝛿 𝛿/ ϕ ϕ 𝛿 𝛿 / ϕ
Max 40.1 30.7 0.76 36.1 28.4 0.78
50% 38.2 29 0.75 34.8 27 0.77
Min 36.6 26.7 0.72 33 25.4 0.76
Table (1): Interface and internal friction angle for different construction material
(Gireesha and Muthukkumaran, 2011).
As it can be seen the gradation, different density and surface roughness has a
massive influence on the final value of the friction angle and essentially the shear
resistance of the soil. For this fact and importance, in 1961, Potyondy used similar
construction material as Gireesha and Muthukkumaran, but with a difference of
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determining the values in strain and stress controlled environment (Shear box), the
stress controlled shear box had a shearing area of 80cm2 and as for the strain
controlled box, it had an area of 36cm2.
The tests carried out by Potyondy, were mostly for determining the frictional
resistance for saturated and dry aggregates with varying grain sizes of maximum
7.5mm and 2.5mm for rough and smooth surfaces respectively.
By doing so, Potyondy acquired values for internal (ϕ) and interface (𝛿) friction angle
through putting the sand under normal stresses of nearly 50 and 150Kpa with dense
packing of the grains, void ratio of 0.66 and the moisture content of 0.8%.
The summary of the findings can be found in the table 2 below.
Materials
50 Kpa 150 Kpa
Dry Saturated Dry Saturated
ϕ 𝛿 ϕ 𝛿 ϕ 𝛿 ϕ 𝛿
Smooth Steel 44 24 39 24 43 24 37 23
Rough Steel 44 34 - - 43 33 - -
Wood parallel to
grain 44 35 39 33 43 33 37 33
Wood at right angle
to grain 44 39 39 34 43 38 37 34
Smooth Concrete 44 39 39 34 43 38 37 33
Rough Concrete 44 44 - - 43 42 - -
Table (2): Interface and internal friction angle for different construction material
(Potyondy, 1961).
As moisture content, normal stress, surface roughness, gradation and etc are
the factors affecting the shear strength of soil; shearing rate of which tests are being
taken has a significant role and impact on shear strength and that was clearly
demonstrated by Al-Mhaidib (2006), in which tests were conducted to evaluate the
effect of shearing rate on the frictional resistance between steel and sand, with range
of shearing rate on the specimen of soil varying from 0.9mm/min down to 0.0048
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mm/min and normal stresses of 50kpa, 100kpa and 150kpa of which these tests
were done using a 100mm x 100mm shear box.
The results showed that by increasing the rate of shear, for both smooth and
rough surface, the maximum shear stress increases. This can be seen in figure 1 in
which it can also be noted that by manipulating the surface roughness, soil will
behave in a way which has a higher shear stress.
Figure 1: Coulomb failure envelopes between sand and Steel, rough and smooth
surfaces, (Al-Mhaidib, 2006).
Having said that, by taking into account the work, which was completed by
Laskar and Dey (2011), it could be clearly seen that by using different surface
roughness; R1, R2 and R3 which is accounted for values of 0.1, 0.2 and 0.3; with
constant normal stress, the shear stress will be influenced and gives a higher value.
The surface roughness values in this study were defined as the ratio of the
steel surface roughness to the mean diameter of grain size D50. The results of these
test and physical properties of the sand used can be seen in the figure 2 and table 3
respectively.
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Sand Properties Value
Particle diameter, D50 0.5
Maximum void ratio 0.88
Minimum void ratio 0.62
Relative density 0.85
Specific gravity 2.65
Table 3: Physical Properties of sand (Laskar and Dey, 2011).
Figure 2: Shear stress/strain curves with different surface roughness factors (Laskar
and Dey, 2011).
3. Experimentation (Direct Shear Test)
In this section direct shear test procedure, type of material used in the
process, soil properties and classification will be discussed in details.
3.1. Soil properties and classification:
Dry aggregates were prepared, throughout the tests conducted to find out the
properties of the soil. The soil came across as very angular and low sphericity.
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Figure 3: Soil grain angularity and sphericity table.
It was revealed that actual maximum and minimum values for void ratios are
0.44 and 0.82 respectively which was calculated by using the value of the maximum
and minimum density of the aggregates of which were 1892kg/m3 and 1495kg/m3
respectively.
𝛾 = 𝜌 𝑥 𝑔
𝑒 = 𝐺𝑠 𝑥 𝛾𝑤
𝛾𝑑− 1
Note: 𝛾 (Unit weight of the soil) = 𝛾𝑑 as the specimen is dry.
g = Gravitation (9.81m/s2)
γw = Unit weight of water
GS = Specific gravity (2.67)
However, the void ratios used to conduct the tests were of two different values
to clearly show the effect of densities on the shear strength of soil. These were 0.5
for the densest and 0.8 for loose state and the values were used to obtain the
maximum and minimum relative density for the aggregates, which produced values
of 0.842 and 0.053 for the densest and loosest state of each test specimen.
𝐷𝑟(%) = 𝑒𝑚𝑎𝑥 − 𝑒
𝑒𝑚𝑎𝑥 − 𝑒𝑚𝑖𝑛
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Where:
emax = soil maximum void ratio
emin = soil minimum void ratio
e = actual void ratio used for the tests
In order to achieve such densities, before tests began, the void ratios were
controlled by having the volume of the soil in the shear box fixed in order to reach
the ideal density in the box and changing the weight of the soil to get the
corresponding void ratio where appropriate.
The apparatus used was 100mm x 100mm direct shear box with a volume of
300mm3, therefore, the method of calculation used to estimate the amount of soil
that can be fitted into the box in occasions whether the construction material are or
not being present, is as follow:
𝑊
𝑉=
𝐺𝑠 𝑥 𝛾𝑤 𝑥 (1 + 𝑤)
(1 + 𝑒)
Where:
W = weight of soil
V = Volume available in the box for the soil to be fitted into
GS = Specific gravity (2.67)
γw = Unit weight of water
e = Void ratio used
Void ratio (e) Soil weight without
construction material (g)
Soil weight with
construction material (g)
Loose state (0.8) 400 178
Dense state (0.5) 450 214
Table 4: Soil weights in shear box for different void ratios.
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3.2. Sieve Analysis
Sieve analysis was undertaken in order to examine the particle size and how
the distribution of the soil is in reality.
The test was analysed by using four different sieves, 5mm, 3.35mm, 2mm and
1.18mm and at the bottom a solid pan was put in order to gather all the leftovers.
Sieves were shaken for 10 minutes for thorough separation and they
contained a sample of 500 g as it can be seen in the figure below.
Figure 4: Sieve analysis
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Hence, by doing so, the percentage of grain finer table was produced,
therefore, used to acquire the particle size distribution (PSD) curve, and the result of
the analysis is illustrated in the table below.
Sieve Size
Retained Cumulative
Pass Percent % Retained
Weight (g)
Retained
Percent %
Cumulative
Weight (g)
Cumulative
Percent %
5 mm 0.00 0.00 0.00 0.00 100.00
3.35 mm 29.40 5.88 29.40 5.88 94.12
2 mm 407.60 81.52 437.00 87.40 12.60
1.18 mm 62.50 12.50 499.50 99.90 0.10
Pan 0.50 0.10 500.00 100.00 0.00
Table 5: The percentage of grain finer.
The Particle Size Distribution curve in figure 5 presented, to illustrate the grain
distribution and hence using the graph to obtain values for D60, D30 and D10 of which
assist the author to classify the soil being used in this study.
Figure 5: Aggregates Particle Size Redistribution curve.
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10
Pe
rce
nt
Pas
sin
g %
Grain Size (mm)
Sieve Analysis
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Moreover, using the curve above, the following information can be obtained:
D60 = 2.6mm
D30 = 2.3mm
D10 = 1.9mm
Taking these into account the values for Cu and Cc can be found using:
Cu = D60
D10=
2.6
1.9= 𝟏. 𝟒 < 6
Cc = 𝐷30
2
𝐷60 𝑥 𝐷10=
2.32
2.6𝑥1.9= 1 < 𝟏. 𝟎𝟕 < 6
Considering British standard, the classification that can take place here is of
Multi graded according to British standards (BS EN ISO, 2004).
3.3. Type of construction material
The type of construction materials used for this thesis were steel meshes
which spanned 10mm x 10mm and an overall spanning of 100mm x 100mm which
could fit in the shear box and they sat on top of wooden blocks in order to form the
bottom half of the shear box.
Steel meshes used to for which to evaluate the interface friction angle
between soil and structures were arranged in three different thicknesses; 2 mm, 4
mm and 6 mm deep; figure 6 below demonstrates the difference in thickness.
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The way that construction material were being prepared for tests were to
place the wooden blocks at the bottom of the shear box then placing each steel
mesh for each test.
The reason behind using meshes with different depth is that, when soil is
being sheared on its own, it has the highest friction angle, which provides a higher
shear resistance. Therefore, by using so, these test will tend to push the failure line
back into the soil, in which it will generate a higher friction angle and hence greater
shear strength. This will be discussed more in detail in the following sections.
Figure 6: Types of steel mesh
used.
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The formation of material inside the box, using different steel meshes can be
seen in figures 7, 8 and 9 below for comparison.
Figure 7: 1 steel mesh.
Figure 8: 2 steel meshes.
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Figure 9: 3 steel meshes.
3.4. Direct Shear test procedure
Direct shear is the simplest method to determine the angle of shear resistance
of soils, which can be evaluated by containing the specimen in a split box and apply
normal stress in order to compress the sample and as the two halves slide on top of
each other, the vertical movement and horizontal movement are being measured in
order to evaluate the shear strength of the soil.
As direct shear tests are normally conducted in drained conditions, the tests
carried out in this study will undergo a same maintained condition.
The shearing rate at which these tests were measured was 1 (mm/min) as it
was considered due to the general guidance for sand and suggestion made by
Bolton (1979), also note that if tested quickly the results will be meaningless.
The test procedure for direct shear test which was taken by the author is as
follows:
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1. Take the split box and unscrew the bolts which hold the parts together, this
can be seen in figure 10 blow.
Figure 10: set up procedure of shear box.
2. Place the steel plate at the bottom of the bottom half, depending on
whether it is a test where the soil is being placed on its own for configuring the
internal friction angle or soil is being tested with construction material present to
determine the interface friction angle.
The amount of soil weight, which was calculated with regards to what void
ratio is being used for the test (as it was shown in table 4 in section 3.1) can be
poured into the bottom of the shear box.
As the tests were recorded for two separate void ratio, the manner of which
the soil is being put into the box changes. As of the dense packing sample to be test
after pouring the soil and ensuring it has filled in almost all the gaps in the corner and
edges of the box the by using a compactor.
The compactor is placed on top of the soil and it should be pressed against
the soil to attain the densest state.
On the other hand, for the loose state of the specimen, the soil is being
poured into the box from a small height above the box to make a condition for the
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loose state and following this, the box can be shaken with a gentle manner for the
soil to fill the unnatural gaps inside the box.
3. As the soil is dry, it does not require any porous stone or such to be placed
in the box. Once completed the lid of the box can be placed on the top, which is used
to make the normal stress apply at the very centre of the box, which then distributes
the load uniformly then putting the support bolts back in and tighten, as it can be
seen in the figure 11.
Figure 11: Assembly of direct shear apparatus.
4. Take the box to the direct shear machine, then place the piston on top of
the lid, which is connected to the lever, which is used to for the load to be put on and
transferred to the sample as a normal vertical stress, then unscrew the bolts and
take them out.
5. Once everything is in order, then the gauges for vertical and horizontal
movement as well should be set to zero in order to obtain the displacements, before
the test begins. As it is shown in the figure 12 below.
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Figure 12: Reading gauges set to zero and ready for test to begin.
6. After preparing everything, turn on the machine and set the appropriate
shearing rate, in this case 1mm/min, and as of the readings for these test, the
vertical dial gauge and load dial gauge were being recorded for every 0.2mm of
horizontal movement, in order to obtain the vertical movement and the shear
strength respectively.
Figure 13: Shearing rate set to 1mm/min.
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7. The normal loads applied for these tests were, 50kpa, 100kpa and 200kpa.
8. As the tests start to run, the shear stress increase quite rapidly dependant
on the normal stress applied. The shear stress start to rise and as it gets close to the
peak, it starts to fall towards the constant state or flattens, the test should not be
stopped right after the maximum shear stress is attained as it make a massive error
towards the final result, as the apparatus is operated without a computer and the
readings are being recorded by hand, each test needs to be let go until the end.
9. Once completed the rest of the tests for the specimen can be carried out at
different normal load, which then by inputting all the figures, a Coulomb line, shear
stress versus horizontal displacement and vertical movement versus horizontal
displacement can be drawn to establish and illustrate the behaviour of the sample.
As it can be seen in figures 14 and 15 for instance, for the dense state of aggregates
itself with 50kpa as a normal stress.
Figure14: shear stress versus horizontal displacement.
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
50 KPa
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Figure 15: vertical movement versus horizontal displacement.
Simple calculation which was used with regards to the direct shear box:
𝛾 = 𝜌 𝑥 𝑔
𝑒 = 𝐺𝑠 𝑥 𝛾𝑤
𝛾𝑑− 1
Note: 𝛾 (Unit weight of the soil) = 𝛾𝑑 as the specimen is dry.
g = Gravitation (9.81m/s2)
γw = Unit weight of water
Calculate:
Horizontal displacement: by multiplying the dial reading by 0.01mm.
Vertical movement: by multiplying the dial gauge reading by 0.002mm
y = 0.1549x - 0.4177
-1
-0.5
0
0.5
1
1.5
2
0 2 4 6 8 10 12
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
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Shear stress: by (multiplying the load dial reading by the specific gravity) dividing by
[(shearing area [100mm2] x 106)/103].
4. Discussion of Results
This paper will mostly focus on how the factors such as density and surface
roughness of construction material, with three normal loads applied (50kpa, 100kpa
and 200kpa) has an effect on shear strength of the soil.
In addition, all the graphs and charts in the discussion will concentrate on
these factors pertinent to the change in shear strength of the soil and the interface
frictional resistance.
The tests in which the soil was subjected to the mentioned normal stresses,
were conducted with two different void ratios 0.5 and 0.8. Moreover, four different
materials (which have different surface roughness) were considered:
1. Soil/Soil
2. Soil/1 Steel Mesh
3. Soil/2 Steel Mesh
4. Soil/3 Steel Mesh
Hence, by manipulating the depths of steel meshes, different rate of
roughness for the surfaces were achieved.
The system in which the discussion of results will be presented, is to look into
the effect on shear stress-displacement curve for different normal stresses and
different void ratios for the same construction material first and then for different
construction materials, with the main purpose of comparison.
All the factors affecting the shear strength and frictional resistance will be
compared together, so it could be found out which version has the most and closest
strength and resistance similar to of a soil itself. This study shows how the frictional
resistance varies with different depths of steel mesh, which will illustrate how it
affects the shear resistance of the soil.
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4.1. Constant void ratio vs variable normal stress
The results of tests shown below, illustrate characteristics of shear stress-
displacement relationship under dry conditions at same void ratios:
Which clearly show by increasing the normal stress the shear stress hence
increases.
a. Soil/Soil
Figure 16 and figure 17 clearly show the effect of different normal stresses on
the shear strength of the soil, which demonstrate the typical behaviour of soil under
dry conditions and at the void ratios of 0.5 and 0.8 respectively
Figure 16: Shear stress versus horizontal displacement for void ratio of 0.5 for
soil/soil interface.
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/S 50Kpa S/S 100Kpa S/S 200Kpa
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Figure 17: Shear stress versus horizontal displacement for void ratio of 0.8 for soil/soil interface.
b. Soil/1 Steel Mesh
Figure 18, shows the shear stress fluctuation as the horizontal displacement
increases in the densest state and figure 19 illustrates the same behaviour for which
used a void ratio of 0.8, and both of these curves were obtained under dry
conditions.
Figure 18: Shear stress versus horizontal displacement for void ratio of 0.5 for soil/1
steel mesh interface.
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/S 50Kpa S/S 100Kpa S/S 200Kpa
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM1 50 Kpa S/SM1 100 Kpa S/SM1 200 Kpa
23 | P a g e
Figure 19: Shear stress versus horizontal displacement for void ratio of 0.8 for soil/1
steel mesh interface.
c. Soil/2 Steel Mesh
Figure 20 and 21 demonstrate the shear stress versus horizontal
displacement and how it is affected as the normal stress increases, for samples
compacted at 0.5 and 0.8 void ratio respectively.
Figure 20: Shear stress versus horizontal displacement for void ratio of 0.5 for soil/2
steel mesh interface.
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM1 50 Kpa S/SM1 100 Kpa S/SM1 200 Kpa
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM2 50 Kpa S/SM2 100 Kpa S/SM2 200 Kpa
24 | P a g e
Figure 21: Shear stress versus horizontal displacement for void ratio of 0.8 for soil/2
steel mesh interface.
d. Soil/3 Steel Mesh
Figure 22 and 23 illustrate similar behaviour as the other three construction
materials, which is by increasing the normal stress, the shear stress also increases
for the void ratios of 0.5 and 0.8 respectively. As all of these tests established a
similar trend, the relationship can be explained through using the coulomb failure
equation:
Where:
τ = shear stress
c = cohesion of soil which is zero for cohesion-less soils such as sand
σ = Normal stress
ϕ = internal friction angle
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM2 50 Kpa S/SM2 100 Kpa S/SM2 200 Kpa
25 | P a g e
Which by considering the coulomb failure equation, in order to calculate the
internal friction angle and/or interface friction angle, the equation can be rearranged
as follows:
ϕ = tan-1(τ/ σ)
Figure 22: Shear stress versus horizontal displacement for void ratio of 0.5 for soil/3
steel mesh interface.
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM3 50 Kpa S/SM3 100 Kpa S/SM3 200 Kpa
26 | P a g e
Figure 23: Shear stress versus horizontal displacement for void ratio of 0.8 for soil/3
steel mesh interface.
As discussed in this section, by looking into the state where normal stresses
were variable with constant void ratio, it could be concluded what happens to the soil
if the density is constant; and it was proven that by increasing the normal stress,
ideally the shear strength of the soil should in fact rise, which it was clearly shown by
various graphs in this section, through using different versions of steel mesh
interfacing with the soil.
4.2. Constant normal stress vs variable void ratio
Following that, in order to distinguish the effect of void ratio on shear strength
and prove that by changing the density of the soil itself within the tests carried out,
the shear resistance of the soil can in fact be manipulated and produce a higher
frictional resistance.
Hence, with the intention of illustrating that, number of tests were performed
to show that by keeping the normal stresses constant and changing the void ratios
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM3 50 Kpa S/SM3 100 Kpa S/SM3 200 Kpa
27 | P a g e
and by looking at the result it can be concluded that almost often by decreasing the
void ratio, the frictional resistance of the soil does in fact increase; considering the
depth of the steel mesh as well as the normal stress applied to the specimen; as little
as it can be.
The following figures of 24 – 35 show the behaviour of the soil at which, it is
subjected to the constant rate of normal stress in each graph ranging from 50kpa,
100kpa and 200kpa, with variable void ratios of 0.5 (dense) and 0.8 (loose) to show
the effect of density on the shear stress. These tests have been carried out for the
soil/soil, soil/1 steel mesh, soil/2 steel mesh and soil/3 steel mesh.
Finally, individual graphs for the shear stress versus the horizontal
displacement will be provided in the appendices for more details.
Figure 24: Shear stress versus horizontal displacement.
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/S 50Kpa (Dense) S/S 50Kpa (Loose)
28 | P a g e
. Figure 26: Shear stress versus horizontal displacement.
Figure 27: Shear stress versus horizontal displacement.
0
20
40
60
80
100
120
140
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/S 100Kpa (Dense) S/S 100Kpa (Loose)
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/S 200Kpa (Dense) S/S 200Kpa (Loose)
29 | P a g e
Figure 28: Shear stress versus horizontal displacement.
Figure 29: Shear stress versus horizontal displacement.
Figure 30: Shear stress versus horizontal displacement.
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/S 200Kpa (Dense) S/S 200Kpa (Loose)
0
20
40
60
80
100
120
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM1 100 Kpa (Dense) S/SM1 100 Kpa (Loose)
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss
Kn
/m2
Horizontal displacement (mm)
S/SM1 200 Kpa (Dense) S/SM1 200 Kpa (Loose)
30 | P a g e
Figure 31: Shear stress versus horizontal displacement.
Figure 32: Shear stress versus horizontal displacement.
Figure 33: Shear stress versus horizontal displacement.
0
10
20
30
40
50
60
70
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM2 50 Kpa (Dense) S/SM2 50 Kpa (Loose)
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60 70
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM2 100 Kpa (Dense) S/SM2 100 Kpa (Loose)
0
50
100
150
200
250
0 10 20 30 40 50 60 70
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM2 200 Kpa (Dense) S/SM2 200 Kpa (Loose)
31 | P a g e
Figure 34: Shear stress versus horizontal displacement.
Figure 35: Shear stress versus horizontal displacement.
Figure 36: Shear stress versus horizontal displacement.
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM3 50 Kpa (Dense) S/SM3 50 Kpa (Loose)
0
20
40
60
80
100
120
140
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/SM3 100 Kpa (Dense) S/SM3 100 Kpa (Loose)
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss
Kn
/m2
Horizontal displacement (mm)
S/SM3 200 Kpa (Dense) S/SM3 200 Kpa (Loose)
32 | P a g e
4.3. Shear failure envelope
In this study the shear failure envelopes were prepared with regards to
constant void ratios, from which by varying the normal stresses and by plotting them
on the graph, a comparison was concluded to illustrate the difference between a
different version of soil/steel-mesh tests and soil/soil, where through these tests,
different values of internal and interface friction angles were obtained.
Therefore, purely for comparison of such behaviour, the following graphs have
been provided to illustrate under which condition of soil/material interface; the soil
produces a higher value for the angle of friction and hence a higher shear strength,
these were categorised in two major graph for 0.5 and 0.8 void ratios.
Having said that, for more detail, a separate graph for each test will be
provided in the appendices.
Figure 37: Typical shear envelope for soil sample for different interfaces with a void
ratio of 0.5.
0
50
100
150
200
250
0 50 100 150 200 250
Shea
r st
ress
Kn
/m2
Normal stress (Kpa)
Soil/Soile=0.5
Soil/SM1e=0.5
Soil/SM2e=0.5
Soil/SM3e=0.5
Linear(Soil/Soile=0.5)Linear(Soil/SM1e=0.5)Linear(Soil/SM2e=0.5)Linear(Soil/SM3e=0.5)
33 | P a g e
Figure 38: Typical shear envelope for soil sample for different interfaces with a void
ratio of 0.8.
As it can be clearly seen, as the void ratio decreases the critical interface
friction angle increases. By examining more in detail it can be seen that, as void ratio
increases, the interface friction angle between soil with three steel meshes and the
aggregates start to show a higher value than the internal friction angle of the soil
itself, whereas in dense state this phenomena is not true and the internal friction
angle still has a highest value.
These tests suggest that by having a loose state of the soil and increasing the
depth of the steel meshes, it does in fact assist the failure line to be pushed into the
soil to generate a higher value for interface friction and angle and hence a higher
frictional and shear resistance.
Also curves for shear stress ratios versus normal stress were prepared for
each interface test, with different void ratios in order to display how the shear stress
ratios are affected by considering different void ratios. The graphs 39 – 42, hence
visualised this behaviour, for every material interface test with the soil.
0
50
100
150
200
250
0 50 100 150 200 250
Shea
r st
ress
Kn
/m2
Normal stress (Kpa)
Soil/Soile=0.8
Soil/SM1e=0.8
Soil/SM2e=0.8
Soil/SM3e=0.8
Linear(Soil/Soile=0.8)Linear(Soil/SM1e=0.8)Linear(Soil/SM2e=0.8)Linear(Soil/SM3e=0.8)
34 | P a g e
Figure 39: shear stress ratio versus normal stress for soil/soil with different void
ratios.
Figure 40: shear stress ratio versus normal stress for soil/1-steel-mesh with different
void ratios.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 50 100 150 200 250
τ /σ
normal stress (kpa)
Soil/Soil e=0.5
Soil/Soil e=0.8
Linear(Soil/Soile=0.5)
Linear(Soil/Soile=0.8)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 50 100 150 200 250
τ /σ
normal stress (kpa)
Soil/SM1 e=0.5
Soil/SM1 e=0.8
Linear(Soil/SM1e=0.5)
Linear(Soil/SM1e=0.8)
35 | P a g e
Figure 41: shear stress ratio versus normal stress for soil/2-steel-mesh with different
void ratios.
Figure 42: shear stress ratio versus normal stress for soil/3-steel-mesh with different
void ratios.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 50 100 150 200 250
τ /σ
normal stress (kpa)
Soil/SM2 e=0.5
Soil/SM2 e=0.8
Linear(Soil/SM2e=0.5)
Linear(Soil/SM2e=0.8)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 50 100 150 200 250
τ /σ
normal stress (kpa)
Soil/SM3 e=0.5
Soil/SM3 e=0.8
Linear (Soil/SM3e=0.5)
Linear (Soil/SM3e=0.8)
36 | P a g e
As it can be demonstrated, these graphs show how the shear stress ratio
drops as the normal stress increases. Although it has been evidently proven that the
soil/soil interface has higher value of the ratio compared with other interfaces,
however, soil/3-steel-meshes does corresponds to such behaviour in similar manner
as the soil/soil and has the closest value to the soil shear stress ratios.
All other charts prepared for the relations for shear envelopes for individual
soil/material interfaces are provided in the appendices. It is noticed that all the
results produce a rather similar trends.
4.4. Dilatency of tested granular material
As it was mentioned the packing and initial density of soil has a massive
influence on how the soil behaves whilst shearing, hence by considering the granular
material that has been used in this study, an increase in volume can be observed.
For dense and slightly dense packing coarse soil; the soil undergoes grains
contracting at the start of shearing as the normal stress compacts the soil initially, as
this occurs, there will be a point where the interlocking of granular particles will
prevent further contraction and since there will be no more shearing due to this,
therefore, the soil has to dilate (expand in volume) in order to roll/slide pass one
another and shear.
As additional shear force is required to dilate the soil, peak strength occurs.
Once the peak is reached and has been overcome by continued shearing, the soil
reaches a state where the applied shear reduces and there will be no further
changes in volume of the soil, this is called strain softening.
In this section to show this behaviour of soil, the soil was subjected to a
number of different normal stress with different void ratios of 0.5 and 0.8, for different
interfaces to assess the performance of the soil.
The graphs 43 – 50, show the volume change of the soil subjected to 50kpa,
100kpa and 200 kpa for each soil/material interfaces with different packings.
37 | P a g e
Figure 43: Vertical movement and horizontal displacement curve for soil/soil with
void ratio of 0.5.
Figure 44: Vertical movement and horizontal displacement curve for soil/1-steel-
mesh with void ratio of 0.5.
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
S/S 50Kpa S/S 100Kpa S/S 200Kpa
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
S/SM1 50 Kpa S/SM1 100 Kpa S/SM1 200 Kpa
38 | P a g e
Figure 45: Vertical movement and horizontal displacement curve for soil/2-steel-
mesh with void ratio of 0.5.
Figure 46: Vertical movement and horizontal displacement curve for soil/3-steel-
mesh with void ratio of 0.5.
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
S/SM2 50 Kpa S/SM2 100 Kpa S/SM2 200 Kpa
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
S/SM3 50 Kpa S/SM3 100 Kpa S/SM3 200 Kpa
39 | P a g e
Figure 47: Vertical movement and horizontal displacement curve for soil/soil with
void ratio of 0.8.
Figure 48: Vertical movement and horizontal displacement curve for soil/1-steel-
mesh with void ratio of 0.8.
-0.5
0
0.5
1
1.5
2
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
S/S 50Kpa S/S 100Kpa S/S 200Kpa
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
S/SM1 50 Kpa S/SM1 100 Kpa S/SM1 200 Kpa
40 | P a g e
Figure 49: Vertical movement and horizontal displacement curve for soil/2-steel-
mesh with void ratio of 0.8.
Figure 50: Vertical movement and horizontal displacement curve for soil/3-steel-
mesh with void ratio of 0.8.
-0.1
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
S/SM2 50 Kpa S/SM2 100 Kpa S/SM2 200 Kpa
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
S/SM3 50 Kpa S/SM3 100 Kpa S/SM3 200 Kpa
41 | P a g e
As it can be undoubtedly seen the recorded results of the tests, suggest that
by increasing the normal stress and the load applied to the soil the volume change
and dilation of the soil decreases.
All the other charts which present the results for each individual test carried
out for all the soil/material interfaces will be accessible in the appendices for more
details.
Considering the results and that through shearing the soil in the shear box, the lid
moves upwards at an angle of dilation (ψ), therefore, in order to calculate the dilation
angle of each soil the following method was carried out:
Ψ = tan-1 (-dεv/dγ)
Which was obtained by using the trend-line for each test and each normal
stress to produce the exact dilation angle.
Since the dilation of the soil, has an impact on the friction and shearing
resistance, then the actual shearing resistance mobilised will be ϕ’current which is
made up of two component:
ϕ’current = ϕ’crit + ψ
However, Bolton (1986), showed that in plane strain, the contribution of
dilation is better represented by:
ϕ’current = ϕ’crit + 0.8ψ
This correction to the ϕ’current, will decrease the value to the critical state value ϕ’crit.
Tables 6 – 13 present the values for the initial internal and interface friction angles as
well as the dilation angles, hence, the altered internal and interface friction angles for
each soil/material interfaces and normal stress for different void ratios.
42 | P a g e
Soil/Soil
e = 0.5
Normal stress
(σ) (kpa)
Shear stress
(τ) (kpa) ϕ’crit (ᵒ) 0.8ψ (ᵒ) ϕ’current (ᵒ)
50 62 51.11 5.29 56.4
100 121.75 50.6 7.1 57.7
200 216.54 47.27 5 52.27
Table 6: Interface friction angle for soil/soil with e = 0.5.
Soil/Soil
e = 0.8
Normal stress
(σ) (kpa)
Shear stress
(τ) (kpa) ϕ’crit (ᵒ) 0.8ψ (ᵒ) ϕ’current (ᵒ)
50 73.96 55.94 7.45 63.4
100 110.3 47.8 4.8 52.6
200 206.4 45.9 3.97 49.87
Table 7: Interface friction angle for soil/soil with e = 0.8.
43 | P a g e
Soil/1 Steel Mesh
e = 0.5
Normal stress
(σ) (kpa)
Shear stress
(τ) (kpa) ϕ’crit (ᵒ) 0.8ψ (ᵒ) ϕ’current (ᵒ)
50 60 50.2 6.88 57.08
100 111 47.98 5.78 53.76
200 200.5 45.1 4.48 49.58
Table 8: Interface friction angle for soil/1 steel mesh with e = 0.5.
Soil/1 Steel Mesh
e = 0.8
Normal stress
(σ) (kpa)
Shear stress
(τ) (kpa) ϕ’crit (ᵒ) 0.8ψ (ᵒ) ϕ’current (ᵒ)
50 63.5 51.78 3.62 55.4
100 113.7 48.67 1.57 50.24
200 199.5 44.93 1.76 46.69
Table 9: Interface friction angle for soil/1 steel mesh with e = 0.8.
44 | P a g e
Soil/2 Steel Mesh
e = 0.5
Normal stress
(σ) (kpa)
Shear stress
(τ) (kpa) ϕ’crit (ᵒ) 0.8ψ (ᵒ) ϕ’current (ᵒ)
50 60.3 50.33 5.92 56.25
100 120.2 50.24 5.16 55.4
200 203.45 45.5 4.24 49.74
Table 10: Interface friction angle for soil/2 steel mesh with e = 0.5.
Soil/2 Steel Mesh
e = 0.8
Normal stress
(σ) (kpa)
Shear stress
(τ) (kpa) ϕ’crit (ᵒ) 0.8ψ (ᵒ) ϕ’current (ᵒ)
50 60 50.2 2.11 52.31
100 103.6 46.01 1.98 47.99
200 201 45.14 1.93 47.07
Table 11: Interface friction angle for soil/2 steel mesh with e = 0.8.
45 | P a g e
Soil/3 Steel Mesh
e = 0.5
Normal stress
(σ) (kpa)
Shear stress
(τ) (kpa) ϕ’crit (ᵒ) 0.8ψ (ᵒ) ϕ’current (ᵒ)
50 59.8 50.1 5.96 56.01
100 127.9 51.98 4.86 56.84
200 205.3 45.75 3.2 48.95
Table 12: Interface friction angle for soil/3 steel mesh with e = 0.5.
Soil/3 Steel Mesh
e = 0.8
Normal stress
(σ) (kpa)
Shear stress
(τ) (kpa) ϕ’crit (ᵒ) 0.8ψ (ᵒ) ϕ’current (ᵒ)
50 68.62 53.92 4.08 58
100 123.62 51.03 2.28 53.31
200 208.5 46.2 1.84 48.04
Table 13: Interface friction angle for soil/3 steel mesh with e = 0.8.
46 | P a g e
4.5. Void ratio (e) and friction angle (ϕ)
As mentioned previously, the internal and interface friction angle increase as the
void ratio decreases. In this section the average values of friction angles for all
materials will be compared.
Figure 51 shows the typical relation between the friction angle and void ratio
and it can be observed that while void ratio increases, the friction angle drops. This
can be evidently demonstrated by the slope for the soil/soil interaction as has a
higher slope, hence drop.
Figure 51: Relationship between void ratio and friction angle for all soil/material
interfaces under dry conditions.
It should be noted that the interface friction angle for soil interfaced with three steel
meshes does not change significantly with the change of void ratio.
44
44.5
45
45.5
46
46.5
47
47.5
0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85
Fric
tio
n A
ngl
e (ᵒ
)
Void Ratio (e)Soil/Soil Soil/SM1 Soil/SM2 Soil/SM3
Linear (Soil/Soil) Linear (Soil/SM1) Linear (Soil/SM2) Linear (Soil/SM3)
47 | P a g e
It is noticed from all the curves that the relation is rather linear and as the void
ratio increases the friction angle decrease.
Therefore, table 14 presents the average values of friction angle for all
material with all normal stresses combined and considered, for different void ratios
(0.5 and 0.8).
Interfaces Void ratio (e) Friction angle
(ϕ) (ᵒ)
Soil/Soil 0.5 47.1
0.8 44.9
Soil/1-steel-mesh 0.5 44.8
0.8 44.5
Soil/2-steel-mesh 0.5 45.3
0.8 44.7
Soil/3-steel-mesh 0.5 45.85
0.8 45.72
Table 14: Overall friction angle for soil/material interfaces, with different void ratios.
48 | P a g e
5. Conclusion
Direct shear tests were conducted in order to illustrate the effect of surface
roughness of construction material; which in this study steel meshes with variety of
depths were used; on the shear strength of the soil, also the effect that different void
ratios and densities have on this matter.
The soil used was construction aggregates with grain sizes of 2mm used to carry out
the tests. To determine the shear stress and hence the angle of friction, whether
internal or interface, direct shear box apparatus was used, with normal stresses of
50kpa, 100kpa and 200kpa on dry conditions.
The materials used to evaluate the interface friction angle were steel meshes that
were prepared with depths of 2mm, 4mm and 6mm which was made available by
welding the steel meshes together.
Through carrying out these test, the study here draw the following conclusions:
From shear stress and horizontal displacement graphs considering constant
void ratio and variable normal stresses, it was understood that as the normal
stress increases, shear stresses increase.
However by rearranging the graphs by considering constant normal stresses
and variable void ratios, it could be observed that shear stress increases as
the void ratios decrease (density increases), hence the density has a massive
impact on shear stress and frictional resistance manipulation.
From the shear envelopes, it was noticed that by decreasing the friction angle
(although it fluctuates from time to time) the shear stress increases.
The shear strength of soil is always higher compared to the interface friction
angle between the soil and construction material.
Future work can be carried out, to evaluate and observe the behaviour of the soil by
adding up to the depth of the steel meshes and see what sort of differentiation they
make to the shear strength and frictional resistance of the soil, also considering the
change of moisture contents, grain sizes and angularity to evaluate how these have
an effect on the shear strength of the soil.
49 | P a g e
6. Appendices
A. Relationship between the shear stress and the horizontal displacement for all
soil/material interactions with e = 0.5 as well as a graph for the comparison of
all curves with similar void ratio.
B. Relationship between the shear stress and the horizontal displacement for all
soil/material interactions with e = 0.8 as well as a graph for the comparison of
all curves with similar void ratio.
C. Graphs to show the comparison of all relationships between the shear stress
and the horizontal displacement for all soil/material interactions with similar
normal stress and variable void ratios.
D. Relationship between the vertical movement and the horizontal displacement
for all soil/material interactions with e = 0.5 as well as a graph for the
comparison of all.
E. Relationship between the vertical movement and the horizontal displacement
for all soil/material interactions with e = 0.8 as well as a graph for the
comparison of all.
F. Coulomb failure envelopes for all soil/material interactions with e = 0.5.
G. Coulomb failure envelopes for all soil/material interactions with e = 0.8.
50 | P a g e
A. Relationship between the shear stress and the horizontal displacement for all
soil/material interactions with e = 0.5 as well as a graph for the comparison of
all curves with similar void ratio.
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/soil,50 Kpa,e=0.5
-20
0
20
40
60
80
100
120
140
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/soil, 100 Kpa, e=0.5
-50
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/soil, 200 Kpa, e=0.5
51 | P a g e
-10
0
10
20
30
40
50
60
70
0 2 4 6 8 10 12
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM1, 50 Kpa, e=0.5
-20
0
20
40
60
80
100
120
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM1, 100 Kpa, e=0.5
-50
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM1, 200 Kpa, e=0.5
52 | P a g e
-10
0
10
20
30
40
50
60
70
0 2 4 6 8 10 12
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM2, 50 Kpa, e=0.5
-20
0
20
40
60
80
100
120
140
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM2, 100 Kpa, e=0.5
-50
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM2, 200 Kpa, e=0.5
53 | P a g e
-10
0
10
20
30
40
50
60
70
0 2 4 6 8 10 12
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM3, 50 Kpa, e=0.5
-20
0
20
40
60
80
100
120
140
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM3, 100 Kpa, e=0.5
-50
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM3, 200 Kpa, e=0.5
54 | P a g e
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement
S/S 50Kpa S/S 100Kpa
S/S 200Kpa S/SM1 50 Kpa
S/SM1 100 Kpa S/SM1 200 Kpa
S/SM2 50 Kpa S/SM2 100 Kpa
S/SM2 200 Kpa S/SM3 50 Kpa
S/SM3 100 Kpa S/SM3 200 Kpa
55 | P a g e
B. Relationship between the shear stress and the horizontal displacement for all
soil/material interactions with e = 0.8 as well as a graph for the comparison of
all curves with similar void ratio.
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/Soil, 50 Kpa, e=0.8
0
20
40
60
80
100
120
0 5 10 15
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/Soil, 100 Kpa, e=0.8
56 | P a g e
-50
0
50
100
150
200
250
0 5 10 15
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/Soil, 200 Kpa, e=0.8
-10
0
10
20
30
40
50
60
70
0 2 4 6 8 10 12
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM1, 50 Kpa, e=0.8
-20
0
20
40
60
80
100
120
0 5 10 15
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM1, 100 Kpa, e=0.8
57 | P a g e
-50
0
50
100
150
200
250
0 5 10 15
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM1, 200 Kpa, e=0.8
-10
0
10
20
30
40
50
60
70
0 2 4 6 8 10 12
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM2, 50 Kpa, e=0.8
-20
0
20
40
60
80
100
120
0 5 10 15
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM2, 100 Kpa, e=0.8
58 | P a g e
-50
0
50
100
150
200
250
0 5 10 15
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM2, 200 Kpa, e=0.8
-10
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM3, 50 Kpa, e=0.8
-20
0
20
40
60
80
100
120
140
0 5 10 15
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM3, 100 Kpa, e=0.8
59 | P a g e
-50
0
50
100
150
200
250
0 5 10 15
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
Soil/SM3, 200 Kpa, e=0.8
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)S/S 50Kpa S/S 100Kpa S/S 200Kpa
S/SM1 50 Kpa S/SM1 100 Kpa S/SM1 200 Kpa
S/SM2 50 Kpa S/SM2 100 Kpa S/SM2 200 Kpa
S/SM3 50 Kpa S/SM3 100 Kpa S/SM3 200 Kpa
60 | P a g e
C. Graphs to show the comparison of all relationships between the shear stress
and the horizontal displacement for all soil/material interactions with similar
normal stress and variable void ratios.
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/S 50Kpa (Dense) S/S 50Kpa (Loose)
S/SM1 50 Kpa (Dense) S/SM1 50 Kpa (Loose)
S/SM2 50 Kpa (Dense) S/SM2 50 Kpa (Loose)
S/SM3 50 Kpa (Dense) S/SM3 50 Kpa (Loose)
61 | P a g e
0
20
40
60
80
100
120
140
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/S 100Kpa (Dense) S/S 100Kpa (Loose)
S/SM1 100 Kpa (Dense) S/SM1 100 Kpa (Loose)
S/SM2 100 Kpa (Dense) S/SM2 100 Kpa (Loose)
S/SM3 100 Kpa (Dense) S/SM3 100 Kpa (Loose)
62 | P a g e
0
50
100
150
200
250
0 2 4 6 8 10 12 14
She
ar s
tre
ss K
n/m
2
Horizontal displacement (mm)
S/S 200Kpa (Dense) S/S 200Kpa (Loose)
S/SM1 200 Kpa (Dense) S/SM1 200 Kpa (Loose)
S/SM2 200 Kpa (Dense) S/SM2 200 Kpa (Loose)
S/SM3 200 Kpa (Dense) S/SM3 200 Kpa (Loose)
63 | P a g e
D. Relationship between the vertical movement and the horizontal displacement
for all soil/material interactions with e = 0.5 as well as a graph for the
comparison of all.
Soil/soil e = 0.5 50kpa
Soil/soil e = 0.5 100kpa
y = 0.1549x - 0.4177
-1
-0.5
0
0.5
1
1.5
2
0 2 4 6 8 10 12Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.1559x - 0.4217
-1
-0.5
0
0.5
1
1.5
2
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
64 | P a g e
Soil/soil e = 0.5 200kpa
Soil/1-Steel-mesh e = 0.5 50kpa
y = 0.1092x - 0.3371
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.1551x - 0.2296
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 2 4 6 8 10 12
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
65 | P a g e
Soil/1-Steel-mesh e = 0.5 100kpa
Soil/1-Steel-mesh e = 0.5 200kpa
y = 0.1268x - 0.32
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.0981x - 0.2878
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
66 | P a g e
Soil/2-Steel-mesh e = 0.5 50kpa
Soil/2-Steel-mesh e = 0.5 100kpa
y = 0.13x - 0.2328
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.1286x - 0.2275
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
67 | P a g e
Soil/2-Steel-mesh e = 0.5 200kpa
Soil/3-Steel-mesh e = 0.5 50kpa
y = 0.0923x - 0.205
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.1307x - 0.2129
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
68 | P a g e
Soil/3-Steel-mesh e = 0.5 100kpa
Soil/3-Steel-mesh e = 0.5 200kpa
y = 0.1287x - 0.2054
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.0688x - 0.1574
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
69 | P a g e
E. Relationship between the vertical movement and the horizontal displacement
for all soil/material interactions with e = 0.8 as well as a graph for the
comparison of all.
Soil/soil e = 0.8 50kpa
Soil/soil e = 0.8 100kpa
y = 0.164x - 0.3673
-0.5
0
0.5
1
1.5
2
0 2 4 6 8 10 12
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.1053x - 0.2799
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
70 | P a g e
Soil/soil e = 0.8 200kpa
Soil/1-Steel-mesh e = 0.8 50kpa
y = 0.0867x - 0.2952
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.079x - 0.195
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 2 4 6 8 10 12
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
71 | P a g e
Soil/1-Steel-mesh e = 0.8 100kpa
Soil/1-Steel-mesh e = 0.8 200kpa
y = 0.0342x - 0.1583
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.0384x - 0.2143
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
72 | P a g e
Soil/2-Steel-mesh e = 0.8 50kpa
Soil/2-Steel-mesh e = 0.8 100kpa
y = 0.13x - 0.2328
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.1286x - 0.2275
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
73 | P a g e
Soil/2-Steel-mesh e = 0.8 200kpa
Soil/3-Steel-mesh e = 0.8 50kpa
y = 0.0923x - 0.205
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.0886x - 0.1836
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10 12
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
74 | P a g e
Soil/3-Steel-mesh e = 0.8 100kpa
Soil/3-Steel-mesh e = 0.8 200kpa
y = 0.0498x - 0.1242
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
y = 0.04x - 0.2288
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0 2 4 6 8 10 12 14
Ve
rtic
al m
ove
me
nt
(mm
)
Horizontal displacement (mm)
75 | P a g e
F. Coulomb failure envelopes for all soil/material interactions with e = 0.5.
Soil/Soil e = 0.5
Soil/1-Steel-mesh e = 0.5
y = 1.0769x + 5.842
0
50
100
150
200
250
0 50 100 150 200 250
She
ar s
tre
ss a
t fa
ilure
(kN
/m2
)
Normal stress (kN/m2)
Coulumb envelope
e=0.5
Linear (e=0.5)
y = 0.9917x + 6.1
0
50
100
150
200
250
0 50 100 150 200 250
She
ar s
tre
ss a
t fa
ilure
(kN
/m2
)
Normal stress (kN/m2)
Coulumb envelope
e=0.5
Linear (e=0.5)
76 | P a g e
Soil/2-Steel-mesh e = 0.5
Soil/3-Steel-mesh e = 0.5
y = 1.0116x + 7.47
0
50
100
150
200
250
0 50 100 150 200 250
She
ar s
tre
ss a
t fa
ilure
(kN
/m2
)
Normal stress (kN/m2)
Coulumb envelope
e=0.5
Linear (e=0.5)
y = 1.0264x + 8.44
0
50
100
150
200
250
0 50 100 150 200 250
She
ar s
tre
ss a
t fa
ilure
(kN
/m2
)
Normal stress (kN/m2)
Coulumb envelope
e=0.5
Linear (e=0.5)
77 | P a g e
G. Coulomb failure envelopes for all soil/material interactions with e = 0.8.
Soil/Soil e = 0.8
Soil/1-Steel-mesh e = 0.8
y = 0.9977x + 10.364
0
50
100
150
200
250
0 50 100 150 200 250
She
ar s
tre
ss a
t fa
ilure
(kN
/m2
)
Normal stress (kN/m2)
Coulumb envelope
e=0.8
Linear (e=0.8)
y = 0.9821x + 8.24
0
50
100
150
200
250
0 50 100 150 200 250
She
ar s
tre
ss a
t fa
ilure
(kN
/m2
)
Normal stress (kN/m2)
Coulumb envelope
e=0.8
Linear (e=0.8)
78 | P a g e
Soil/2-Steel-mesh e = 0.8
Soil/3-Steel-mesh e = 0.8
y = 0.9901x + 4.52
0
50
100
150
200
250
0 50 100 150 200 250
She
ar s
tre
ss a
t fa
ilure
(kN
/m2
)
Normal stress (kN/m2)
Coulumb envelope
e=0.8
Linear (e=0.8)
y = 1.0253x + 10.472
0
50
100
150
200
250
0 50 100 150 200 250
She
ar s
tre
ss a
t fa
ilure
(kN
/m2
)
Normal stress (kN/m2)
Coulumb envelope
e=0.8
Linear (e=0.8)
79 | P a g e
7. Reference
Al-Mhaidib, Abdullah I. "Influence of Shearing Rate on Interfacial Friction between
Sand and Steel." Engineering Journal of the University of Qatar 19 (2006): 1-16.
Web.
Bolton, M. D., (1979). “A guide to Soil Mechanics” Macmillan Press Ltd, London.
British Standard, (2004). “Geotehcnical investigation and testing identification and
classification of soil: Part 2: Principles for a classification”, EN ISO 14688-2:2004
Das, Braja M., (1997). “Advanced soil mechanics”, Second Edition, California State
University, Sacramento.
Das, Braja M., (2005), “Fundamental of Geotechnical Engineering”, 4th Edition,
California State University, Sacramento
Forst, J.D. and Han, J., 1999, Behaviour of interfaces between fiber-reinforced
polymers and sands, Journal of geotechnical and geoenviromental engineering,
125:633-640.
Gireesha, T. and K. Muthukkumaran. "Study on Soil Structure Interface Strength
Property." International Journal of Earth Sciences and Engineering 4.6 (2011):
89-93. Web
Laskar, Anowar H. "A Study on Deformation of the Interface between Sand and Steel Plate under Shearing." Proceedings of Indian Geotechnical Conference (2011): 895-898. Web.
Potyondy, J. G., 1961, “Skin Friction between Various Soils and Construction
Materials”. Geotechnique 11.4: 339-353.
Rinne, N.F., 1989, Evaluation of interface friction between cohesionless soil and
common construction materials, the University of British Columbia, Canada.
Uesugi, M. and Kishida, H., 1986, Frictional resistance at yield between dry sand
and mild steel. Soil Foundation.
Yoshimi, Y. and Kishida, T., 1981, Friction between sand and metal surfaces. In:
Proceedings of 10th International Conference on Soil Mechanics and Foundation
Engineering, Stockholm, Sweden, vol. 1.