International Journal of Engineering Trends and Technology (IJETT) – Volume3 Issue 5 Number4–Oct 2012
EFFECT OF POLYPROPYLENE FIBRE ON INDEX PROPERTIES OF
PROBLEMATIC SOILS
P. Dayakar*, K.V.B. Raju**
*Department of Civil Engg, Bharath University, Chennai,
Tamilnadu, India
** Director, GITAM University, Bengaluru Campus, Bengaluru, Karnataka, India.
ABSTRACT
Geotechnical engineering applications such as land reclamation, construction of highway,
railway and canal embankments require a very large quantity of soil of desirable properties.
But due to the lack of good soil, a geotechnical engineer is forced to use the locally available
problematic soils (having low shear strength high compressibility and swelling nature) after
stabilizing the same with the addition of admixtures. To overcome the difficulties
experienced with problematic soils in geotechnical applications, an attempt is made in this
study to explore the possibilities of utilizing polypropylene fibre to improve the engineering
behaviour of problematic soils. Polypropylene fibre is produced in large quantities in the
synthetic industries. In this study three types of problematic clays are selected to mix the
polypropylene fibre at different proportions varying from 0%, 0.5%, 1%, 1.5% and 2% with
the soils. The index properties with increasing percentage polypropylene fibre are studied and
the results are analyzed. From the results it is concluded that an optimum percentage of 1%
may be used to improve the strength characteristics of the soil.
.
INTRODUCTION
Soil which exhibit volume changes due to variations in moisture contents are defined as
swelling soils. These soils exhibit large amount of swell and shrinkage movements, due to
environmental and seasonal moisture changes. Thus, this movement seriously cause many
structure built on them to damage. The long term performance of a pavement structure is
strongly dependent upon its supporting soil conditions. Therefore, it is imperative to improve
poor properties of native soil such as high plasticity, poor workability, potential for volume
changes and low shear strength in pavement applications. These unsuitable materials
characteristics are traditionally altered using stabilizing materials such as lime and cement.
But in recent times due to explosion in technology the geosynthetic systems that include
fabrics, geogrids and fibre are also in use. In this study an attempt is made to study the effect
of polypropylene fibre to improve the properties of problematic soils..
In conventional methods of reinforced soil construction, the inclusion of strips, fabrics,
bars, grids etc are normally oriented in a preferred direction and are introduced sequentially
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International Journal of Engineering Trends and Technology (IJETT) – Volume3 Issue 5 Number4–Oct 2012
in alternating layers. The discrete fibres are simply added and mixed randomly with soil,
much the same way as cement, lime or other additives. Fibre reinforced soil exhibits greater
extensibility and small losses of peak strength i.e. greater ductility in the composite material
as compared to unreinforced soil or soil reinforced with high modulus inclusions. Therefore,
fibre-reinforced soil can be used as a soil-reinforcement technique with respect to
embankment, sub grade, sub base, and other such problems. However, the data concerning
the impact due to the addition of random discrete fibres on the characteristics of compacted
native or virgin soils are limited. Thus, there is a need for information on the effects of fibres
on the properties of the pavement supporting layers. Ideally, the fibres themselves should be
readily available, non-degradable and capable of being easily blended into the soils and
compacted. The workability of fibre-reinforced materials implies that the fibres should be
resistant to buckling and clumping.
Mahmood R Abdi , Ali Parsapajoh (1997) has observed that consolidation settlement
and swelling of fibre reinforced samples reduces substantially whereas hydraulic conductivity
increased slightly by increasing fibre content and length. The addition of randomly
distributed polypropylene fibres resulted in substantially reducing the consolidation
settlement of the clay soil. Ziegler et al (1998) showed that the previous researches present
strength characteristics of fibre-reinforced soils consisting of randomly oriented discrete
fibres are a function of fibre content and fibre surface friction along with the soil and fibre
strength properties showed that fibre inclusions increased the tensile strength.
1.0 MATERIALS
Soils
Three natural soils are collected in and around the city of Chennai. The soil 1 is collected
from Vyasarpadi, soil 2 is collected form Thiruvanmaiyur and soil 3 is collected from
Taramani. All the soils were collected from a depth of more than 2m below the existing
ground level. Care is taken to collect the soil without any organic matter. The three soils are
selected in such a way that two soils are having high swelling characteristics and one soil is
having swell characteristic of intermediate nature. The index properties of the virgin soils are
shown in table 1.
Table 1 Index Properties of Soils used
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International Journal of Engineering Trends and Technology (IJETT) – Volume3 Issue 5 Number4–Oct 2012
Description
Soil 1
Soil 2
Soil 3
Liquid Limit (%)
44
60
61
Plastic Limit (%)
16
20
10
Plasticity Index (%)
28
40
51
Shrinkage Limit (%)
37.75
21.17
19
Specific Gravity
2.7
2.65
2.6
IS Classification
CI
CH
CH
FSI (%)
20
20
35
Polypropylene fibre
The commercially available polypropylene fiber collected is tested in the laboratory
for its size and specific gravity. The colour of the polypropylene fiber is white and it
contained no particle of size greater than 6mm. The specific gravity of the polypropylene
fiber is found to be 0.91. Fig.1 shows the photograph of the polypropylene fiber used in this
study.
Table 2 Specification of Polypropylene fiber
Material
Polypropylene Fiber
Melt Point, oC
162
Specific Gravity
0.91
Ignition Point, oC
360
Conductivity
Low
Moisture Absorption
Nil
Alkali Resistance
100% Alkali Proof
Acid & Salt Resistance
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High
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International Journal of Engineering Trends and Technology (IJETT) – Volume3 Issue 5 Number4–Oct 2012
Fig 1 Polypropylene fiber
2.0 METHODOLOGY
Series of tests are conducted for determining the basic properties, compaction
characteristics of soil – polypropylene fibre mixtures. The polypropylene fiber is mixed with
soil 1, soil 2 and soil 3 at different percentages varying from 0, 0.5, 1.0, 1.5 and 2.0. The
percentage addition of the fiber is on the basis of weight. The basic tests namely liquid limit,
plastic limit, Shrinkage limit, Specific gravity, proctor compaction test and free swelling
index test are conducted as per the Indian standard codal provisions.
3.0 RESULTS AND DISCUSSIONS
Soil and polypropylene fibre interactions are primarily influenced by types of soil,
and its mineralogical constituent, chemical characteristics of polypropylene fibre. Care is
taken while mixing the fiber with the soil, so that uniform distribution of the fiber is achieved
in the soil fiber mixture. To achieve this, initially the soil and the fiber is mixed in the dry
state and then the water is added accordingly. The values determined from the basic tests are
tabulated in the table 3, for the soil 1 mixed with polypropylene fiber, in the table 4 for the
soil 2 mixed with polypropylene fiber and in the table 5 for the soil 3 mixed with
polypropylene fiber.
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International Journal of Engineering Trends and Technology (IJETT) – Volume3 Issue 5 Number4–Oct 2012
Table 3 Effect of polypropylene fibre on Index Properties of soil 1
0%
Fibre
Properties
0.5%
Fibre
1%
Fibre
1.5%
Fibre
2%
Fibre
Liquid limit, %
44
40
38
43
50
Plastic limit, %
17
20
16
24
23
37.75
28.75
19
20.5
21.03
Specific gravity
2.7
2.65
2.37
2.19
2.1
Dry density, kN/m3
1.71
1.48
1.8
1.49
1.56
Optimum moisture content, %
21.05
18.52
26.09
25
25
20
30
35
40
50
Shrinkage limit, %
Free swelling index,%
Table 4 Effect of polypropylene fibre on Index Properties of soil 2
0%
Fibre
Properties
0.5%
Fibre
1%
Fibre
1.5%
Fibre
2%
Fibre
Liquid limit, %
60
46
35
45
52
Plastic limit, %
20
21
18
25
26
Shrinkage limit, %
21.17
28.86
17.12
32.29
30
Specific gravity
2.65
2.61
2.45
2.42
2.32
Dry density, kN/m3
1.76
1.69
1.8
1.69
1.61
Optimum moisture content, %
21
15
16
16
17
Free swelling index, %
20
30
30
35
40
Table 5 Effect of polypropylene fibre on Index Properties of soil 3
0%
Fibre
0.5%
Fibre
1%
Fibre
Liquid limit, %
61
49
Plastic limit, %
10
Shrinkage limit, %
Specific gravity
Properties
1.5%
Fibre
2%
Fibre
56
55
54
9
12
14
13
19
16.35
12.06
13.75
15.29
2.6
2.48
2.5
2.16
2
1.42
1.48
1.31
1.32
1.34
Optimum moisture content, %
22
19
35
33
20
Free swelling index
35
45
50
60
65
3
Dry density, kN/m
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Effect of Polypropylene Fibre on Liquid Limit
The effect of the polypropylene fibre on liquid limit may be clearly seen from fig 2,
where a plot is made between percentage of polypropylene fibre and liquid limit of the soil.
From the graph it is seen that soil 1 shows decrease in the liquid limit on the addition of 1%
of polypropylene fibre and increase with the addition of polypropylene fibre thereafter. The
soil 2 shows the same behaviour as that soil 1 where the optimum percentage of fiber being
1%. But soil 3 shows decreases in liquid limit at 0.5% and increase at the addition 1% of
polypropylene fibre, which is less than the liquid limit of virgin soil. The liquid limit is an
indication of the compressibility nature of the soils and accordingly the decreasing liquid
limit for soil 1 and soil 2 only indicates that compressibility of the soil decreased, which is
advantageous for the improvement of the soil.
`
Fig 2 Effect of Polypropylene fibre on Liquid limit
Effect of Polypropylene Fibre on Plastic Limit
The effect of the polypropylene fibre on plastic limit may be clearly seen from fig 3,
where a plot is made between percentage of polypropylene fibre and plastic limit of the soil.
From the graph it is seen that soil 1 and soil 2 shows decrease on the addition of 1% . But the
Soil 3 shows decrease on the addition of 0.5%. A decrease in the plastic limit is an indication
of the improvement in the problematic soil.
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International Journal of Engineering Trends and Technology (IJETT) – Volume3 Issue 5 Number4–Oct 2012
Fig 3 Effect of Polypropylene fibre on Plastic Limit
Effect of Polypropylene Fibre on Plasticity Index
Fig 4 shows the plot made between percentage of polypropylene fibre and plasticity
index of the soil. From the graph it is seen that soil 1 shows decrease on the addition of 0.5%
and 0.10% of polypropylene fibre. Soil 2 also shows the same behaviour. Whereas soil 3
shows decrease on the addition of 0.5% and increases on the addition for 0.10% of
polypropylene fibre.
Fig 4 Effect of Polypropylene fibre on plasticity Index
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International Journal of Engineering Trends and Technology (IJETT) – Volume3 Issue 5 Number4–Oct 2012
Effect of Polypropylene Fibre on Shrinkage Limit
The effect of the polypropylene fibre on Shrinkage limit may be clearly seen from fig 5,
where a plot is made between percentage of polypropylene fibre and shrinkage limit of the
soil. From the graph it is seen that soil 1 shows increase on the addition of 0.5% of
polypropylene fibre and decrease on the addition of 10% polypropylene fibre. Soil 2 also
shows the same behaviour as that of soil 1. But Soil 3 shows a decrease in the shrinkage limit
at 0.5% and increase in the shrinkage limit after 0.5% when compared to the virgin soil.
Fig 5 Effect of Polypropylene fibre on Shrinkage Limit
Effect of Polypropylene Fibre on Specific Gravity
To understand the change in the behaviour of the fibre reinforced soil the effect of the
polypropylene fibre on specific gravity is also studied. A plot is made between percentage of
polypropylene fibre and specific gravity of the soil as shown in fig 6. From the graph it is
seen that soil 1 , soil 2 ,and soil 3 decrease constantly after addition for 0.5%, 1%,1.5% and
2.0% of polypropylene fibre. This is true as the specific gravity of polypropylene fibre is
0.91.
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International Journal of Engineering Trends and Technology (IJETT) – Volume3 Issue 5 Number4–Oct 2012
Fig 6 Effect of Polypropylene fibre on Specific gravity
Effect of Polypropylene Fibre on Dry Density
The effect of the polypropylene fibre on dry density may be clearly seen from fig 7,
where a plot is made between percentage of polypropylene fibre and dry density of the soil.
From the graph it is seen that soil 1 and soil 2 show decrease on the addition of
polypropylene fibre where as in soil 3 increase at an addition of 0.5%. Soil 1 and soil 2
increases at 1% addition polypropylene fibre.
Fig 7 Effect of Polypropylene fibre on Maximum dry density.
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Effect of Polypropylene Fibre on OMC
The effect of the polypropylene fibre on OMC may be clearly seen from fig 8, where
a plot is made between percentage of polypropylene fibre and OMC of the soil. From the
graph it is seen that soil 1 shows increase on the addition of 1% polypropylene fiber and same
decreases thereafter. Whereas in soil 2 shows decrease for 0.5% addition and increases
thereafter when compared to virgin soil.
Fig 8 Effect of Polypropylene fibre on Optimum Moisture content
Effect of Polypropylene Fibre on Free Swelling Index
The effect of the polypropylene fibre on FSI may be clearly seen from fig 9, where a
plot is made between percentage of polypropylene fibre and free swelling index of the soil.
From the graph it is seen that soil 1, soil 2 and soil 3 show increase on the addition of
polypropylene fibre corresponding to the virgin soil. Increase in the free swell index may be
attributed to the space occupied by the polypropylene fibers.
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International Journal of Engineering Trends and Technology (IJETT) – Volume3 Issue 5 Number4–Oct 2012
Fig 9 Effect of Polypropylene fibre on Free Swelling Index.
4.0 CONCLUSION
The following conclusions may be drawn from the basic tests conducted on three
different types of soil by adding polypropylene fibre with varying percentage of 0%, 0.5%,
1%, 1.5% and 2%. .
1. The liquid limit is decreased for soil-3 at 0.5% of polypropylene fibre adding
while soil 1 and soil 2 are decreased at adding of 1% of fibre. The decreased
percentages when compared to the virgin soil for soil 1, soil 2 and soil 3 are 16%,
71% and 25% respectively.
2. Plastic limit of soil 1, soil 2 are decreased by adding 1% of polypropylene fibre.
The percentage decrease in plastic limit is 12% for soil1 and 7% is decreased for
soil-3 for the addition of 0.5% fiber.
3. The shrinkage limit is decreased for three soils at 1% of the polypropylene fibre
added.
4. The maximum dry density is increased with the adding of 1% of fibre for soil 1
and soil 2. The increased percentages for both the soils with respect to the virgin
soil are 5% and 3% respectively.
5. The OMC is increased at 1% of fibre for soil 1 and soil 3 and increased
percentages for soil 1 and soil 3 are 12% and 29% respectively.
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International Journal of Engineering Trends and Technology (IJETT) – Volume3 Issue 5 Number4–Oct 2012
It is hence concluded that polypropylene fibre can be effectively used as an admixture
in problematic soils for improving the index properties of problematic soils which is an
indication of improvement in the strength characteristics of the soil.
ACKNOWLEDGEMENTS
Authors acknowledge the Under graduate students Pavan Kumar Channa V, Sabhi Mohan
Ch, Sibil Raju, Siva Mahesh G, and the technical staff of the Soil Mechanics Laboratory,
Department of Civil Engineering for their support in testing of this research project.
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