Engineering Behaviour of Coir Reinforced Clay Soil

This research paper investigates the engineering behaviour of reinforced clay soil with crushed coir through carrying out consolidation test and compaction test. The coir that is crushed is composed of 100% natural fibre which was gotten from coconut husks. The paper discusses the performance of clay soil reinforced with coir fibre, strength behaviour of clay soil reinforced with coir fibres, and effects of coir fibre reinforcement on CBR value and strength of clay soil.

Engineering Behaviour of Coir Reinforced Clay Soil 1
RESEARCH PAPER ON THE ENGINEERING BEHAVIOUR OF NATURAL CLAY
SOIL REINFORCED WITH COIR FIBER
A Research Paper on Coir Fibre By
Student’s Name
Name of the Professor
Institutional Affiliation
City/State
Year/Month/Day

Engineering Behaviour of Coir Reinforced Clay Soil 2
INTRODUCTION
Clay soil is characterized by high compressibility and low permeability because of its
high capacity of holding water. The absorption of water leads to the behaviour of soil
plasticity which does not disintegrate easily and can be deformed or moulded. Since the water
holding capacity of the soil is high, it gives the soil another feature of low permeability which
leads to swelling and hence expansion of soil making resulting in the soil being weaker.
These features of clay soil make not recommended for holding or supporting huge loads of
any structure above the soil surface and also difficult to be used in engineering and
construction industries.
For the minimization of these negative characteristics of the clay soil, the soil should
be reinforced with numerous materials by the use of techniques of ground improvement. This
research paper aims at investigating the engineering behaviour of reinforced clay soil with
crushed coir through carrying out consolidation test and compaction test. The coir that is
crushed is composed of 100% natural fibre which was gotten from coconut husks. The reason
why the coir of the coconut husks was used was that it is economically viable, easy to handle
and also very light. The clay soil that was used in this experiment was gotten from RIPAS
Bridge site with the liquid limit of 38.4%, plasticity limit of 22.5%, and plasticity index of
15.9% (Ahmad, 2010).
The clay soil went through processes like crushing and drying followed by Atterberg
limit test and sieving to determine its primary characteristics. The clay soil reinforced and
non-reinforced soil with inclusion percentages of 2.0%, 1.5%, and 1.0% of coir that is
crushed went through compaction test to determine the impact on the moisture content and
dry density. In the test for consolidation, the clay soil samples were reinforced with numerous
inclusion percentages of 2.0%, 1.5%, 1.0%, 0.5%, and 0% of the crushed coir. This is dome

Engineering Behaviour of Coir Reinforced Clay Soil 3
to evaluate the effects on consolidation behaviour as a result of the inclusion of crushed coir
(Arora, 2011).
Performance of Clay Soil Reinforced with Coir Fibre
Majority of the soils have enough shear strength and good compressive strength.
However, they have power tensile strength. This problem can be solved through carrying out
techniques of soil improvements which are aimed at soil reinforcement and soil stabilization.
The tests which can be carried out to determine the impacts of adding coir to the clay soil can
be done through model footing tests and Proctor compaction tests. The Standard Proctor
compaction tests were performed to evaluate the impacts of clay soil reinforced with coir
fibre on the moisture content and the dry density of the soil (Babu, 2014).
The clay soil reinforced and non-reinforced soil with inclusion percentages of 2.0%,
1.5%, and 1.0% of coir that is crushed went through compaction test to determine the impact
on the moisture content and dry density. The Standard proctor’s compaction test by the use of
light compaction was done in relation to the relevant IS standard so as to find out the
optimum moisture content and maximum dry density for the unreinforced and reinforced clay
soil using coir fibre (Babu, 2011). The results of the dry density versus moisture content
gotten from the experiment can be graphically represented as shown in the figure below:
Figure 1: Dry density vs Moisture content curves for the reinforced and non-
reinforced coir fibre (Dixit, 2012)

Engineering Behaviour of Coir Reinforced Clay Soil 4
From the results, the optimum moisture content and maximum dry density for the
unreinforced clay soil is 20% and 1.85 kg/m3 respectively. The maximum dry density do not
depend on the amount or percentage of fibre in the soil. The dry weight is higher due to
absence of fibre which reduces the dry weight. The optimum moisture content and maximum
dry density for the coir reinforced clay soil with 2.0% coir fibre is 18.5% and 1.84 kg/m3
respectively. 2.0% fibre will make this soil to have a higher moisture content and lower dry
weight. The dry density will be lower than that of unreinforced soil while the moisture
content will be higher than that of unreinforced soil. The decrease in density of the reinforced
fibres is as a result of fibre filaments which have less specific weight when compared to soil
grains and fibres prevent particles of soil from approaching to each other. The increase in
moisture content is due the results of the fibres having a greater water absorption capacity
than the surrounding soil (Kalkan, 2013).
The optimum moisture content and maximum dry density for the coir reinforced clay
soil with 1.5% coir fibre is 18% and 1.72 kg/m3 respectively. When 0.5% fibre is used, the
dry density will be lower and the moisture content will be lower than that of 2.0% fibre
inclusion. The fibre filaments which have less specific weight will be less in the 1.5%
inclusion making the density to be slightly higher and the absorption capacity of the less fibre
content will also be lower.
The optimum moisture content and maximum dry density for the coir reinforced clay
soil with 1.0% coir fibre is 19% and 1.64 kg/m3 respectively. The overall results show that
the maximum dry density reduces and the optimum moisture content increases with an
increase in the fibre content (Dutta, 2015). In this case, the amount of fibre is greatly reduced
in the soil making the specific weight to be higher since there is less fibre and also the
absorption capacity of the soil as a result of the fibre content will also be lower (Jiang, 2014).

Engineering Behaviour of Coir Reinforced Clay Soil 5
Strength Behaviour of Clay soil Reinforced with Coir Fibres
Investigations on the effects of the coir fibre reinforced and unreinforced clay soil on
the shear strength behaviour of the clay soil have been done by researchers. This is because
the disposal of the clay soil has threatened the sustainability of the environment and has also
led to environmental problems. In the experiment performed by Vishwas N. Khatri to
determine the strength behaviour of clay soil reinforced with coir fibre, the specimens for
unreinforced clay soil were prepared at 12% optimum moisture content and dry unit weight
18.6kN/m3 (Estabragh, 2011). The table below shows the optimum moisture and dry unit
weight of reinforced and unreinforced clay soil samples:
Table 1: Optimum moisture content and dry weight of reinforced and unreinforced
clay (Estabragh, 2011)
For the prediction of the response of the stress-strain of the clay soil, a two-parameter
dependent hyperbolic model should be used. This model can be defined as:
Where ε is the training failure and ‘a’ and ‘b’ are the material constants. The inverse of ‘a’
and ‘b’ gives the ultimate strength and initial elastic modulus respectively (Jiang, 2014). The
predicted curves of stress-strain along with the results of the respective experiment for given
values selected for the fibre content and confining pressure as shown in the figure below:

Engineering Behaviour of Coir Reinforced Clay Soil 6
Figure 2: Respective experimental values of fibre content and confining pressure
The results of the compaction test show that the optimum content of moisture of the
reinforced clay with treated and untreated coir increases in the increase in the coir fibre
content. This is true theoretically since the treated CCL4 coir fibre inclusion to the clay soil
will lead to cohesion improvement and greater friction. The major shortcoming of the
reported work in the literature is that it may be true that the optimum content of moisture of
the reinforced clay with treated and untreated coir increases in the increase in the coir fibre
content, however, there is a limit through which an increase in coir fibre will increase
optimum moisture content (Jiang, 2014).
It can be noted that these are consistencies from the literature on changes in the
material behaviour and properties through coir inclusion and the slight variations are as a
result of different types of clay soil used in the research. The findings from the literature may
affect the methodology that will be used during the experiment such as sample preparation.
This is because the samples will have to be prepared in accordance with the literature for the
consistencies to be achieved. The clay soil samples should be reinforced with 1.6%, 0.8%,
and 0.4% coir fibre contents to determine the shear strength behaviour of the clay soil
(Kalkan, 2013).
In the experiment performed by Shivanand Mali to determine the strength behaviour
of cohesive soils reinforced with fibres, the stiffness and strength of the soil was investigated

Engineering Behaviour of Coir Reinforced Clay Soil 7
with response to coir fibre reinforcement. The results of the stress versus strain response for
different content of fibre is as shown in the figure below:
Figure 3: Stress against strain curves for coir fibre reinforced soil
The curves in the figure above shows that the deviator stress at failure increases with
the content of fore and takes place at approximately 10% to 18% of strain. The optimum
content of fibre matching to optimum strength improvement is found to be 2.0% to 2.5%.
Optimum improvement is acquired with 15 mm fibre length.
The comparison between the experiments performed to evaluate the strength
behaviour of cohesive soils reinforced with fibres by Vishwas N. Khatri and Shivanand Mali
shows that the experiment performed by Vishwas N. Khatri improves the soil better since it
pts into considerations the different confining pressures ranging from 78kPa to 310kPa
(Dutta, 2015).
Effects of Coir Fibre Reinforcement on CBR Value and Strength of Clay Soil
Many soil tracks around RIPAS Bride site can be characterized as being expansive
and also have undergone volumetric variations leading to variations in the soil's moisture
content. There is need to take some necessary actions on the soil on this site or else there can

Engineering Behaviour of Coir Reinforced Clay Soil 8
be some serious structural damages if no action is taken. Research carried out to determine
the effects of coir fibre reinforcement on CBR value and strength of natural clay obtained
from RIPAS Bridge site (Kalkan, 2013).
In the experiment performed by Neelu Nandan Vibhakar, the length of coir fibre used
for this experiment is of diameter 0.1mm and length 5mm. When CBR test was done on the
resistance to penetration of the reinforced clay soil, there was no increase after 2% coir
inclusion. The rise in the resistance to penetration of the clay soil is as a result of the
improvement in the particles interlocking amongst the elements of the coir fibre and the bond
between soil particles and coir fibres (Ranjan, 2011). The observations for the index
properties of the clay soil is as shown in the figure below:
Figure 2: Index properties of the clay soil (Sayida, 2014)
From the tests carried out in during the research on the effects of coir fibre reinforcement on
CBR Value and strength of clay soil, the results of the tests include:
Toughness index = 2.88: The toughness index of 2.88 shows that the soil sample used in this
experiment is clay in nature.
Consistency index = 0.75: This value of consistency index that has been determining to be
between 1 and 0 shows that the consistency of the clay soil used in this experiment is soft.

Engineering Behaviour of Coir Reinforced Clay Soil 9
Liquidity index = 0.25: This value of the liquid index that has been calculated to be 0.25
shows that the clay soil used is intermediate between liquid and stiff state condition (Ranjan,
2013).
Plasticity index = 0.49: This value of plasticity index that has been calculated to be 0.49
shows that the soil is highly plastic.
Plastic limit = 23%
Liquid limit = 72%
Water content = 35%
Specific gravity of the clay soil = 2.60
Differential free swell index = 65%: The value of free swell that has been calculating to be
65% shows that the samples of clay soil used in this experiment have a higher degree of
expansion (Sayida, 2014).
From the curve of strain versus stress below, the optimum stress provides the unconfined
compressive strength (qu).
Figure 3: Stress against strain curve
In case of φ = 0 situations, the cohesion or shear strength of the clay soil may be assumed to
be equivalent to half the strength of unconfined compression.
C = (qu)/2 = 161.4 kPa/2 = 80.7 kPa
Optimum moisture content = 14%
Maximum dry density = 1.710 g/cc
The major shortcoming of the reported work in the literature is that it failed to
indicate why the CBR value of the clay soil only increases with the addition of coir fibre up
to 2% of the soil's weight. This is important since it will help a researcher to know the
optimum fibre inclusion that should be used. The literature also failed to indicate why the

Engineering Behaviour of Coir Reinforced Clay Soil 10
optimum coir content is 2% and why there will no observable improvement in the value of
CBR. There are consistent trends from the literature on the variations in the behaviour of the
material and properties through the inclusion of fibre content in bothering the literature and
on the experiment done. The findings from the literature are critical in determining the
percentages of coir fibre inclusion that would be used when carrying out the experiment
(Estabragh, 2011).
In the experiment performed by Wajid Ali Butt on the determination of strength
behaviour of clay soil reinforce by human hair as a natural fibre, randomly distributed
samples of clay soil were tested for its engineering properties by performing tri-axial and
CBR on numerous samples by the sue of diverse fibre percentages and comparing the
outcome with clay soil that non-reinforced. Fibres of average diameter of 50ựm and average
length of 25mm were used in this experiment. The results of the experiment of the effect of
human hair on CBR and undrained shear strength of the soil is as shown in the figure below:
Figure 4: CBR against percentage human hair content
The figure above shows that the optimum quantity of human hair fibre to enhance the
maximum value of CBR at 205 mm penetration is 2.0%. The increase in the value of CBR as
a result of addition of human hair fibre to the clay soil may be as a result of improved
interfacial adhesive between the particles of soil and the fibre. However, the decrease in the

Engineering Behaviour of Coir Reinforced Clay Soil 11
value of CBR beyond the optimum content of fibre may be as a result of the increase in
interaction between fibres to fibre.
When the experiments on the effects of coir fibre reinforcement on CBR value and
strength of clay soil performed by Wajid Ali Butt and Neelu Nandan Vibhakar are compared,
it can be noted that experiment performed by Wajid Ali improved the soil better since the
experiment considered the penetration of the fibre content into the soil making the results to
be more effective. When considering ways of improving the clay soil by the use of fibre
inclusion, it is advisable to consider the penetration of the fibre for every percentage of fibre
content used in reinforcing the soil.
Consolidation Characteristics of Clay Soil Reinforced with Coir Fibre
The effects of coir fibre reinforced clay soil has been scrutinized by many researchers
who have been involved directly in engineering and construction of structures on the clay
soil’s top. Consolidation of clay soil that is saturated is done because of the expulsion of
water under sustained, static load. The characteristics of consolidation of the clay soil are
necessary for predicting the rate and magnitude of the settlement of the soil under
consideration. The determination of the optimum moisture content was performed through
Standard Proctor compaction test by randomly mixing the fibres with water all over the clay
soil.
In the experiment performed by A. R. Estabragh, numerous consolidation test was
also done with variations in the fibre contents between 1% and 0% with an increase of
percentage dry weight of 0.2%. Where p is the pressure applied and v is the specific volume
(v=e+1). The region where the two linear segments meet is used in determining the
preconsolidation pressure. Cc is the elastoplastic zone and Cs is the slope of the elastic zone
and these values were determined as shown in the table below:

Engineering Behaviour of Coir Reinforced Clay Soil 12
Table 3: Parameters of shear strength and consolidation for fibre reinforced and
unreinforced clay soil (Sayida, 2014)
The stress deviator increases up to 15% axial strain for the clay soil, however, the
tests of the soil samples for the unreinforced soil proceeds up to 20% axial strain. These
results show that at any provided confining pressure, increasing the quantity of fibre
improves the strength of clay soil. It is also clear that the samples of reinforced and
unreinforced clay minimizes pre-consolidation pressure and the Cs and Cc values normally
increase with the increase in the coir fibre content. When the fibre is added to the clay soil,
some particles of soil are substituted with fibres and they conquer the pores amongst the
particles of soil which lead to increase in the ratio of the void of the mass of the clay soil. The
coefficient of change in volume (mv) and coefficient of consolidation (Cv) in the range of
pressure of 200 to 400 kPa can also be determined (Ahmad, 2010).
In the experiment performed by Rabindra Kumar, the parameters of consolidation
namely mv, Cv, and Cc for clay soil Reinforced with percentage coir fibre inclusion of 0, 0.2,
0.4, 0.6, 0.8, and 1.0 is as shown in the table below:

Engineering Behaviour of Coir Reinforced Clay Soil 13
From the tables above, it can be observed that the values of Cc decreases with the increase of
inclusion of coir fibre in the natural clay up to 0.8% fibre content and then after that the Cc
values start increasing. The minimum Cc value is observed at coir fibre content of 0.8% and
0.6%. This can be due to the volume occupied by the fibre being more resulting to more
interaction of fibre to fibre and hence there will be dominance in fibre compression.
When the experiment done by A. R. Estabragh and Rabindra Kumar are compared, it
is noted that the consolidation test performed by Rabindra Kumar was better that the same
test performed by A. R. Estabragh since the percentages of fibre inclusion used by Rabindra
Kumar ranges between 0% to 0.1% making it faster to achieve the required degree of
consolidation. The time required to attain the primary consolidation decreases for the
reinforced clay soil for a given drainage path and a given degree of consolidation. The
experiment performed by Rabindra Kumar is also more effective since he compared the
reinforcement of the soil with two different types of fibres namely polypropylene and coir
fibres.
Conclusion
This research paper aims at investigating the engineering behaviour of reinforced clay
soil with crushed coir through carrying out consolidation test and compaction test. The coir
that is crushed is composed of 100% natural fibre which was gotten from coconut husks. The

Engineering Behaviour of Coir Reinforced Clay Soil 14
clay soil that was used in this experiment was gotten from RIPAS Bridge site with the liquid
limit of 38.4%, plasticity limit of 22.5%, and plasticity index of 15.9%. The characteristics of
the clay soil that have been critically reviewed in this research paper include strength
behaviour of the reinforced clay, shear strength behaviour of the reinforced clay soil,
performance of the coir reinforced clay soil, and consolidation characteristics of the
reinforced clay.

Engineering Behaviour of Coir Reinforced Clay Soil 15
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