Coconut fibre or more popularly known as coir fibre is obtained from the outer shell of coconut. It is a suitable example of a waste material that can be utilised as a reinforcing material for soil. The fact that it is easily available makes it all the more suitable for this purpose. The main aim of this research work is to investigate the variation in shear strength parameters of sandy soils by the use of brown coconut fibre as reinforcing material, at a fixed length of 15 mm, using the direct shear test. It also involves the determination of optimum fibre content required for the corresponding maximum value of shear strength paramenter. The results showed that almost 21.5% enhancement in shear strength parameter can be obtained on use of coconut fibre as reinforcement material.

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 7, Issue 3, May–June 2016, pp. 297–305, Article ID: IJCIET_07_03_029
Available online at
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=3
Journal Impact Factor (2016): 9.7820 (Calculated by GISI) www.jifactor.com
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
SHEAR STRENGTH IMPROVEMENT OF
SANDY SOIL USING COCONUT FIBRE
Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar, Bikramjit Deb
U.G. Student, Department of Civil Engineering,
Assam Engineering College, Guwahati, Assam, India
ABSTRACT
Coconut fibre or more popularly known as coir fibre is obtained from the
outer shell of coconut. It is a suitable example of a waste material that can be
utilised as a reinforcing material for soil. The fact that it is easily available
makes it all the more suitable for this purpose. The main aim of this research
work is to investigate the variation in shear strength parameters of sandy soils
by the use of brown coconut fibre as reinforcing material, at a fixed length of
15 mm, using the direct shear test. It also involves the determination of
optimum fibre content required for the corresponding maximum value of shear
strength paramenter. The results showed that almost 21.5% enhancement in
shear strength parameter can be obtained on use of coconut fibre as
reinforcement material.
Keywords: Sandy Soil, Shear Strength Parameter, Internal Friction, Coconut
Fibre, Direct Shear.
Cite this Article: Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar and
Bikramjit Deb, Shear Strength Improvement of Sandy Soil Using Coconut
Fibre. International Journal of Civil Engineering and Technology, 7(3), 2016,
pp.297–305.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=3
1. INTRODUCTION
Soil reinforcement is a wide field of research in the current times. This is because
there are several cases where the soil at shallow depth is not of good quality, and deep
foundations may be expensive. There are several cases where the soil is not of good
quality even at greater depth; and replacement of the soil may not be feasible. Thirdly,
there are situations of underground constructions such as tunnels, or underground air
base and bunkers for defence purposes; in such situations the soil has to be able to
take the overlaying pressure of unsupported walls. In all of these, and several other
situations alike, it is necessary to reinforce the soil with suitable materials, so as to
enable it to have higher efficiency of purpose. The main concept of reinforcement is
the development of friction between the soil and the reinforcement leading to the
transfer of the built up loads of the soil to the reinforcement.

2. Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar and Bikramjit Deb
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As is naturally observed, soil reinforcement is done to a certain extent by the roots
of plants and trees which hold the soil together and prevent soil erosion. This is one of
the main reasons why a lot of emphasis is now being focussed on afforestation and
reduction of deforestation in many parts of the world.
Along with plants, we also have several natural and man made materials that can
be utilised for the purpose of reinforcing the soil. Artificial materials include the likes
of geotextiles and geonets. A few examples of natural materials are hair fibres, sisal
fibres and coconut fibres. These materials can be used for reinforcing the soil. Jute
bags, for example, are very commonly used to reinforce the river embankments and
prevent erosion and reduce damage during floods.
The use of coconut fibres can prove to be a highly efficient means of soil
reinforcement. Coconut fibres are of two types-brown fibres and white fibres. Brown
fibres are obtained from mature coconuts while the white fibres are obtained from
immature coconuts. This paper focuses on the use of brown fibres because these are
thick, coarse, strong, durable and have high abrasion resistance. Also, the use of
coconut fibres can be particularly advantageous to India because of the widespread
cultivation of coconut in the country. As of 2013 records, India’s production of
coconut stands at 11.9 million tonnes, which is the second in the world, behind only
Indonesia and Phillipines. Of the total cultivation of coconut, the four states of South
India account for almost 90% of the production, headed by Coimbatore and Tirupur
regions of Tamil Nadu. The states of Goa, Maharashtra, Odisha, West Bengal, Tripura
and Assam are the producers of the remaining 10%. Thus, we observe that India has a
rich cultivation of coconut, and if the fibres obtained from such high degree of
cultivation can be put to use for reinforcing of soil, it shall prove to be a highly
economic measure of strengthening of soil and with high degree of efficiency.
Following tables illustrate the general properties of coconut fibres:
Table 1 Chemical Composition of Coconut Fibre
Component Percentage
Lignin 45.84
Cellulose 43.44
Hemi-cellulose 0.25
Pection and related compound 3.00
Ash 2.22
Table 2 General Physical Properties of Coconut Fibres
Property Specifications
Length 6-8 inches
Density 1.4 g/cc
Tenacity 10.0
Breaking elongation 30%
Diameter .1mm-.5mm
Modulus of Rigidity 1.8924 dyne/cm²
Swelling in water 30%

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2. MANUFACTURING OF COCONUT FIBRES
The process of manufacturing of coconut fibres involves three major steps-husking,
retting and extraction of fibres. Husking involves the separation of the husk from the
harvested fruits. To obtain good quality coir, the fruits are harvested when still green.
Figure 1 Husking of Coconut Fibres
It is then followed by retting, which is essentially a curing process. The husks are
kept in an environment that encourages microbial action, which leads to
decomposition of the pulp of the husk that allows it to be separated into coir fibres
and coir pith. For fresh water retting, ripe husks are buried in pits along riverbanks,
immersed in water filled concrete tanks or suspended by nets in a river, for a soaking
period of about six months. For salt water retting, green husks are soaked in salinated
fresh water, for a period of eight to ten months.
Figure 2 Retting of Coconut Fibres
Retting is followed by the extraction of fibres. The husks are taken out of water
and washed. The outer skin is peeled off, placed on wooden blocks and beaten for
separating the fibres from the pith. After this separation, fibres are cleaned and dried,
with occasional beating and tossing to remove any impurities remaining in contact
with the fibres.
Figure 3 Extraction of Coconut Fibres

4. Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar and Bikramjit Deb
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3. THE MATERIALS
3.1. SOIL SAMPLE
The sample used for this research work is sand. Sieve analysis, as per the provisions
of IS 383-1970 provided that the sample belongs to Zone III, having a Fineness
Modulus of 3.19
3.2. COCONUT FIBRES
For the purpose of this work, the coconut fibres used were taken in finite lengths of 15
mm. The fibres were extracted from the outer shell of the coconut, soaked in water
and then dried under the sun. As the required quantity of fibres was less, hence shorter
time period of soaking and drying was utilised, as compared to that of large scale
manufacturing process. Following are the properties of the coconut fibres that have
been used for this research work:
Table 3 Properties of Coconut Fibres used
Property Specifications
Length 15 mm
Density 1.4g/cc
Diameter 0.1mm-1.5mm
Major proteins present Lignin, Cellulose
Modulus of Rigidity 1.8924 dyne/cm²
4. METHODOLOGY
Direct shear tests were performed on the soil sample. The initial results shown by the
specimen without any reinforcing materials, at normal stresses of 0.5, 1.0 and 1.5
kg/cm² was first obtained. Next, direct shear test was performed using coconut fibre
as reinforcement at 1.0%, 2.0% and 3.0% by weight of soil. The fibres were randomly
mixed with the soil specimen. Once all the required direct shear tests had been
performed, the stress-strain curves were plot for every individual situation and at
every value of normal stress, from which the maximum shear stress was determined in
each case. This was followed by graphs of maximum shear stress and normal stress to
determine the value of angle of internal friction in each case. The variation of angle of
internal friction with fibre content was studied and the optimum fibre content required
was evaluated.
5. RESULTS OBTAINED
The stress-strain relationship was obtained in each case, of soil without reinforcement
and with reinforcement at various percentages, from which the values of maximum
shear stress were obtained. Then, from the relationship of maximum shear stress and
normal stress, the angle of internal friction was determined in each case. A final
relationship between the angle of internal friction and fibre content was deduced,
from which the maximum value of angle of internal friction and the corresponding
optimum fibre content was obtained.

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5.1. Unreinforced sand
Figure 4 Stress-strain relationship for unreinforced sand
Figure 4 shows the stress-strain relationship for unreinforced soil. The maximum
value of shear stress are 0.32 kg/cm², 0.63 kg/cm² and 0.95 kg/cm² at normal stresses
of 0.5 kg/cm², 1.0 kg/cm² and 1.5 kg/cm² respectively.
Figure 5 Relation between Maximum shear stress and Normal Stress for unreinforced soil
Figure 5 shows the relationship between the maximum shear stress and normal
stress for unreinforced soil. The angle of internal friction obtained when sand is not
reinforced is 32.21ᵒ.
5.2. Reinforced sand
5.2.1. Sand reinforced at 1% by weight
Figure 6 Stress-strain relationship for sand reinforced at 1% by weight
Figure 6 shows the stress-strain relationship when sand is reinforced at 1% by
weight. The maximum value of shear stress are 0.30 kg/cm², 0.72 kg/cm² and 1.12
kg/cm² at normal stresses of 0.5 kg/cm², 1.0 kg/cm² and 1.5 kg/cm² respectively.

6. Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar and Bikramjit Deb
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Figure 7 Relation between Maximum shear stress and Normal Stress for sand reinforced at
1% by weight.
Figure 7 shows the relationship between maximum shear stress and normal stress
for sand reinforced at 1% by weight. The angle of internal friction for sand reinforced
at 1% by weight is 36.05ᵒ.
5.2.2. Sand reinforced at 2% by weight
Figure 8 Stress-strain relationship for sand reinforced at 2% by weight
Figure 8 shows the stress-strain relationship for sand reinforced at 2% by weight.
The maximum value of shear stress are 0.39 kg/cm², 0.75 kg/cm² and 1.25 kg/cm² at
normal stresses of 0.5 kg/cm², 1.0 kg/cm² and 1.5 kg/cm² respectively.
Figure 9 Relation between Maximum shear stress and Normal stress for sand reinforced at
2% by weight.
Figure 9 shows the relationship between the maximum shear stress and normal
stress when sand is reinforced at 2% by weight. The angle of internal friction for sand
reinforced at 1% by weight is 39.14ᵒ.

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5.2.3. Sand reinforced at 3% by weight
Figure 10 Stress-strain relationship for sand reinforced at 3% by weight.
Figure 10 shows the stress-strain relationship for sand reinforced at 3% by weight,
The maximum value of shear stress are 0.37 kg/cm², 0.75 kg/cm² and 1.18 kg/cm² at
normal stresses of 0.5 kg/cm², 1.0 kg/cm² and 1.5 kg/cm² respectively.
Figure 11 Relation between Maximum shear stress and Normal stress for sand reinforced at
3% by weight.
Figure 11 shows the relationship between the maximum shear stress and normal
stress when sand is reinforced at 3% by weight. The angle of internal friction for sand
reinforced at 1% by weight is 37.66ᵒ.
5.3. Optimum Fibre Content
Figure 12 Variation of angle of internal friction with percentage of fibre content

8. Deepjyoti Das, Dhrubajyoti Kaundinya, Raja Sarkar and Bikramjit Deb
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From the relationship between the angle of internal friction and percentage by
weight of reinforcemnt utilised, it has been observed that the maximum value of
internal friction is obtained as 39.20ᵒ. This maximum value is obtained corresponding
to an optimum reinforcement content of 2.1% by weight.
6. INTERPRETATION OF RESULTS
It has been observed that the application of coconut fibres on sand results in an
increase in the shear strength parameter, that is the angle of internal friction. The main
cause of this increase is reasoned out to the fact that in absence of reinforcement, soil
shows brittle failure. However, when coconut fibres are utilised, ductility is provided
to the soil. As has been stated, the main concept behind this is the development of
friction between the soil and the reinforcement. Moreover, we observe that on
application of fibres, the soil gradually shifts to the condition of general shear failure,
which ensures that the analysis of the soil capacity is feasible through analytical
calculations. It has been observed that on application of hair fibres, an increase in the
shear strength parameter of soil is obtained. The shear strength parameter has been
observed to rise upto a certain limit of percentage of reinforcement utilised, and then
it undergoes a reduction with further increase of fibre content. The optimum value of
coconut fibre content, for obtaining maximum value of angle of internal friction is at
2,1%, at which the angle of internal friction is 39.20ᵒ. Hence, it is observed that at the
instant of optimum fibre content or maximum angle of internal friction, the soil
undergoes general shear failure, while in the absence of coconut fibres, the soil is
observed to undergo failure which is the transition between general shear failure and
local shear failure. This thus, simplifies the process of theoretical analysis of bearing
capacity of the sand, as governed by IS 6403-1981.
7. CONCLUSION
The effect of reinforcement of sandy soil by the use of coconut fibres has been
analysed in this paper. The results show an increase in the value of angle of internal
friction, on utilisation of reinforcement. The maximum increase in the parameter is
21.70%, corresponding to an optimum fibre content of 2.1%. Beyond the optimum
content, a reduction in the angle of internal friction is obtained. Thus, it can be
concluded that coconut fibre can be utilised for enhancing the shear strength
parameter of sandy soils, and its easy availability due to widespread cultivation of
coconut in the country can prove to be an efficient and economic measure of
reinforcement of sand. Further research can be conducted on efficient methods of
random placing of the fibres in the soil for yielding better results. Research can also
be conducted on further enhancement of the cultivation of coconut, and the
manufacture of coconut fibre.
REFERENCES
[1] Manjunath K.R, Venugopal G and Rudresh A.N, 2013, Effect of Random
Inclusion of Sisal Fibre on Strength Behavior of Black Cotton Soil, International
Journal of Engineering Research & Technology 2(7) July 2013.
[2] Wajid Ali Butt, Karan Gupta, Hamidullah Naik, Showkat Maqbool Bhat, 2014
Soil Sub–grade Improvement Using Human Hair Fiber, International Journal of
Scientific & Engineering Research, 5(12), ISSN 2229–5518, December 2014.
[3] Rohin Kaushik, An Innovative Technique of Improving the C.B.R Value of Soil
Using Hair fibre” Global Journal of Engineering Science and Researches, ISSN
2348 – 8034, June 2014.

9. Shear Strength Improvement of Sandy Soil Using Coconut Fibre
http://www.iaeme.com/IJCIET/index.asp 305 editor@iaeme.com
[4] D.P. Ray, L.K. Nayak, L. Ammayappan, V B Shambhu, D Nag, 2013, Energy
Conservation Drives for Efficient Extraction and Utilization of Banana Fibre
International Journal of Emerging Technology and Advanced Engineering, 3(8),
ISSN 2250–2459, ISO 9001:2008 Certified Journal.
[5] Bestun J. Nareeman and Mohammed Y. Fattah, 2012, Effect of Soil
Reinforcement on Shear Strength and Settlement of Cohesive- Frictional Soil, Int.
J. of Geomate, OMATE, 3(1) (Sl No 5), pp 308–313, ISSN:2186-2982,
September 2012.
[6] Deepjyoti Das, Raja Sarkar, Bikramjit Deb, Dhrubajyoti Kaundinya, 2016, Shear
Strength Enhancement of Sandy Soil Using Hair Fibre, International Journal of
Innnovative Research in Science, Engineering and Technology, 5(5) ISSN 2319-
8753, May 2016.
[7] http://textilelearner.blogspot.in/2014/01/properties-of-coconutcoir-fiber.html
An Overview of Coconut or Coir Fibre”.
[8] https://en.wikipedia.org/wiki/Coconut#Description, Coconut Fibre.
[9] IS 383-1970 – Grading of fine aggregates
[10] M. Said and T. M. Elrakib, Enhancement of Shear Strength and Ductility For
Reinforced Concrete Wide Beams Due To Web Reinforcement. International
Journal of Civil Engineering and Technology, 4(5), 2013, pp.168–180.
[11] Nagendra Prasad.K, Sivaramulu Naidu.D, Harsha Vardhan Reddy. M and
Chandra.B, Framework For Assessment of Shear Strength Parameters of Residual
Tropical Soils. International Journal of Civil Engineering and Technology, 4(2),
2013, pp.189–207.
[12] IS 2720-(Part XIII)-1986- Direct Shear Test