International Journal of Engineering Trends and Technology (IJETT) – Volume 35 Number 4- May 2016
Experimental and Analytical Investigation of
Artificial Fiber Reinforced Subgrade Soil for
Flexible Pavement
V.Sathiya priya#1, Dr.P.D.Arumairaj*2
#
P.G Student, Department of civil engineering, GCT, Coimbatore, Tamil nadu, India.
*
Professor, Department of civil engineering, ACCET, Karaikudi, Tamil nadu, India.
Abstract — Damages in flexible pavements are
mostly due to weak soil subgrade. In this work,
reinforced earth technique is used to improve the
sub grade soil. It helps to improve the compaction
characteristics of soil besides reduction in the
permeability and compressibility. It also helps to
increase its shear strength and the bearing capacity.
Proctor’s compaction test, Unconfined compressive
strength test, Unsoaked CBR and soaked CBR test
are conducted on locally available soil reinforced
with artificial fiber. Addition of artificial fiber
results in reduction in the design thickness of flexible
pavement. The software PLAXIS-2D and IITPAVE
are used to evaluate the performance of
unreinforced and artificial fiber reinforced
pavement. Traffic Benefit Ratio (TBR) arrived at
indicates that addition of artificial fibers improves
the service life of pavement.
Keywords — Proctor’s compaction test, UCS test,
Unsoaked CBR, soaked CBR, Artificial fiber,
PLAXIS-2D, IITPAVE, TBR.
I. INTRODUCTION
Improvement of subgrade soil is done either by
mechanical method or by adding additives to the
subgrade soil. In subgrade soil, fibers are added by
randomly or reinforced in layers. Randomly
distributed fiber-reinforced technique is mostly used
in geotechnical engineering. Improvement of
strength is due to surface friction between the fiber
and soil. Use of artificial fiber in soil as
reinforcement gives improvement of soil properties.
Artificial fiber has synthetic fibers and non synthetic
fibers. Some examples of artificial fibers are
Polyester, polypropylene, polyethylene, nylon, rayon,
glass, steel, spandex, acrylic and kevlar. Soil which
is used in this project is collected from Kalapatti
road, Coimbatore.
As per Indian Roads Congress (IRC: 37-2001)
California Bearing Ratio (CBR) value of subgrade
soil must have minimum two per cent. If CBR of the
subgrade soil is less 2%, a capping layer of 150mm
thickness of material should be provided. Soil which
is collected from Kalapatti road has CBR value of
1.84%. Improvement of soil has to be done to avoid
capping layer.
ISSN: 2231-5381
Geotechnical properties of clay such as particle
size distribution, Atterberg’s limits, specific gravity,
Differential free swell, Optimum Moisture Content
(OMC), Maximum dry density (MDD), unconfined
compressive strength (UCS) and CBR values are
determined. Based on the results, the clay is
classified as clay of high compressibility (CH) as per
BIS. An experimental investigation was done in this
project to study the effect of Polyester fiber (PF),
Polypropylene fiber (PPF), Glass fiber (GF), Nylon
fiber (NF) and steel fiber (SF) as reinforcing
material, in subgrade of flexible pavement system to
determine the on compaction characteristics, UCS
and CBR.
The design of pavement with and without
artificial fiber reinforcement is done to compare the
reduction in thickness of pavement. In addition to
this, Software analysis of Pavement is done by using
PLAXIS and IITPAVE. The performance of
polyester fiber, polypropylene fiber, glass fiber,
nylon fiber and steel fiber reinforced pavements is
evaluated using the softwares. Maximum vertical
compressive strain is determined from PLAXIS.
Allowable vertical compressive strain is evaluated
from IITPAVE. Traffic Benefit Ratio (TBR) of
pavement structure is determined using maximum
vertical compressive strain as calculated using
PLAXIS. The suitability and performance of the
five artificial fibers are discussed and compared.
II. MATERIALS AND TEST METHODS
A. Soil used
Soil sample is collected from Kalapatti raod,
Coimbatore. The sample is collected at a depth of
0.3m below the ground surface. The soil used for
analysis is identified as clay.
B. Soil properties
The properties of clay as obtained from soil
analysis are shown in table I.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 35 Number 4- May 2016
TABLE I
PROPERTIES OF CLAYEY SOIL
S.NO
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Properties
Natural Moisture Content
Specific Gravity
Percentage Gravel
Percentage sand
Percentage Silt
Percentage Clay
Liquid limit
Plastic limit
Shrinkage limit
Differential Free Swell
Soil Classification
OMC
MDD
UCS (qu)
Unsoaked CBR
Soaked CBR
Results
27.23%
2.73
02.05%
27.25%
07.10%
63.60%
57%
14.9%
11.4%
40%
CH
21.50%
1.655g/cc
80 KN/m2
2.51%
1.84%
Fig.1 OMC values with artificial fibers
C. Artificial fibers
Artificial fibers namely PF, PPF, NF, GF and SF
are used as reinforcing materials. The properties of
fibers are shown in table II.
TABLE III
PROPERTIES OF FIBERS
Property
Length(mm)
Tenacity
(gm/den)
Elongation (%)
Moisture
regain(%)
Density(g/cc)
Aspect ratio
PF
30
5-7
PPF
6
5
GF
100
6.5
NF
75
7
SF
24
-
20
0.4
30
0
3
0
30
4
-
1.4
200
0.9
-
2.5
-
1.14
-
OMC of the soil with addition of PF decreases
from 21.5% to 14.5% for various fiber content up to
2%. OMC of the soil with addition of PPF decreases
from 21.5% to 14% for various fiber content up to
1%. OMC of the soil with addition of GF decreases
from 21.5% to 15% for various fiber content up to
1.25%. OMC of the soil with addition of SF
decreases from 21.5% to 14.5% for various fiber
content up to 10%. The decrease in OMC is due to
very low moisture absorbing capacity of PF, PPF,
GF and SF. OMC of the soil with addition of NF
increases from 21.5% to 23.2% for various fiber
content up to 1%. The increase in OMC is due high
moisture absorbing capacity of NF.
The variation in maximum dry density with
addition of the artificial fibers under light
compaction is shown in figure 2.
8
50
D. Methodology
Laboratory tests such as Standard Proctor
compaction UCS and CBR are conducted on the
subgrade soil with various percentages of PF (0.5%,
1%,1.5%, 2%), PPF (0.25%, 0.50%, 0.75%, 1%), GF
(0.25%, 0.5%, 0.75%, 1%, 1.25%), NF (0.25%,
0.50%, 0.75%, 1%) and SF (2%, 4%, 6%, 8%, 9%,
10%).
III. RESULTS AND DISCUSSION
A. Standard Proctor’s compaction
The variation in Optimum moisture content with
addition of various artificial fibers under light
compaction is shown in figure 1.
ISSN: 2231-5381
Fig.2 MDD values with artificial fibers
MDD decreases with addition PF upto 1.5% and
increases beyond 1.5%. MDD decreases with
addition PPF upto 0.75% and increases beyond
0.75%. The decrease in MDD is due to lower density
of PF and PPF. MDD of the soil decreases with
addition of NF. The decrease in MDD is due to
lower density of NF. MDD of the soil increases with
addition of GF. MDD of soil increase with addition
of SF. The increase in MDD is due to higher density
of GF and SF.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 35 Number 4- May 2016
B. Unconfined compressive strength
The variation in Unconfined compressive strength
with addition of various artificial fibers under light
compaction is shown in figure 3.
from 2.51% to 11.05% upto1% of GF beyond which
it decreases. Unsoaked CBR value of the sub grade
soil increases from 2.51% to 7.2% upto 0.75% of NF
beyond which it decreases. Unsoaked CBR value of
the sub grade soil increases from 2.51% to 13.4%
upto9% of SF beyond which it decreases.
The variation in Soaked CBR values with
addition of various artificial fibers under light
compaction is shown in figure 5.
Fig.3 UCS values with artificial fibers
UCS of the sub grade soil increases from
80kN/m² to 188.61kN/m² upto 1.5% of PF beyond
which it decreases. UCS of the sub grade soil
increases from 80kN/m² to 266.11kN/m² upto 0.75%
of PPF beyond which it decreases. UCS value of the
soil increases from 80kN/m² to 198.1kN/m² upto 1%
of GF beyond which it decreases. UCS of the sub
grade soil increases from 80kN/m² to 138.2kN/m²
upto 0.75% of NF beyond which it decreases. UCS
of the sub grade soil increases from 80kN/m² to
297.2kN/m² upto 9% of SF beyond which it
decreases.
C. California Bearing Ratio
The variation in Unsoaked CBR values with
addition of various artificial fibers under light
compaction is shown in figure 4.
Fig.5 Soaked CBR values with artificial fibers
Soaked CBR value of the sub grade soil
increases from 1.84% to 2.68% upto1.5% of PF
beyond which it decreases. Soaked CBR value of the
sub grade soil increases from 1.84% to 3.35% upto
0.75% of PPF beyond which it decreases. Soaked
CBR value of the sub grade soil increases from
1.84% to 4.86% upto1% of GF beyond which it
decreases. Soaked CBR value of the sub grade soil
increases from 1.84% to 3.52% upto 0.75% of NF
beyond which it decreases. Soaked CBR value of the
sub grade soil increases from 1.84% to 5.2% upto
9% of PF beyond which it decreases.
IV. DESIGN OF PAVEMENT
The input data for the design of pavement is given
below
1) Two-lane single carriageway
2) Initial
traffic
at
the
year
of
construction=1200CV/day
3) Traffic growth rate per annum =7.5%
4) Design life
=15 yrs
5) Vehicle damage factor
=3.5
6) Distribution factor
=0.75
Design results for unreinforced and fiber
reinforced pavements are shown in table III.
Fig.4 Unsoaked CBR values with artificial fibers
Unsoaked CBR value of the sub grade soil
increases from 2.51% to 5.69% upto1.5% of PF
beyond which it decreases. Unsoaked CBR value of
the sub grade soil increases from 2.51% to 6.25%
upto 0.75% of PPF beyond which it decreases.
Unsoaked CBR value of the sub grade soil increases
ISSN: 2231-5381
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International Journal of Engineering Trends and Technology (IJETT) – Volume 35 Number 4- May 2016
TABLE IIIII
DESIGN RESULTS FOR UNREINFORCED AND FIBER
REINFORCED PAVEMENTS
Reinforcing
material
Soaked
CBR
value
(%)
Total
pavement
thickness
(mm
Plain soil
PF
PPF
GF
NF
SF
1.84
2.91
3.35
4.86
3.52
5.2
920
840
790
715
780
700
Reduction
in
pavement
thickness
(mm)
80
130
205
140
220
V. SOFTWARE ANALYSIS
From plaxis maximum vertical strain and
maximum vertical deflections are calculated. From
IITPAVE allowable vertical strain and allowable
vertical deflections are calculated. Allowable strain
and allowable deflections must be more then the
value of maximum stain and maximum deflections
developed in the pavement structure. Figure 10.6
shows the vertical deflection values from PLAXIS
and IITPAVE. Figure 10.7 shows the vertical strain
values from PLAXIS and IITPAVE. Figure 10.8
shows the Traffic Benefit Ration from PLAXIS.
Fig.8 TBR values from PLAXIS
VI. CONCLUSION
Based on the experimental studies, pavement design
and analytical studies the following conclusions
were drawn.
1.
2.
3.
4.
5.
Fig .6 Vertical deflection values from PLAXIS and
IITPAVE
6.
7.
8.
9.
Fig.7 Vertical strain values from PLAXIS and
IITPAVE
ISSN: 2231-5381
The selected soil sample is found to have
low strength with Soaked CBR value of
1.84%. It indicates that subgrade has to be
improved.
Artificial fibers reinforced subgrade
improves the strength properties of soil
which makes the subgrade suitable for
pavement, without capping layer.
The optimum Polyester and Polypropylene
fiber content is found as 1.5% and 0.75%
respectively. The optimum Glass, Nylon
and Steel fiber content is found as 1%,
0.75% and 9% respectively based on CBR
and UCS test.
The Soaked CBR value of the sub grade
soil is increased to 2.68% at optimum fiber
content (1.5%) for PF and 3.35% at
optimum fiber content (0.75%) for PPF.
The Soaked CBR value of the sub grade
soil is increased to 4.86% at optimum fiber
content (1%) for GF, 3.52% at optimum
fiber content (0.75%) for NF and 5.2% at
optimum fiber content (9%) of SF.
It is concluded that there is a considerable
reduction in the thickness of pavement for
artificial
fiber
reinforced
subgrade
compared to unreinforced subgrade.
The PLAXIS analysis shows that there is
reduction in deflection and Strain value in
artificial fiber reinforcement in Subgrade.
Based on the output obtained from PLAXIS
and IITPAVE, it is found that maximum
vertical strain values are less than the
values of allowable vertical strain. It
indicates that the designed thickness of the
pavement layers is sufficient.
Steel fiber reinforced subgrade soil will
gives maximum improvement in CBR
value.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 35 Number 4- May 2016
10.
11.
Traffic Benefit Ratio is maximum for steel
fiber reinforced pavement.
Of the five artificial fibers the use of steel
fiber gives the best results followed by
polyester, polypropylene, glass, nylon
fibers in chronological order.
ACKNOWLEDGMENT
It takes me immense pleasure in expressing my
sincere gratitude and heartfelt thanks to my guide Dr.
P.D.ARUMAIRAJ, Ph.D.,Professor in Department
of Civil Engineering (soils), ACCET for his
guidance, inspiration, constant encouragement,
valuable suggestions, motivation and unstained help
during this work.
I express my heartfelt thanks to all the faculty
members of Department of Civil Engineering (Soils)
for their help and suggestions in doing this thesis
work. I thank all non-teaching staff members for
their assistance rendered for completing the thesis.
This dissertation would not have been possible
without the support of my friends of Geotechnical
Engineering Department, my family members and
the help of several individuals who extended their
valuable assistance during the entire period of
research work.
I thank Almighty God for helping me to complete
my work with success.
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