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Improvement of Flexible Pavement With Use of Geogrid
Article · January 2011
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Improvement of Flexible Pavement
With Use of Geogrid
Sarika B. Dhule
Grad. Student, Master of Engineering, (Civil - Soil)
Government College of Engineering, Aurangabad (M.S), India
e-mail: sarika.sarkate2@gmail.com
S.S. Valunjkar
Professor, Department of Civil Engineering
Government College of Engineering, Karad (M.S), India
e-mail: ss valunjkar@yahoo.co.in
S.D. Sarkate
Associate Professor, Department of Mathematics, Milind College of
Science, Aurangabad (M.S), India; e-mail: sdsarkate@gmail.com
S.S. Korrane
Lecturer in Civil Engineering Department, Government College of
Engg. Aurangabad, (M.S) India
ABSTRACT
Weaker soils are generally clayey and expansive in nature which are having lesser strength
characteristics. Technique of improving the soil with geogrid increase the stiffness and load carrying
capacity of the soil through fractional interaction between the soil and geogrid material improving
black cotton soil. The load coming on the road crust is transferred to the underlying soil. If the soil
supporting the road crust is weaker, the crust thickness of road increases, which leads to the more cost
of construction. To achieve the economy and for proper performance of road, it is necessary to
improve the soil. In the present work locally available sub-grade soil of the road is modified by
addition of geotextile material in different percentage i.e.1%, 2% and 2.5% and 3% respectively.
Similarly geogrid is been used for improvement in properties of soft murum has also been studied.
Also geogrid is used in mix of soil and 2% cement in different proportion to study its effects. With
these attempts it will be possible to find out optimum mixes which are to be used for further
construction to achieve desired stability and economy in construction. For this purpose different test
were performed i.e sieve analysis, liquid limit, Plastic limit, Standard proctor test to find its maximum
water content and maximum dry density, specific gravity, Laboratory Unsoaked CBR and Laboratory
soaked CBR test to find it resistance to penetration. For different percentage of geogrid with soil,
murum and murum and cement economical cost analysis was carried out. Most economical mix with
geogrid is suggested from this study.
KEYWORDS:
Flexible Pavement, Geogrid, Unsoaked CBR.
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Vol. 16 [2011], Bund. C
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INTRODUCTION
Geogrids used within a pavement system perform two of the primary functions of Geosynthetics:
separation and reinforcements. Due to the large aperture size associated with most commercial geogrid
products, geogrids are typically not used for achieving separation of dissimilar material. The ability of a
geogrid to separate two material is a function of the gradations of the two material and is generally
outside the specifications for typical pavement materials. However, geogrids can theoretically provide
some measure of separation, albeit limited. For this reason , separation is a secondary function of geogrids
used in pavements. The primary function of geogrids used pavements in reinforcement, in which the
geogrid mechanically improves the engineering properties of the pavement system. The reinforcement
mechanisms associated with geogrids.
The three primary uses of a geogrid in a pavement system are to –
a. Serve as a construction aid over soft subgrades
b. Improve or extend the pavements projected service life, and
c. Reduce the structural cross section for a given service life.
d. To study the different aspects, regarding changes in properties of soil, murum and murum with
100gm cement due to mixing in different proportion of geotextile in it, soil and soft murum
samples were collected from the different location from Aurangabad city. The Properties obtained
by conducting laboratory tests are presented below.
e. Soil and Murum used in the experimentation is locally available from Aurangbad city, in
Maharastra State. The properties obtained by conducting laboratory tests are given below.
MATERIALS USED
Soil
Table 1: Engineering Properties of Soil and Murum.
Sr.No.
1
2
3
Particulars
Specific Gravity
Liquid Limit percent
Plastic Limit percent
Optimum Moisture Content
percent
Soil
2.32
71.13
27.9
Murrum
2.6
30
Non Plastic
25
14.5
5
Maximum Dry Density gm/cc
1.40
1.72
6
California Bearing Ratio
-Unsoaked percent
-Soaked percent
3.02
2.06
6.5
3.33
4
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Vol. 16 [2011], Bund. C
271
Reinforcement
The geotextile used in the present study is of high strength polyester geogrids patented by Kolon
International Corporation, Korea as Kologrid. The properties of Kologrid are as obtained from the
manufacturer are given below.
The properties of Kologrid are as follows.
Table 2: Specifications of Kologrids
Property/Item
Unit
Material
KGR 40
KGR 60
KGR 80
PET
PET
PET
Weight
g/m2
280
320
370
Aperture Size
mm +/–5%
20/22
20/20
20/20
Tensile Strength
@ 5% strain
@ break
kN/m
21/8
60/30
28/8
80/30
Elongation
Percent
< 12
<12
<12
Creep
Percent
<1
<1
<1
Roll Width
m
2.0
2.0
2.0
Roll Length
m
50
50
50
14/6
40/20
SAMPLE PREPARATION
Geogrid reinforced sample with soil, murum and murum with addition of cement were prepared at
maximum dry density, γdmax and optimum moisture content obtained by conducting Standard proctor test
on unreinforced soil. Samples were prepared by adding geogrid by 1 percent, 2 percent, 2.5 percent and 3
percent by weight of soil.
The amount of soil and geogrid required to fill standard mould at dry density was worked out and
water was added. Geogrids were placed in layers in layers in soil. In moist soil mix geogrid was
transferred to the mould in three layers and compaction was carried out using tamping of successive
layers to achieve a fairly uniform density throughout the depth of the sample.
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Vol. 16 [2011], Bund. C
272
SELECTION OF TESTS
When soil is used in pavement construction, in addition to strength, it should have good bonding
properties. To examine the possibility of using geogrid to improve strength of soil in pavement, various
laboratory tests were carried out. As a compaction test, Standard Proctor test is carried out which gives
the values of Maximum Dry Density (MDD) and Optimum Moisture Contents (OMC), for which samples
are prepared for testing. The CBR test gives the CBR values of the soil specimen, which is required for
the pavement design. Rather basic tests as Sieve Analysis, Liquid Limit Test, and Plastic Limit Tests were
performed.
Characteristics of material used
Characteristics of soil and murum are given in table 3. Values of OMC and MDD are found by
conducting standard proctor test. Depending upon the values of sieve analysis soil is classified as coarse
grained soil and murum is classified as non plastic.
Table 3: Basic characteristics of soil and murum
Soil
Specific
Gravity
SG
2.32
Liquid
limit
LL%
71.13
Plastic
Limit PL
%
27.9
Murrum
2.6
30
Non plastic
Description
OMC
%
MDD
gm/cc
CBR
25
1.6
2.06
14.5
1.72
3.33
Characteristics of soil with geogrid
Standard proctor test and laboratory soaked and unsoaked test are conducted on the soil with the
inclusion of 1 percent, 2 percent, 2.5 percent, 3 percent of geogrid by weight of soil sample.
Geotechnical Properties of Soil with Addition of Geogrid
The C.B.R. values of the soil, murum and murum with cement are given below in the following
table without and with geotextile.
Table 4: CBR for unsoaked and soaked soil and Murum.
Property
Unsoaked
Soaked
Soil
3.02
2.067
Murum
6.5
3.33
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Table 5: Effect of Geogrid on C.B.R for unsoaked and soaked soil
Property
Unsoaked
Soaked
Soil :1 percent geogrid
4.77
3.18
Soil :2 percent geogrid
6.36
3.498
Soil :2.5 percent geogrid
7.473
4.293
Soil :3 percent geogrid
8.904
4.293
Table 6: Effect of Geogrid on C.B.R for unsoaked and soaked Murum
Property
Unsoaked
Soaked
Murrum :1 percent geogrid
6.36
7.791
Murrum :2 percent geogrid
8.26
9.38
Murrum:2.5 percent geogrid
11.28
10.97
Murrum :3 percent geogrid
11.44
9.38
Table 7: Effect of Geogrid on C.B.R for unsoaked and soaked Murum
and 2 percent cement
Property
Unsoaked
Soaked
Murrum+Cement : 1 percent geogrid
50.88
45.69
Murrum+Cement : 2 percent geogrid
53.106
46.80
Murrum+Cement : 2.5 percent geogrid
53.901
46.60
Murrum+Cement :3 percent geogrid
54.06
45.90
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Vol. 16 [2011], Bund. C
274
1.65
3
Density gm/cm
1.60
1.55
1.50
1.45
1.40
1.35
1.30
15.2
18.5
25.0
26.8
2 7.2
Optimum MoistureContent (%)
Figure 1: OMC and MDD for Soil.
1.72
3
Density gm/cm
1.74
1.70
1.68
1.66
1.64
1.62
1.60
11.2
13.1
14.5
13.9
Optimum MoistureContent (%)
Figure 2: OMC and MDD for Murum
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Vol. 16 [2011], Bund. C
275
10.00
CBR
8.00
6.00
4.00
2.00
0.00
1.0
2.0
2.5
3.0
Percentage of Geogrid (%)
Figure 3: Unsoaked CBR for soil
5.00
CBR
4.00
3.00
2.00
1.00
0.00
1.0
2.0
2.5
3.0
Percentage of Geogrid (%)
Figure 4: Soaked CBR for soil
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Vol. 16 [2011], Bund. C
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CBR
15.00
10.00
5.00
0.00
1.0
2.0 6.36
2.5
3.0
Percentage of Geogrid (%)
Figure 5: Unsoaked CBR for Murum
CBR
15.00
10.00
5.00
0.00
1.0
2.0
6.36
2.5
3.0
Percentage of Geogrid (%)
Figure 6: Soaked CBR for Murum
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Vol. 16 [2011], Bund. C
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CBR
47.00
46.50
46.00
45.50
45.00
1.0
2.0 6.36
2.5
3.0
Percentage of Geogrid (%)
Figure 7: Unsoaked CBR for Murum and 2% Cement.
CBR
56.00
54.00
52.00
50.00
48.00
1.0
2.0 6.36
2.5
3.0
Percentage of Geogrid (%)
Figure 8: Unsoaked CBR for Murum and 2% Cement.
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Vol. 16 [2011], Bund. C
278
Figure 9: Placement of Geogrid in Pavement.
DISCUSSION
The results of the test are discussed here with. An attempt is made to know the causes for the change
in different characteristics of soil due to addition of varying percentages of geogrid in the soil. The
properties of soil with and without reinforcement are given below.
Compaction Characteristics
The optimum moisture content (OMC) of the soil is 25 and that of murum is14.5. The maximum dry
density of soil is 1.408 and that of murum is 1.72.
CONCLUSION
The results of the test are discussed here with. The attempt is made to know the causes for the
change in different characteristics of soil due to addition of varying percentages of geogrid in the soil. The
properties of soil with and without reinforcement are given below.
•
The optimum moisture content (OMC) of the soil is 25 and that of murum is 14.5. The maximum
dry density of soil is 1.6 and that of murum is 1.72. The customary dry density versus water
content Figures are plotted to obtain these values.
•
The Figures between geogrid content and CBR values are given in Figs. 3 to 8. From the results it
can be seen that the CBR values increase with the addition of geotextile when compacted for
constant density. The purpose of compaction is to improve the quality of the soil used as a
subgrade material for roads. The important properties are high shear strength, low permeability
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Vol. 16 [2011], Bund. C
279
and little tendency to settle under repeated loading. The maximum compaction is possible at the
OMC and MDD of the soil. Therefore, test of OMC and MDD serve as guide and basis to get the
maximum compaction in the field.
•
The CBR value for Unsoaked soil is 3.02 and with addition of 1 percent geogrid is 4.77, 2 percent
geogrid is 6.36, 2.5 percent geogrid is 7.473 and 3 percent geogrid is 8.904.
•
The CBR value for Unsoaked Murum is 6.5 and with addition of 1 percent geogrid is 6.36, 2
percent geogrid is 8.26, 2.5 percent geogrid is 11.28 and 3 percent geogrid is 11.44. The CBR
value for Unsoaked Murum is 3.33 and with addition of 1 percent geogrid is 7.791, 2 percent
geogrid is 9.38, 2.5 percent geogrid is 10.97 and 3 percent geogrid is 9.38.
•
The effect of geogrid on CBR for Unsoaked murum and 2 percent geogrid is cement with
addition of 1 percent geogrid is 50.88, 2 percent geogrid is 53.106, 2.5 percent geogrid is 53.901
and 3 percent geogrid is 54.06.
•
The effect of geogrid on CBR for Soaked murum and 2 percent geogrid is cement with addition
of 1 percent geogrid is 45.69, 2 percent geogrid is 46.80, 2.5 percent geogrid is 46.60 and 3
percent geogrid is 45.90.
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