Soil being the cheapest and readily available construction material has been popular, even though it suffers from being poor in mechanical properties. It has been the constant endeavor of research workers to put forth innovative ideas to improve its mechanical properties to suit the requirements of engineering structures, Vidal in 1968 postulated the new oriented concept of reinforced earth technique. Reinforced earth is a construction material composed of soil fill, strengthened by inclusion of rods, bars, fibers or nets that interact with the soil by means of frictional resistance and act as a coherent mass. It is used in a variety of applications such as retaining structures, embankment, stabilization of subgrade and improvement of soil beneath pavements and footings. Fiber reinforcement technique permits use of natural as well as synthetic fibers for soil reinforcement. In Maharashtra black cotton soil is found in abundance which is highly expansive soil. In present study an attempt has been made to investigate the use of polypropylene fibers for improving properties of locally available soil. The comparison of properties of soil with addition of varying percentages of fibers by dry weight of soil and having different aspect ratios is also carried out. The addition of polypropylene fibers resulted in increase in optimum moisture content and decrease in maximum dry density. Direct shear tests conducted on soil shows increase in value of cohesion and decrease in value of angle of internal friction. With the inclusion of the fibers increase in C. B. R. value and unconfined compressive strength is observed.

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 8, Issue 1, January 2017, pp. 149–154, Article ID: IJCIET_08_01_016
Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=1
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
OPTIMUM USE OF POLYPROPYLENE FIBERS
IMPROVES SOIL PROPERTIES
Dr. M.S. Dixit
Associate Professor, Department of Civil Engineering,
Marathwada Institute of Technology, Aurangabad, Maharashtra, India
ABSTRACT
Soil being the cheapest and readily available construction material has been popular, even
though it suffers from being poor in mechanical properties. It has been the constant endeavor of
research workers to put forth innovative ideas to improve its mechanical properties to suit the
requirements of engineering structures, Vidal in 1968 postulated the new oriented concept of
reinforced earth technique. Reinforced earth is a construction material composed of soil fill,
strengthened by inclusion of rods, bars, fibers or nets that interact with the soil by means of
frictional resistance and act as a coherent mass. It is used in a variety of applications such as
retaining structures, embankment, stabilization of subgrade and improvement of soil beneath
pavements and footings. Fiber reinforcement technique permits use of natural as well as synthetic
fibers for soil reinforcement. In Maharashtra black cotton soil is found in abundance which is
highly expansive soil. In present study an attempt has been made to investigate the use of
polypropylene fibers for improving properties of locally available soil. The comparison of
properties of soil with addition of varying percentages of fibers by dry weight of soil and having
different aspect ratios is also carried out. The addition of polypropylene fibers resulted in increase
in optimum moisture content and decrease in maximum dry density. Direct shear tests conducted
on soil shows increase in value of cohesion and decrease in value of angle of internal friction. With
the inclusion of the fibers increase in C. B. R. value and unconfined compressive strength is
observed.
Key words: Fiber reinforcement, Aspect ratio, Black cotton soil, Polypropylene fiber (PF)
Cite this Article: Dr. M.S. Dixit. Optimum Use of Polypropylene Fibers Improves Soil Properties.
International Journal of Civil Engineering and Technology, 8(1), 2017, pp. 149–154.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=1
1. INTRODUCTION
Amongst recent developments a new construction material obtained by combination of earth and
reinforcement is termed as “Reinforced Earth”. Reinforced earth is formed by association of frictional soil
and tension resistant elements in the form of sheets, strips nets or mats of metal, synthetic fabric or fiber
reinforced plastics and arranged in soil mass in such a way as to reduce or suppress the tensile strain which
might develop under gravity and boundary forces. Soil provides base for the structure and its performance
depends upon local environmental conditions. Soft clay strata are often found unable to bear the load
transferred from the superstructure to the foundation. Soil reinforcement has been in vogue in crude form
since ancient times. Some of the existing historical monuments bear testimony to the use of earth

2. Dr. M.S. Dixit
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reinforcement technique (Jones 1978). No rational study of soil reinforcement had however been made till
a French engineer, Henri Vidal, published his investigation on soil reinforcement in 1968 and started the
use of the term “Reinforced Earth” A variety of earth structures have been built in various parts of the
world in last two decades using reinforced earth principle. Highway embankments, bridge abutments,
retaining walls and earth dams with steep slopes have been built using different types of reinforcements.
Experimental results reported by various investigators Mc-Gown et al (1978), Verma and Char(1978);
Gray and Maher (1989) have shown that fiber reinforcement causes significant improvement in strength
and stiffness of sand. Maher and Gray (1990), Al Refeai (1991) have reported that the strength of
reinforced sand increases with increase in fiber content, aspect ratio and soil fiber surface friction. Al-
Hussaini (1977) reported the results of field experimental studies on a fabric reinforced earth wall. The
reinforced strips used were heavy duty nylon fabric coated with neoprene. Aluminum panels were used as
skin elements. Hoare (1979) analyzing the results of a series of laboratory compression and CBR tests on a
sandy gravel reinforced with randomly distributed synthetic fibers less than 2% by weight observed that
the presence of fibers increased the angle of internal friction and ductility of the soil particularly at low
confining stress.
2. EXPERIMENTAL WORK
2.1. Material
2.1.1. Soil
The soil used in the study was the locally available soil from a farm land near Aurangabad city. The soil
was black cotton soil.
2.1.2. Polypropylene fiber
The polypropylene fibers used in the study was having a diameter of 0.3mm. It was cut into required length
for the aspect ratio of 25,50,75.
Table 1 Geotechnical properties of soil used in study
Sr. No Particulars Value
1 Specific gravity 2.61
2 Liquid limit % 57
3 Plastic limit % 29
4 Plasticity index % 28
5 Optimum moisture content (%) 21.2
6 Maximum dry density (gm/cm3
) 1.54
7 Cohesion (kN/m2
) 30
8 Angle of internal friction (Degrees) 17
9 Unconfined compressive strength(Kg/cm2
) 3.5
3. LABORATORY TESTS
This section describes in detail the plan of experimental work carried out to study the behavior of
randomly distributed polypropylene fiber reinforced soil. The influence of aspect ratio and fiber
concentration on the properties of soil were studied. Geotechnical properties of soil used in study are given
in table 1. The fiber reinforced specimens were prepared by hand mixing the dry soil, water and
polypropylene fibers. The percentage of fiber used in samples was 0.75, 1.5, 2.25 and 3 percent by dry

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weight of soil. The water was added prior to fiber to prevent floating problems. Fiber reinforced soil
samples were prepared at the maximum dry density and the optimum moisture content obtained from
standard proctor tests on reinforced soil. Undrained direct shear tests were conducted on reinforced
samples with varying percentage of fibers of decided aspect ratios. California bearing ratio (C.B.R.) test is
a penetration test developed by California State Highway Department for evaluating the strength of
subgrade soil and base course material for flexible pavement. The tests were conducted under soaked
conditions. Unconfined compression strength tests were conducted on cylindrical specimen at proctors
maximum dry density and optimum moisture conten
4. RESULTS AND DISCUSSION
4.1. Proctor’s Compaction Test
The OMC and dry density test results on black cotton soil with different aspect ratio and fiber content are
reported in table 2 These data indicate that maximum dry density decreases gradually with increase in the
fiber content, which is due to lower density of the fiber than the soil particles. An increase in optimum
moisture content was observed due to adsorption of water particles on the surface of polypropylene fibers.
Table 2 Proctor’s test results for un-reinforced and reinforced soil
Sr No Description Aspect Ratio OMC % MDD
(gm/cm3
)
1 Soil without reinforcement - 21.2 1.54
2 Soil with 0.75% PF 25 21.5 1.50
3 Soil with 1.5% PF 25 21.88 1.47
4 Soil with 2.25% P.F 25 22.10 1.45
5 Soil with 3.0% P.F 25 21.76 1.46
6 Soil with 0.75% P.F 50 21.70 1.49
7 Soil with 1.5% P.F 50 22.20 1.45
8 Soil with 2.25% P.F 50 22.55 1.40
9 Soil with 3.0% P.F 50 21.80 1.43
10 Soil with 0.75% P.F 75 21.75 1.41
11 Soil with 1.5% P.F 75 22.30 1.34
12 Soil with 2.25% P.F 75 23.10 1.33
13 Soil with 3.0% P.F 75 22.01 1.38
4.2. Direct Shear Test
Direct shear tests were conducted on soil samples in un-reinforced and reinforced conditions. The
reinforcement was added in the range of 0.75% to 3.0% with varying aspect ratios. It was observed that
due to addition of polypropylene fibers in the soil the value of cohesion increases with increase in percent
of fibers up to 2.25% and then decreases, while the angle of internal friction decreases with addition of
fibers. The results obtained are summarized in table 3.

4. Dr. M.S. Dixit
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Table 3 Effect of reinforcement on shear strength characteristics of soil
Sr No Description Aspect
Ratio
Cohesion
(KN/m2
)
(φφφφ )
Degree
1 Soil without reinforcement - 30 17
2 Soil with 0.75% PF 25 30.5 16.80
3 Soil with 1.5% PF 25 31.65 16.40
4 Soil with 2.25% PF 25 32.80 16.15
5 Soil with 3.0% PF 25 31.47 16.30
6 Soil with 0.75% PF 50 30.80 16.50
7 Soil with 1.5% PF 50 32.65 15.85
8 Soil with 2.25% PF 50 36.10 15.45
9 Soil with 3.0% PF 50 35.10 15.66
10 Soil with 0.75% PF 75 30.85 16.15
11 Soil with 1.5% PF 75 32.85 15.55
12 Soil with 2.25% PF 75 35.10 15.09
13 Soil with 3.0% PF 75 34.20 15.15
4.3. CBR Test
The CBR tests were conducted on unreinforced soil and soil reinforced with fiber. The tests were carried
out after four days soaking in water. CBR values at different aspect ratio and varying fiber content are
given in table 4. The maximum CBR value in present study was obtained for an aspect ratio of 75 and
2.25% fiber content.
Table 4 CBR values for reinforced and unreinforced soil
Sr No Description Aspect Ratio CBR value
(%)
1 Soil without reinforcement - 4.80
2 Soil with 0.75% PF 25 5.35
3 Soil with 1.5% PF 25 5.80
4 Soil with 2.25% PF 25 6.10
5 Soil with 3.0% PF 25 5.75
6 Soil with 0.75% PF 50 5.52
7 Soil with 1.5% PF 50 6.23
8 Soil with 2.25% PF 50 6.88
9 Soil with 3.0% PF 50 6.20
10 Soil with 0.75% PF 75 5.57
11 Soil with 1.5% PF 75 6.30
12 Soil with 2.25% PF 75 7.06
13 Soil with 3.0% PF 75 6.25

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4.4. Unconfined Compressive Strength
The maximum load that can be transmitted to the sub soil by foundation depends upon the resistance of the
underlying soil to the shearing deformations or compressibility. The results of unconfined compressive
strength conducted on sample are given in table 5. The values of qu increases with increase in fiber content.
Table 5 Unconfined compressive strength values for reinforced and un-reinforced soil
Sr No Description Aspect Ratio qu Kg/cm2
1 Soil without reinforcement - 3.5
2 Soil with 0.75% PF 25 4.10
3 Soil with 1.5% PF 25 4.65
4 Soil with 2.25% PF 25 4.93
5 Soil with 3.0% PF 25 4.60
6 Soil with 0.75% PF 50 4.35
7 Soil with 1.5% PF 50 4.70
8 Soil with 2.25% PF 50 5.03
9 Soil with 3.0% PF 50 4.75
10 Soil with 0.75% PF 75 4.60
11 Soil with 1.5% PF 75 4.88
12 Soil with 2.25% PF 75 5.10
13 Soil with 3.0% PF 75 4.92
5. CONCLUSIONS
Based on the studies carried out following conclusions are drawn:
• The soil used in the present study is found to be fine grained soil and in its present form it is not suitable for
construction and hence needs improvement.
• Soil is modified by addition of polypropylene fibers in the range of 0.75% to 3.0% by dry weight of soil
mass. Addition of polypropylene fibers to the soil resulted in reduction in maximum dry density in the range
of 3% to 14%. Similarly the addition of fibers resulted in increase in optimum moisture content in the range
of 1% to 9% due to adsorption of water particles by the surface of fibers.
• With addition of polypropylene fibers in the soil an increase in the value of cohesion (c) was observed in the
range of 2% to 21% . This trend is observed upto addition of 2.25% of fibers. For addition of 3.0% of fibers
in the soil the value of cohesion decreases. By addition of polypropylene fibers in the soil the angle of
internal friction decreases by 1% to 11% up to 2.25 % addition of fibers and reverses the trend for 3%
addition.
• The C.B.R. value increases in the range of 11% to 47% for addition up 2.25% of polypropylene fibers and
decreases afterwards. Therefore, addition of 2.25% fibers can be considered as an optimum mix.
• The value of unconfined compressive strength increases in the range 17% to 46% up to 2.25% addition of
fibers. Hence it can be concluded that 2.25% addition of polypropylene fibers in the soil can be considered
as an optimum mix for design purposes.

6. Dr. M.S. Dixit
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