International Journal of Geosciences, 2010, 44-50
doi:10.4236/ijg.2010.11006 Published Online May 2010 (http://www.SciRP.org/journal/ijg)
Effects of Polypropylene Fibers on the
Shear Strength of Sandy Soil
Mousa F. Attom, Adil K. Al-Tamimi
Civil Engineering Department, College of Engineering, American University of Sharjah, Sharjah, UAE
Received March 1, 2010; revised March 27, 2010; accepted April 20, 2010
Abstract
This paper presents the effect of two types of polypropylene fibers on shear strength parameters of sandy soil.
To achieve the goals of this research, a sandy soil was obtained from a depth of 40 cm from the natural
ground surface around American University of Sharjah. Two types of polypropylene fibers; one highly flexi-
ble with flat profile and the other with relatively high stiffness and crimpled profile were used in this study
with four different aspect ratios (L/D) for each type. The initial physical properties of the sand such as spe-
cific gravity, angle of internal friction and shear strength were obtained in accordance with American Stan-
dard for Testing and Materials (ASTM). The sandy soils were mixed with the two types of fibers at different
percentages by dry weight of the sand and four different aspect ratios. The test results of the study showed
that the shear strength of the sand increased with increasing the flexible flat profile fibers content. Also it
was noticed that by increasing the aspect ratio of the flexible flat profile the angle of internal friction and the
shear strength increased. The crimpled profile fiber increased the shear strength of the sand under high nor-
mal load and has small or no effect on shear strength of the sand at low aspect ratio under low normal load.
Keywords: Sand, Fibers, Angle of Internal Friction, Shear Strength, Aspect Ratio
1. Introduction
Due to the increasing cost of high quality materials
needed for different geotechnical projects, engineers try
to improve the physical properties of local soils through-
out different methods and techniques. The word im-
provement means to increase the shear strength, reducing
settlements, resists harsh environment conditions such as
thawing and freezing, and decreases or eliminates all
problems associated with weak soils. Soil stabilization
could be applied to both sandy and clayey soil through
mechanical and chemical methods. There are many com-
mon methods-mechanical or chemical-found in the lit-
eratures that were used to improve the physical proper-
ties of the soils. [1] showed that the increase of the com-
paction energy effort will increase the shear strength
properties of the clayey soils. [2] used gypsum as an ad-
ditive for stabilization of clay against swelling. He con-
cluded that the gypsum can be used as a stabilizing agent
for expansive clay against swelling effectively. Al-
Rawas et al. [3] indicated that the addition of lime and
cement will reduce both the swell potential and swelling
pressure of expansive clayey soils. [4] used natural re-
sources such as volcanic ash, ground natural lime, ce-
ment and their combination to stabilize soil for construc-
tion application. [5] studied the effect of silica fume on
fine grain soils exposed to freeze and thaw. He found
that the addition silica fume can be successfully used to
reduce the effect of freezing and thawing cycles on
strength and permeability of fine grained soils. In addi-
tion to these methods, other methods also exist such as
wet-dry cycles and thermal methods [6,7].
Recently, engineers started to use different types of
fiber in soil stabilizations. These fibers are found in the
market as short, discrete materials with different aspect
ratio and they can be mixed randomly with the soil, as
cement, lime, or other additives at different percentages.
The main reason of using randomly oriented fibers is to
maintain strength isotropy and the lack of potential weak
planes that may develop parallel to oriented reinforce-
ment [8,9]. Fatani et al. [10] studied the effect of both
aligned and randomly oriented metallic fibers on silty
sand. It was found that mixing fibers with silty sand soil
will increase the peak strength and residual strength
100% and 300% respectively over the untreated soil.
Ziegler et al. [11] studied the effect of short polymeric

M. F. ATTOM ET AL.
45
fibers on crack behavior of clay subjected to drying and
wetting conditions. He concluded that the addition of
fibers to the clay soil is very effective in reducing the
amount of desiccation cracking and increasing the tensile
strength. [12] in his study indicated that the residual
shear strength angle of sand will increase by mixing sand
with discrete fiber. Esna-ashari [13] used cord waste fi-
ber to reinforce the sandy soil. They found that the inclu-
sion of tire cord fiber can change significantly the brittle
behavior of sandy soil to more ductile and also increased
both the peak strength and angle of internal friction of
sand. Gray and Ohashi [14] and Park and Tan [15] used
randomly oriented discrete fibers in their research to re-
inforce sand. Freitag [16] mixed the fiber with clayey
soil and showed that addition of fiber will increase the
strength and ductility than plain clayey soil. The addition
of nylon fiber by Kumar and Tabor [17] resulted in sig-
nificant increase in the residual strength of silty clay soil.
The test by Cai et al. [18] reported that there is a signifi-
cant improvement on the engineering properties of the
fiber-lime treated soil. Due to the encouraging findings
of using discrete fiber with both sandy and clayey soils,
the fibers are used in different construction applications
such as retaining structures, embankments, subgrade and
landfill liners and covers. The main objective of this
study is to investigate the effect of two types of fibers on
some physical properties of sandy soil. The parameters
investigated in this study include shear strength proper-
ties and angle of internal friction at different fiber per-
centages and aspect ratios.
2. Polypropylene Fiber Type A & B
Two types of fibers are used in the research; both fibers
are extruded from a natural Polypropylene homo poly-
mer. The two fibers were given symbols A and B in the
discussion. Type A is formed into a flat profile with high
flexibility where type B formed into a crimped profile
with high relative stiffness in order to anchor it with the
matrix. The combination between the large number of
fibers per kg, its shape and anchoring capability with the
matrix, would provide a toughness and ductility to the
material. Both types have high resistance to acid/alkali
attack and are therefore suitable for use in wet under-
ground conditions. Table 1 shows the physical properties
of the two types of fibers used in this research.
3. Experimental Program
A sandy soil was selected from around American Uni-
versity at Sharjah and brought to soil testing laboratory.
The soils were extracted from 40 cm in depth from origi-
nal ground surface. The initial physical properties of the
sandy soil such as gradation ASTM D-422, specific grav-
ity ASTM D-854, and maximum dry density and opti-
mum water content ASTM D-1557 were determined in
accordance with American Standard for Testing and
Materials (ASTM) standard procedures. Table 2 shows
the initial physical properties of the sandy soil used in
the study. The sandy soil was mixed with the two types
of fibers at different percentages by dry weight of the
sand and different aspect ratios. The percentages of the
fibers are 1%, 2%, 3%, 4%, and dry weight of the sand.
The aspect ratio index of the fibers, which is dimen-
sionless, was used in the analysis instead of the length.
At each percentage, four different aspect ratios (L/D) of
the fibers were used with constant diameter and variable
length. Because of the difference in diameter between
type A and type B fiber four different aspect ratios were
used for each type. The aspect ratios used for type A are
38.5, 77, 115.5 and 154 while the aspect ratio for type B
are 10.4, 20.8, 31.2 and 41.7.
Table 1. Properties of the two types of fibers used in this study.
Characteristics Fiber Fiber
Type A Type B
Fiber Cross section mm² 0.234 0.75
Fiber length 50 mm 40 mm
Diameter 0.13 mm 0.48 mm
Tensile strength at yield (N/mm²) 1004 250
Table 2. Physical prosperities of the sand used in this study.
Physical Properties
Shear Strength
Angle of Internal friction (deg) 19
Cohesion (kPa) 0
Compaction
Maximum dry unit weight (kN/m3) 17.9
Minimum dry unit weight (kN/m3) 14.3
Optimum moisture content (%) 12.8
Grain size distribution
Clay ( ＜ 2 μm) 6
Silt ( 2 μm-75 μm) 18
Sand ( 75 μm-2mm) 76
Effective size D10 (mm) 0.007
D30 (mm) 0.12
D60 (mm) 0.33
Specific gravity of solid, Gs
Gs 2.66

46 M. F. ATTOM ET AL.
Enough number of samples was prepared at 95% rela-
tive compaction and optimum moisture content with dif-
ferent fiber content. Predetermined amount of soil was
obtained and mixed with the two types of fibers sepa-
rately and compacted in the direct shear mold to obtain
the 95% relative compaction. Direct shear test ASTM
D-3080 was conducted on all sample under three normal
loads. (28 kPa, 55 kPa, 110 kPa). The remolded speci-
mens were sheared under a constant strain rate and de-
formations were recorded throughout the experiment. To
obtain the shear strength and the angle of internal friction
of the sand-fiber mixture at each percentage three iden-
tical specimens were prepared and tested under three
different normal loads.
4. Results and Discussion
4.1. The Effect of Fibers on the Shear Strength,
Angle of Internal Friction and Stress-Strain
Relationships of the Sand
Figures 1 and 2 depicts the shear strength behavior and
stress-strain relationships of sandy soil mixed with the
type A and type B fiber respectively at different per-
centages and under normal load equal to 28 kPa. Figure
1 concluded that the increase in the percentages of type
A fiber will result in increasing the shear strength. Fig-
ure 2 showed the increase of type B fiber has a small or
no effect on shear strength up to 3%. The increase in the
percentage of type B fiber more than 3% will result in
decreasing the shear strength. The summary of the effect
of adding both fiber A and fiber B on shear strength of
sand under three normal loads was shown in Figure 3.
This figure was obtained from the stress-strain relation
from the direct shear test under different normal loads
equal to 28 kPa, 55 kPa and 110 kPa and for sand mixed
Strain (%)
0.02.55.07.510.0 12.5 15.0 17.5 20.0
Shear strength (kPa)
0
2
4
6
8
10
12
14
16
0.0
1.0%
2.0%
3.0%
4.0%
Figure 1. The effect of type A fiber on shear strength of
sand under normal load equal to 28 kPa.
Strain (%)
Shear strength (kPa)
Figure 2. The effect of type B fiber on shear strength of
sand under normal load equal to 28 kPa.
Percentages of fiber
Shear strength kN/m
2
Figure 3. The effect of the fibers on the shear strength of
the sand under three different normal loads.
with type A and type B respectively. This figure conclu-
des that the addition of type A fiber will increase the she-
ar strength of the sand under the three normal loads. The
increase in the percentages of nylon fiber from 0.0% to
4% resulted in increasing the shear strength from 9.5 kPa
to 15.1 kPa respectively, under normal load equal to 28 kPa.
The addition of type A fiber up to 4% increased the shear
strength of the sand up to 59%. As the normal load in-
creased the addition of type A resulted in increasing the
shear strength. For example the shear strength of the
sand increased from 39.9 kPa to 66.4 kPa when the type
A fiber increased from 0.0% to 4.0% under normal load
equal to 110 kPa. The percentages in shear strength incr-
eased is about 66.4% under normal load equal to 110 kPa
compares to 59% increased under normal load 28 kPa.
Different findings was noticed when the sand was
mixed with type B fiber. As shown in Figure 4 the addi-
tion of Type B fiber up to 3% by dry weight of the sand

M. F. ATTOM ET AL.
47
has small or no effect on the shear strength at small nor-
mal load (28 kPa). The addition of further fiber will re-
sult in decreasing the shear strength at 28 kPa normal
load. The shear strength decreased from 9.5 kPa at 0.0%
fiber content to 8.8 kPa at 4% fiber content. However,
addition of type B fiber resulted in increasing shear
strength of sand at higher normal load. As shown in Fig-
ure 3 and at 55 kPa and 110 kPa normal loads the incre-
ase in the percentages in the type B fiber resulted in incr-
easing the shear strength of the sand. The shear strength
of sand under normal load equal to 55 kPa increased
from 19.5 kPa and 26 kPa when the percentages of B
fiber increased from 0.0% to 4%. The same behavior was
noticed at higher normal loads. The shear strength in-
creased under normal load 110 kPa from 39.9 kPa at
0.0% fiber content to 63 kPa when the fiber content
reached 4%.
Another conclusion can be drawn from the stress
strain relationship. It was noticed there was no peak be-
havior of sand due to addition of these two fibers. All
specimen with both fiber reached fail without exercising
peak strength.
The effect of adding both types of fibers on the angle
of internal friction of the sand is shown in Table 3. It is
clear in this table that the addition of type A fiber will
increase the angle of internal friction of the sand under
any loading level. The angle of internal friction increased
as much as 49% when the Type A fiber increased by 4%.
Under normal load equal to 28 kPa. As the normal load
increased the angle of internal friction increased to reach
64% under 110 kPa normal load and 4% fiber content.
The effect of type B fiber is also shown in Table 3. The
addition of type B fiber has no effect on the angle of in-
ternal friction under small loading condition. As the
normal load increased the addition of type B fiber will
result in increasing the angle of internal friction. The
angle of internal friction increased as much as 57% under
110 kPa normal load and 4% fiber content. It can be
concluded that the type B fiber has a very small on no
effect on the angle of internal friction under small normal
load and it has a significant effect on the angle of internal
friction at large value of normal loading.
As it was mentioned earlier, the stress-strain relation
curves were obtained from a direct shear test under 28 kPa
normal loads. Figure 1 shows the effect of type A fiber
on the stress stain relation of sand. It is clear from this
curve that as the percentages of type A fiber increased
the strain failure increased too. The failure strain due to
addition type A fiber increased from 8.6% to 10.0% and
11.5% when the fiber percentages increased from 0.0%
to 2% and 4% respectively. This finding may conclude
that the addition of type A fiber will increase the ductil-
ity of the sandy soil which is defined as the strain at fail-
ure of the soil specimen. The increase of the ductility of
the soils with increasing the fiber contents is attributed to
the effect of fibers inclusions in the sandy soil that im-
proved the properties of the soil. Figure 2 shows the
effect of type B fiber on the stress-strain relation of the
sand. It was noticed that adding the type B fiber up to 3%
has insignificant effect on ductility of the sand while
adding the type B fiber more than 3% will result in de-
creasing the ductility of the sand. All the samples were
failed about the same strain of 9.0% when mixed up to
3% of type B fiber. The samples mixed with 4% type B
fiber failed at 7.5% strain. The effects of increasing the
percentages of type A fiber and type B fiber on the fail-
ure strain are shown in Figure 4.
% of fiber
Failure starin
Figure 4. The effect of fibers on the failure starin of the
sand under normal load = 28 kPa.
Table 3. The percentages increase in the angle of internal
friction due to addition of fibers.
Load 28 kPa Fiber A Fiber B
% of fiber φ % increase φ % increase
0 19 0 19 0
1 24 25.6 19 0.5
2 26 35 19 0.5
3 27 40 19 2
4 28 49 18 –8
Load 55 kPa Fiber A Fiber B
% of fiber φ % increase φ % increase
0 19 0 19 0
1 21 1035 20 7
2 24 24 22 17
3 26 38 23 21
4 29 52 25 33
Load 110 kPaFiber A Fiber B
% of fiber φ % increase φ % increase
0 19 0 19 0
1 22 13.7 20 7
2 24 24 22 15
3 27 40 24 28
4 31 64 30 57

48 M. F. ATTOM ET AL.
4.2. The Effect of the Length of the Fiber on the
Shear Strength of Sand
The effects of length of both type A and type B fibers on
shear strength of sand were studied in this research. The
aspect ratio which is defined as the length over diameter
ratio (L/D) was used herein instead of length alone as an
indication for fiber length. Since the two types of fibers
have different diameters, four aspect ratios were used for
each type. The four aspect ratio for type A are L/D =
38.5, 77, 115.5, 154 and for type B are L/D = 10.4, 20.8,
31.2, 41.6 respectively. The four aspect ratios were
studied under three different loads 28 kPa, 55 kPa and
115 kPa. Figures 5 and 6 show the effect of aspect ratio
on shear strength under two normal loads 28 kPa and
110 kPa respectively at 4% type A fiber content by dry
weight of the sand. It is clear from these two figures that
the increase of aspect ratio resulted in increasing the
shear strength. In Figure 5, the shear strength of sand
increased from 11.4 kPa to 14.5 kPa when the aspect ratio
increased from 38.5 to 154 under normal load 28 kPa. At
the same time as shown in Figure 6, the shear strength
increased from 45.1 kPa to 66.1 kPa when the aspect
ratio increased from 38.5 to 154 under normal load equal
to 110 kPa. The percentage in shear strength due to in-
crease in aspect ratio from 38.5 to 154 varies between
27% and 47% under the three normal loads.
It was also noticed that increased in the aspect ratio of
type A fiber resulted in increasing the ductility of the
sand. This observation is clear in Figures 5 and 6. The
sand in all samples at different aspect ratio and under
different normal loads fails at higher strain than if there
is no fiber. Figures 7 and 8 show the effect of type B
fiber on shear strength of sand under two normal loads
28 kPa and 110 kPa at 4% fiber content by dry weight of
the sand.
Horizontal Displacement
(
mm
)
Shear stress (kPa)
Type A fiber
L/D = 115.5
L/D = 154
Figure 5. The effect of the aspect ratio on the shear strength
of the sand at normal load 28 kPa at 4%.
Horizontal Dis
p
lacement
(
mm
)
Shear stress (kPa)
L/D = 115.5
L/D = 154
Figure 6. The effect of the aspect ratio on the shear strear
strength of the sand at normal load 110 kPa at 4% type A
fiber.
Horizontal Displacement (mm)
Shear stress (kPa)
Figure 7. The effect of the aspect ratio on the shear strength
of the sand at normal load 28 kPa at 4% type B fiber.
Horizontal Displacement (mm)
Shear stress (kPa)
L/D = 115.5
L/D
= 144
Figure 8. The effect of the aspect ration on the shear
strength of the sand at normal load 110 kPa at 4% type B
fiber.

M. F. ATTOM ET AL.
49
It is clear from Figure 7 that the type B has a small or
no effect on shear strength if the aspect ratio is less than
20.8 (L = 1.0 cm). Increasing the aspect ratio of more than
20.8 will result in decreasing the shear strength. The shear
strength decreased from 9.6 kPa to 9.2 kPa and 8.6 kPa
when the aspect ratio increased from 10.4 to 31.2 and
41.6 respectively. The reduction in shear strength was
noticed in all samples tested under at small normal load
equal to 28 kPa. This behavior can be attributed to the
plastic-like-surface which makes the sand particles moves
and slip over that surface easier resulted in decreasing
the shear strength.
The effect of aspect ratio of type B fiber on shear
strength under high normal load is shown in Figure 8.
This figure indicated the increase in the aspect ratio will
increase the shear strength under normal load 110 kPa.
The shear strength increased from 49 kPa to 63 kPa
when the aspect ratio increased from 10.4 to 41.6. This
can be explained as the following. As the normal load
increased, the contact surface between sand and the
crimpled surface of the fiber increased. This increase in
the contact surface makes the sand particles harder to
move and thus increasing the shear strength of the sand.
4.3. The Effect of Aspect Ratio on Angle of
Internal Friction
The effect of aspect ratio both fibers on the angle of in-
ternal friction angle of internal of the sand was studied
on Figures 9 and 10. Figure 9 shows that the increase in
the aspect ratio results in increasing the angle of internal
friction of the sand. This increase was noticed under all
different loads. The angle of internal friction increased
from 19o to 31o when the aspect ratio increased from 0.0
to 154 under normal load equal to 110 kPa. The increase
in the angle of internal friction will result in increasing
Aspect ratio for type A fiber
Angle of internal friction
Φ
Figure 9. The effect of aspect ratio of type A fiber on the
angle of internal friction under three different normal
loads.
Aspect ratio for type A fiber
Angle of internal friction
Φ
Figure 10. The effect of aspect ratio of type B fiber on the
angle of internal friction under three different normal
loads.
the shear strength of the sand. Figure 10 studied the be-
havior of sand due to the addition of type B fiber under
three normal loads. As it is shown in this figure the as-
pect ratio has no effect on the angle of internal friction of
the sand under a normal load of 28 kPa. The angle of
internal friction remains about 19o at 10.4, 20.8 and 31.6
aspect ratios. As the aspect ratio increase more than 31.6
it was noticed that the shear strength decreased. On the
other hand and as the normal load increased, it was no-
ticed that the angle ofinternal friction increased. The in-
crease become larger at higher normal load and the angle
of internal friction increased from 10 to 30 at normal
load equal to 119 kPa and aspect ratio equal to 41.6.
5. Practical Consideration
The results of the study have shown that addition of poly-
propylene fibers to sandy soil have improved signifi-
cantly the physical engineering properties. These fibers
may be used practically to increase the shear strength of
sand especially under high loads. The result from this
research concludes that the two types of polypropylene
fibers could be promising materials and can be mixed
with sandy soils in different construction projects to in-
crease sand shear strength with the exception to use type
B fiber at high normal stresses.
6. Conclusions
This research presents the results of using two polypro-
pylene fibers at different percentages and different aspect
ratio to improve the some physical properties of sandy
soil. Based on the test results of this study, the following
conclusions may be drawn out:
1) The shear strength of sand increased by increasing

M. F. ATTOM ET AL.
50
the percentage flat profile fiber with high flexibility (type
A fiber). The increase of in the percentage of the crimped
profile fiber with high relative stiffness (type B fiber)
increased the shear strength at high normal stress.
2) The increase of the percentages of the both type of
fiber will result in increasing the angle of internal friction
of sand.
3) The ductility of sand increased by adding the two
types of fibers.
4) The increase in the aspect ratio resulted in increas-
ing the both the shear strength of the sand and angle of
internal friction. Butter results can be obtained at high.
5) The sand showed no peak strength at the four per-
centages of fibers.
7. References
[1] M. F. Attom, “The Effect of Compactive Energy Level
on Some Soil Properties,” Applied Clay Science, Vol. 12,
No. 1-2, 1997, pp. 61-72.
[2] I. Yilmaz and B. Civelekoglu, “Gypsum: An Additive for
Stabilization of Swelling Clay Soils,” Applied Clay Sci-
ence, Vol. 44, No. 1-2, 2009, pp. 166-172.
[3] A. A. Al-Rawas, A. W. Hago and H. Al-Sarmi, “Effect of
Lime, Cement, and Sarooj (Artificial Pozzolan) on the
Swelling Potential of an Expansive Soil from Oman,”
Building and Environment Journal, Vol. 40, No. 5, 2005,
pp. 681-687.
[4] K. M. A. Hossain, M. Lachemi and S. Easa, “Stabilized
Soils for Construction Applications Incorporating Natural
Resources of Papua New Guinea,” Resouces Conserva-
tion and Recycling Journal, Vol. 51, No. 4, 2007, pp.
711-731.
[5] E. Kalakn, “Effects of Silica Fume on the Geotechnical
Properties of Fine-Grained Soils Exposed to Freeze and
Thaw,” Cold Regions Science and Technology, Vol. 58,
No. 3, 2009, pp. 130-135.
[6] J. D. Nelson and D. J. Miller, “Expansive Soils: Problems
and Practice in Foundation and Pavement Engineering,”
John Wiley and Sons Inc., New York, 1992.
[7] M. M. Abu-Zreig, N. M. Al-Akhras and M. F. Attom,
“Influence of Heat Treatment on the Behavior of Clayey
Soils,” Applied Clay Science, Vol. 20, No. 3, 2001, pp.
129-135.
[8] K. L. Lee, B. D. Adams and J. M. Vagneron, “Reinforced
Earth Retaining Walls,” Journal of Soil Mechanics and
Foundation Division, ASCE, Vol. 99, No. 10, 1973, pp.
745-764.
[9] S. W. Park, R. L. Lytton and J. W. Button, “Forensic
Investigation of Pavement Distortions Using Soil Suc-
tion,” Journal of Transportation Engineering, Vol. 125,
No. 1, 1999, pp. 60-66.
[10] M. N. Fatani, G. H. Bauer and N. Al-Joulani, “Reinforc-
ing Soil with Aligned and Randomly Oriented Metallic
Fibers,” Geotechnical Testing Journal, Vol. 14, No. 1,
1991, pp. 78-87.
[11] S. Ziegler, D. Leshchinsky, H. I. Ling and E. B. Perry,
“Effect of Short Polymeric Fibers on Crack Development
in Clays,” Japanese Geotechnical Society, Vol. 38, No. 1,
1998, pp. 247-253.
[12] T. Yetimoglu and O. Salbas, “A Study on Bearing Capac-
ity of Randomely Distributed Fiber-Reinforced Sand Fills
Overlying Soft Clay,” Geotextiles and Geomembranes
Journal, Vol. 23, No. 2, 2003, pp. 174-183.
[13] M. Esna-ashari and M. Asadi, “A Study on Shear Strength
and Deformation of Sand Soil Reinforced with Tire Cord
Waste,” Proceeding the Fourth Asian Regional Confer-
ence on Geosynthetics, Shanghai, China, 2008, pp. 355-
359.
[14] D. H. Gray and H. Ohashi, “Mechanics of Fiber Rein-
forcement in Sand,” Journal of Geotechnical Engineering,
ASCE, Vol. 1109, No. 3, 1983, pp. 335-353.
[15] T. Park and S. A. Tan, “Enhanced Performance of Rein-
forced Soil Walls by the Inclusion of Short Fiber,” Geo-
textile and Geomembrene Journal, Vol. 23, No. 4, 2005,
pp. 348-361.
[16] D. R. Freitag, “Soil Randomly Reinforced with Fibers,”
Journal of Geotechnical Engineering, ASCE, Vol. 112,
No. 8, 1986, pp. 823-826.
[17] S. Kumar and E. Tabor, “Strength Characteristics of Silty
Clay Reinforced with Randomly Oriented Nylon Fiber,”
Electronic Journal of Geotechnical Engineering, Vol.
127, No. 9, 2003, pp. 774-782.
[18] Y. Cai, B. Shi, C. W. W. Ng and C. Tang, “Effect of
Polypropylene Fiber and Lime Admixture on Engineering
Properties of Clayey Soil,” Engineering Geology Journal,
Vol. 87, No. 3-4, 2006, pp. 230-240.