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STABILIZATION OF SUBGRADE USING GEOSYNTHETICS

Article in Journal of Advanced Research in Dynamical and Control Systems · January 2019

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 Journal of Advanced Research in Dynamical and Control Systems Vol. 12. Sp– 02 / 2019

STABILIZATION OF SUBGRADE USING GEOSYNTHETICS

1
G.G. Janakiraman, 2 P. Paramaguru, 3 T. Pratheep.,
1,2,3
PG scholar, Assistant Professor, Assistant Professor, 1Department of Environmental Engineering, 2,3Department
of Biotechnology, Ponnaiyah Ramajayam Institute of Science and Technology, Thanjavur Tamilnadu, India
1
gjraman001@gmail.com, 3pratheeptp@gmail.com

ABSTRACT

Soil stabilization is the progression which involves enhancing the substantial properties of the
soil in order to develop its strength, durability etc. by blending or mixing with additives. The
dissimilar forms of technique used for soil stabilization are: Soil stabilization with cement, Soil
stabilization with lime, Soil stabilization victimization hydrocarbon, and Chemical stabilization
associated an innovative promising experience of stabilization by Geo textiles and Geo artificial
fibers. Geotextiles have been effectively used for reinforcement of soils to recover the bearing
capacity. Roads are arteries of a city and an increase in population increases traffic. Heavy traffic
demands strong, smooth, durable and well maintained road pavement and hence healthy and
strengthened road network is essential for socioeconomic development of a country.
Reinforcement of road pavement using various materials is in practice, geosynthetics being
popular among them. Geosynthetics are synthetic products used to stabilize terrain. The focus of
this project is on better understanding of natural and artificial Geotextiles for strengthening of
sub grade soil. This project gives effect of reinforcement of Geotextiles on sub grade soil.
Laboratory California bearing ratio (CBR) tests were performed to examine the load-penetration
performance of reinforced granular soils with geotextile. Samples of granular soil with diverse
grading are chosen and tested lacking reinforcement. The consequences of these tests
demonstrate that, bearing ratio of reinforced granular soils with geotextile increases.

Keywords: Soft soil, CBR value, geo-grids, reinforcement, Geotextile

I. INTRODUCTION

One of the preferred materials for construction of road embankments on soft sub grade soils
being coarse grained soils is presented. During the recent past utilization of geosynthetics has
been increased to improve bearing resistance of weaker sub grades. Previous researches

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addressed the problems due to soft sub grade in several ways and provided solutions namely
geosynthetics & coarse fill for construction on these soils insitu. However considering scarcity of
fill material and cost of project a viable alternative can be bulk utilization of locally available
weak soils. Neglecting structure complicatedness etc., effectual exploitation is probable in small
scale projects if engineering performance is enhanced. These improved soils can be used as fill
over soft sub grades and ads benefit in the form of cost reduction. The design and construction of
pavement is quite challengeable and problematic for engineers over weak soils. Due to the
presence of highly compressible clayey soils the life of the pavements often effected. In the
available literature Geo-grids are popular as inclusion/ reinforcement for improving engineering
performance. Thus adoption of alternative construction techniques through reinforcing enables
increase in pavement life. . In the present study performance of sub grade soil using geogrids is
studied on different sub grades with different Geosynthetic reinforcement.

Roads are arteries of a city and thus they constitute an integral part of a city. Lowermost layer of
a pavement is called sub grade and it usually consist of soil present at the site. Roads frequently
have to be constructing across this feeble and compressible soil. Whenever a road needs to be
built on such soil with low CBR value, settlement may take place during or after construction,
with serious consequence in the lifespan of the road. It is consequently a widespread perform to
allocate the traffic loads in order to reduce the pressure on the soil sub-grade. This is usually
done by placing a reinforcement layer. Use of Geo-synthetics serves as a explanation to these
troubles. Geo-synthetics increase the strength of sub-grade soil and modify some of its properties
so that strength and lifespan of the road is increased. The project provides an overview of the
current Geo-synthetics technologies and highlights the function that geo-textiles perform in
enhancing the performance and extending the service life of paved road.

II. RELATED WORKS

In [1] E.A. Subaida, S. Chandrakaran, N. Sankar et al presents The results of an experimental

study conducted to investigate the beneficial use of woven coir Geotextiles as reinforcing
material in a two-layer pavement section, are presented. Monotonic and frequent loads were
practical on reinforced and unreinforced laboratory roadway segment through a rigid rounded
plate. The effects of placement location and stiffness of geotextile on the presentation of
reinforced sections were investigated using two base course thicknesses and two types of woven
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coir Geotextiles. The investigation consequences designate that the inclusion of coir Geotextiles
improved the bearing capacity of thin sections. Placement of geotextile at the interface of the sub
grade and base course increased the load carrying capacity significantly at large deformations.
Considerable development in bearing capacity was experimental when coir geotextile was
located within the base route at all stage of deformations. The best possible placement position of
coir geotextile was originated to be within the base course at a depth of one-third of the plate
diameter below the surface.

In [2] Akolade,A.S And Olaniyan et al presents Highway construction is one of the main
engineering design and construction in civil engineering in many countries all over the world.
Existing revise have exposed that civil engineers attractive in highway construction have quite a
little challenges during road construction especially as it is related to the topography of the site,
inadequate sub grade soil and high water table, inspite of this challenges, the application of
geogrids as a geotechnical property is imperative to improve the sub grade of soils with soaked
condition. Soil samples were label (A, B& C) at haphazard. These samples were taken to the
Laboratory for experiments to recognize and establish the Grain size analysis, atterberg,
compaction and California bearing ratio by introduction the geo-grids at unreliable depths and in
single layer under soaked circumstances (48hrs) to determine the strength of the soil samples.

In [3] Charles Anum Adams, Nana Yaw Amofa, Richter Opoku – Boahen et al presents Geogrid
reinforcement is gaining acceptance as an effective way of improving on the properties of
naturally occurring soils for road pavement construction. In lots of steamy countries, weak
lateritic sub grades are common and often discarded after proof rolling during construction due
to deprived strength. The precise objectives of this research were to 1) Determine the effect of
strength of geogrid reinforcement material on the California Bearing Ratio of a sample of
relatively poor lateritic sub grade material under soaked and unsoaked conditions and 2)
Establish the effect of geogrid reinforced sub grade on the design thickness of low volume paved
roads. This was undertaking for two strengths of geogrid in both soaked and unsoaked
circumstances. The California Bearing Ratios of the soil–geogrid sub grade was used to
determine the pavement layer thicknesses for a low volume paved road using the Transport
Research Laboratory Road Note 31 method of pavement design.

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In [4] Charles A. Adams, Yaw Adubofour Tuffour , Samuel Kwofie et al presents The
mechanism for strength development when unbound soils are reinforced with geogrid is not well
understood. Research on geogrid reinforcement has tended to center mostly on humanizing the
property of the geogrid with little attention to the pressure of soil properties on geogrid
performance. This learning investigated the effects of plasticity index and gradation properties of
lateritic soils on strength enhancement within a soil-geogrid-reinforced compound for a
pavement. Three samples of soil with dissimilar plasticity and gradation were compacted and
hardened in strength with and without geogrid reinforcement. Reinforcement involved
incorporating one and two layers of geogrid into the sample at diverse depths within the
compacted sample height. The consequences indicated that as soil plasticity increased, the CBR
decreased.

In [5] Abhijith R.P et al presents an experimental study on the utilization of natural coir fibers on
unpaved roads. Coir fibres provide a reinforcement action to the sub grade soil. Coir fiber is a
natural material obtained from coconut husk which is commonly seen in India. Use of coir fibres
improves the sub grade soil strength. Coir fibers of varying length from 0.5 to 3cm and varying
percentage from 2 to 8 of total weight of soil were added with the soil and CBR test was
conducted. The consequences completed that introduction Geotextiles at two third deepness from
bottom position was seems to be more effective. The reinforcement action is necessary during
initial stage and later reinforcement action is obtained by the consolidation of sub grade soil.

III. PROPOSED PROCESS EXPLANATION

a) Soil Stabilization

Soil stabilization is a technique of humanizing soil properties by blending and integration other
materials. There are a range of soil stabilization methods and there are different materials used
for soil stabilization. The soil alleviate with cement is known as soil cement. The cementing
action is believed to be the consequence of chemical reactions of cement with siliceous soil
during hydration reaction. The significant factors affecting the soil-cement are scenery of soil
content, conditions of mixing, compaction, curing and admixtures used. The suitable amounts of
cement needed for different types of soils may be as follow: Gravels – 5 to 10%, Sands – 7 to
12%, Silts – 12 to 15%, and Clays – 12 – 20%. The quantity of cement for a compressive

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strength of 25 to 30 kg/cm2 should generally be satisfactory for tropical climate for soil
stabilization.

b) Analysis of Soils

Soils are created by the grouping of weathered rock materials with humus. We also recognize
that soils provisions water and nutrients to flora. Soils also defend and sanitize rain water, pests
and wildlife habitation. The country affluence is depending upon soils of that country. Soil
analysis and their classification are very critical because in the entire globe the types of the soils
are same, but their analysis results may vary from location to location depending on various
characteristics of soils. When examine the soils, we should believe the essential substantial,
organic and compound property of soils. Classification of Soils is one of the demanding areas in
data mining and machine learning, in classification of soils can be happening from the view point
of soils as a matter and soil as a resource

Separation

Fig Soil separation theory

Roadway distress or failure may occur when fines from the sub grade contaminate an overlying
granular layer. High stresses transmitted from wheel loads on the surface above, combined with a
thaw weakened/saturated sub grade, typically because a base and sub grade to mix. This mixing
causes a reduction in the effective base thickness by reducing the actual modulus of the granular
base as well as its physical thickness. Due to wheel loads above, mixing occurs. Mixing is best
pictured as granular material pushed down into the soft sub grade and/or soft sub grade pumped
up into the overlying granular layer

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c) Classification Process

Soil classification scheme is indispensable for the identification of soil properties. Expert system
can be a extremely influential tool in identifying soils quickly and accurately. Traditional
classification systems include use of tables, flow-charts. Classification and prediction are two
forms of data analysis that can be used to extract models describing important data classes or to
predict upcoming data trends. It is a method in which a model learns to predict a class label from
a set of training data which can then be used to predict discrete class labels on novel samples.
The classification of soil was considered critical to revise because depending upon the fertility
class of the soil the domain knowledge experts determines which crops should be taken on that
exacting soil and which fertilizers should be used for the identical. To exploit the predictive
accuracy obtained by the classification replica when classifying examples in the test set
unnoticed during training is one of the chief goals of classification algorithm

Sub grade Soil

Sub grade is the lowermost layer of a pavement and it usually consists of soil already present at
site. This compressed sub grade might be the in-situ soil or a layer of chosen material. Sub
grades are commonly compacted before the construction of pavement. The load-bearing strength
of sub grade is deliberate by California Bearing Ratio (CBR) test. The long-term interaction
between a fine soil sub grade and granular layer, under dynamic loads, is likely to cause pumping
erosion of the soil sub grade and penetration of the granular particle in to the soil sub grade,
giving rise to permanent deflections and eventually to failure. These problems can be avoided
by reinforcing with other materials like Geotextiles, geogrid, Geonets etc.

d) Geosynthetics

Geosynthetics are synthetic products used to stabilize terrain. They are usually polymeric
products used to resolve civil engineering troubles. This includes eight main product categories:
Geotextiles, geogrids, Geonets, Geomembranes, Geosynthetic clay liners, Geofoam, geocells and
geocomposits. The growth in their use worldwide for transportation application has been nothing
short of phenomenal. It consists of natural and artificial product that is used along with soil in
geo-technical and civil engineering constructions. The majority common utilize of geo-synthetics
is in road construction. Geosynthetics increase the strength of sub grade soil and modify some of

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its properties so that the strength and lifespan of the road is increased. Main purposes of
Geosynthetic are Filtration, Separation, Drainage, Barrier, Reinforcement, Protection etc.

Reinforcement-Soil interaction mechanism

One of the beneficial effects of Geosynthetic reinforcement at the interface between base course
and sub grade soil is to carry the shear stresses induced by vehicular loads at the interface. The
geogrids have an elastic-plastic performance so that they rapidly react to applied loads with an
augment in the elastic modulus; in the case of short expression collision loading, creep
occurrence does not occur, therefore the whole tensile resistance of the geogrid can be mobilized.
Further, geogrids permit an augment of the dynamic dumping characteristics of the reinforced
soil evaluate to unreinforced soil, both through the energy that is directly engrossed by the
geogrid itself and due to friction generate in the active stage.

e) CBR test

Fig.3 Position of the geogrid in CBR mould

CBR tests are conducted on soil sample in lab with and without geo-grid. Single layer of geogrid
is placed at mid height of soil in mould for all the tests on geo-grid reinforced specimens.
Samples are compacted in CBR mould maintaining moisture and density at optimum conditions
determined in compaction test. To increase the interaction between soil and geogrid the
reinforcement material was embedded in thin layer of sand. CBR tests are carried out on all the
unreinforced soil and reinforced soil in both unsoaked and soaked conditions. CBR test (soaked)
is conducted on the samples after soaking for 96 hours (4 days). Prior to conduct of test the bulk
density, γ and moisture content, ω are determined. The test is repeated with varying geo-grids
and soil type.

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Fig. 4 Preparation of the reinforced soil sample for CBR test

Procedure for conduct of field CBR

Field CBR tests were conducted on soil fill reinforced with geogrid in test pits. Test pits of size
0.5m×0.5m×0.5m are excavated and filled with the soil maintaining moisture ω and density γ. In
order to ensure density and moisture after filling, core cutter tests are carried out on filled soil.
The density and moisture content in field γ0 and ω0 are recorded. CBR tests were conducted on
soil fill with and without geogrid. A single layer of geogrid is placed at mid height of soil in pit
for all the tests on geo-grid reinforced soil beds. The test is repeated with varying geo-grid and
soil fill. The load is applied using reaction loading technique supported by truck is taken

Fig Field test

The typical CBR test was chosen, so that a comparative analysis between the current test and
earlier test results without the use of Geosynthetic can be interpret. Furthermore, the geotextile
thickness and boundary effect can have authority on the concluding product, but any change of in
condition, will make it complicated for comparative analyses. Therefore the existing values can
be treated additional as comparative measurements. It is to be noted that the choice of the CBR

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test equipment as the testing platform brings some inherent troubles into the experimental study.
Small dimension of the CBR test equipment limits the size of the geotextile sheet.

f) Reinforcement

The conception of reinforcing deprived soil has sustained until the present day. Soil is strong in
compression but weak in anxiety. Reinforcement which has elevated tensile strength could be
effectual in counteracting materials which are feeble in tension. Reinforcement in sub grade is
done by introduction of a geotextile, geogrid or geocomposits which are good in tension into a
soil which is good in compression.

Reinforcement Methodology

The aim of doing this work is to highlight the employ of geosynthetics for humanizing the
strength and stability of sub grade soil. A Geosynthetic material can be natural or synthetic and
are added to soil to amplify its performance. It is establish that totaling of Geosynthetic augment
the stability of roads where behavior capacity of soil is low. Geosynthetic resources are frame
into textile, raft, mat, cell and membrane. Modern Geosynthetic material doesn’t usually decay
under biological and chemical processes which is useful in construction of road and its
maintenance.

Fig 8: Reinforcement materials

Basic laboratory tests such as standard proctor test, California Bearing Ratio test(CBR),
Unconfined Compression test, subdivision size determination, Direct shear test and Permeability
test were conducted on the collected sample to determine index and engineering properties of
soil. Five dissimilar Geotextiles were used for the present examination, as shown in figure 1.To
enumerate the improvement in engineering property of soil by placement of geotextile, tests were

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conducted on reinforced soil. Result then compared with result from basic soil. CBR analyses
were conduct with single layer and twice layer reinforcement. The material is providing at one
third and two third intensity of the mould such that it is about one and half times the distance of
the plunger. Direct shear investigation were conduct by solitary layer of reinforcement at center
of the mould perpendicular to the direction of shear

IV. CONCLUSION

When soil reinforced with geosynthetics it develop into stronger and stiffer than soil without
reinforcement. Placing of geotextile material in soil improves bearing capacity and load carrying
capacity of soil and thus augment service existence of pavement. Experimental studies show
increase in sub grade strength which support the theoretical studies carried out. Geosynthetics
when used in pavements perform different functions like reinforcement, separation, drainage and
filtration. Geotechnical test were accepted out to decide Grain size analysis, atterberg,
compaction and California bearing ratio test. CBR test were approved out by insertion the geo-
grids at varying depths and in solitary layer under unsoaked conditions to conclude the strength
of the soil. The consequence shows that the strength of sub grade is significantly increased by
introducing geo-grids reinforcement in the soil. It is establish that geo-grids placed at 3/5 the
distance from the base showed superior CBR value than when placed at 2/5 and 4/5 distances
from the base. The differences in the behavior of the soil under unsoaked conditions develop on
increasing the number of layers of geo-grids. As a sub grade stabilizer it has shown great effect
of improvement. It has short preservation, corrosion resistance and augments the service life of
road pavement. Geo-grids should be employed as a modernized form of improving road
construction on poor sub grade materials.

REFERENCE

[1] Abhijith R.P, “Effect of Natural Coir fibres on CBR Strength of Soil Subgrade”, International
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