study on improvement of sub grade soil using soil ... · abstract cement concrete pavement a...

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 7 (2018) pp. 126-134

© Research India Publications. http://www.ripublication.com

126

Study on Improvement of Sub Grade Soil using

Soil-Reinforcement Technique

Niteen Keerthi

Assistant Professor, Department of Highway Technology,

Visvesvaraya Technological University, Centre for PG Studies & Regional Office,

Kusnoor Road, Kalaburagi, India.

Sharanabasappa Kori

Assistant Professor, Department of Highway Technology,

Visvesvaraya Technological University, Centre for PG Studies & Regional Office,

Kusnoor Road, Kalaburagi, India.

Abstract

A pavement constructed over a weak subgrade soil needs

greater crust thickness due to low sub grade strength and such

pavements which are laid directly on the weak clayey soils

also fail early due to a non-uniform settlement resulting from

the volume changes of the weak sub grade soil in the presence

of moisture. Using geogrid a geo-synthetic material as

reinforcement in the soil is also another technique for

improving the sub grade strength. The choice of stabilizer

depends on the type of sub grade soil, type of soil

improvement required and accessibility of stabilizer.

Improvement in the strength characteristics of the sub grade

soil was evaluated using the CBR test. In the present study,

use of geogrid at the different position of the CBR mould did

not show good improvements in the strength of the black

cotton soil. This may be due to lack of friction between the

geogrid material placed and the black cotton soil. In case of

the Sandy gravel soil, the CBR strength increased in the range

of 6.8% to 10.2%, which is comparatively a better

improvement compared to the strength gain in the Black

cotton soil. This is because of good friction between the

geogrid material and the sandy gravel soil.

Keywords: CBR strength, geogrid, stabilizer and weak sub

grade soil.

Introduction

General

Earthwork comprises about 30% of the total

construction cost. A road crust or a pavement structure rests

over a prepared sub grade soil and thus it gains the required

strength from it. Sub grade soil is the foundation of a road

crust which gives considerable strength and supports the

whole pavement structure. The properties of the sub grade soil

should posses’ adequate stability under any climatic and

loading conditions during the design of the pavement. So, an

appropriate design and construction is the key to the effective

performance of a pavement. It has been observed that most of

the pavement distresses such as rutting, shoving, corrugation

and the experience of pumping, blowing etc., in case of

cement concrete pavement are mainly due to the weak sub

grade beneath the pavement structure. Hence, the preparation

of properly compacted sub grade is an important activity

which has to be carried out in any of the road construction

works [1].

Objectives of the present study

To improve the strength of soil using geogrid

reinforcement and study the optimum position of the

reinforcement resulting in maximum strength.

To study and compare the performance of the

conventional soil and reinforced soil.

The scope of the present study

The present study is limited to compare the basic

properties and the performance of the conventional soil

and the soil modified by using geogrid reinforcing layer

within the soil specimen.

To achieve the defined objective of the study, physical

and strength performance tests were performed in the

laboratory on two types of soils viz., Black cotton soil

and Sandy gravel soil before and after the modification.

Also, the optimal position of Geogrid for improvement

of strength characteristic of soil was determined during

soaked CBR test.

Literature review

General

Geogrid is one of the geo-synthetic materials, used to enhance

the performance of sub grade soil by creating a composite

soil/Geogrid structure. Geo-synthetic material is used to

reinforce RE walls and also used in reinforcing the road sub

soils or sub base. The geogrid is effective in tension, whereas

the soil gets to pull out under tension. Usually, Geogrid is

made of polymer material, such as polyethylene or

polypropylene, polyvinyl alcohol and polyester.



127

Jute geo-textile and geogrid were used as a soil-

reinforcement: This paper describes result of a decrease in the expansion ratio

and increases in the CBR value as the layer of reinforcement

was increased. Geogrid reinforced soil showed a better result

than a geotextile reinforced soil. In case of both Jute geo-

textile and geogrid, there was further decrease in swelling [1].

The optimum position of geogrid in reinforcing the soil

was determined by CBR test:

This paper aimed to improve the engineering properties of

locally available clayey soil by soil reinforcement technique

by placing geogrid in different stages. In the study, the

geogrid was placed at different positions with respect to the

height of the specimen. The various positions of

reinforcement selected during the study were 20%, 40%, 60%

and 80% of the height of the specimen in CBR mould. It has

been observed that reinforcing the soil at 0.2H from top of the

specimen in CBR mould showed an improvement in CBR

value by 324%.

A Methodology of the present study

General

In the present study two soils, Black cotton soil and sandy

gravel soil were used in this study.

To assess the index properties and compaction properties

of the two soils.

To determine the change in strength properties of the

unreinforced and reinforced soil specimen by CBR after 4

days soaking.

To determine the optimum position of the geogrid placed

in CBR mould with respect to the maximum strength of

the soil.

Methodology:

A brief layout plan of methodology carried out during

this study is been illustrated in the below flowchart.

A Material used for the present study:

Black cotton soil - procured from laboratory stock of

RASTA which was brought from Gulbarga District.

As per IS soil classification this soil was classified as

inorganic clays (CH).

Sandy gravel soil - procured from laboratory stock

of RASTA which was brought from Jigani Industrial

Area, Anekal, and Bangalore district. As per IS soil

classification this soil was classified as Sandy Clays

(SC).

Geogrid - Biaxial polyester Geogrid was sourced

from Reno Agro and Engg Pvt. Ltd. Coimbatore

manufacturer and supplier. The properties of the

Geogrid is as shown in the table 1 below.

Table 1: Properties of Geogrid material

Property Grid specification

Material composition Polyester

Mesh aperture size (mm) 18x18

Thickness (mm) 2

Tensile Strength (kN/M) Wrap-

Wise

100

Tensile Strength (kN/M) Across-

Wrap

100

Mass Per Unit,>g/Sqm 450

Elongation (%) 15

Coating (%) 20

Rolling Width (m) 2.5

Rolling Length (m) 50

Figure 1: Appearance of geogrid material cut in a circular

disc of the diameter slightly less than the diameter of

Compaction/CBR mould.

Experimental investigations on soil using geogrid as soil

reinforcement: During this method of stabilization, all the basic laboratory

tests were conducted on the soils and strength test i.e. CBR

was tested on unreinforced and reinforced soil specimens.

The following laboratory tests were conducted on BC soil and

sandy gravel soil

1. Grain size analysis.

2. Atterberg limits.

3. Modified Compaction Test.



128

4. Soaked CBR Test (with and without geogrid). -

Expansion ratio

Grain size analysis: Wet sieve analysis was conducted on BC soil and sandy

gravel soil as per IS 2720 (Part IV) - 1985. Wet sieve

analysis results are tabulated in table 2. The particle size

distribution curve of Black cotton soil and Sandy gravel soil

is shown in graph 1.

Figure 2: Wet sieve analysis of Black cotton soil and Sandy

gravel soil.

Consistency Limits and Indices:

Atterberg limits test which includes liquid limit and

plastic limit test is carried out on BC soil and sandy

gravel soil as per IS 2720 – Part V - 1985. Liquid limit,

plastic limit and plasticity index results for BC soil and

Sandy gravel soil are tabulated in table 3 and Liquid

limits of both soils are shown in graph 2.

Figure 3: Casagrande’s apparatus, soil sample and tools

Figure 4: Liquid limit tests of Black cotton soil and

Sandy gravel soil

Figure 5: Plastic limit test of Black cotton soil.

Compaction Test – Heavy compaction:

Modified compaction test was carried out on black cotton

soil and sandy gravel soil as per the standard procedure

mentioned in IS-2720 (Part VIII):1983. The MDD and

OMC results for Black cotton soil and Sandy gravel soil

are tabulated in table 4 and the compaction curves are

shown in graph 3 and graph 4.

Soaked CBR Test:

Native soils (Without geogrid): CBR test was conducted

on BC soil and sandy gravel soil as per the code

specification IS 2720 Part XVI - 1987. The soil

specimens were soaked for 4days prior to testing.

The Soil reinforced using geogrid: The CBR test was

also conducted on the soil specimen reinforced using

geogrid at different positions from top of the specimen in

CBR mould at 20%, 40%, 60% and 80%. The soil-

reinforced specimens were also moist cured for 4-days

before testing.

Procedure: Firstly, the material was

weighed for preparation of

the soil specimen and the

obtained Optimum

Moisture Content was

added to the soil.

The CBR mould was placed

on a solid base plate with

extension collar attached.

The soil mixture was

divided into five parts and

soil was placed into the

CBR mould.

The soil was placed in 5 layers and each layer was

compacted by giving 56 blows each from 4.89 kg of

rammer with a free fall of 450mm.

Geogrid was placed above a compacted layer

depending on the choice of position; it may be 20%,

40%, 60% and 80%.

For example, at 40% position, the geogrid was placed

at 76.38 mm from the top and 98.62mm from the

bottom of the specimen in CBR mould respectively

as shown in figure 3.6.



129

Typical position of geogrid placed in CBR mould is

as shown in figure 3.7.

The CBR moulds were kept for 4-days soaking.

The same method has been followed for all other

positions.

Figure 6: A typical position of geogrid placed at 40%

height of specimen in CBR mould.

Figure 7: A typical position of geogrid material placed into

the CBR mould

Figure 8: Extracted CBR soil specimens of Black cotton

soil and sandy gravel reinforced by geogrid

Expansion Ratio: The initial height of the soil placed in the CBR mould

was noted down.

The dial gauges were fixed to the CBR mould as

shown in figure 3.9. Then the initial dial gauge

reading (di) was noted down.

The set up was maintained undisturbed for 96 hours

and the readings were noted down each day.

Till 4-days of soaking a constant water level should

be maintained.

Final dial gauge readings were recorded after 4-days

of soaking (df).

Expansion ratio calculation,

Figure 3.9: Expansion-measuring test set up

𝐄𝐱𝐩𝐚𝐧𝐬𝐢𝐨𝐧 𝐑𝐚𝐭𝐢𝐨 =𝐝𝐟 − 𝐝𝐢

𝐡∗ 𝟏𝟎𝟎

Where,

di - Initial reading of dial gauge in mm.

df - Final reading of dial gauge after 4 daysof soaking in mm.

h - Initial height of the soil specimen in mm.

Results and Data analysis

Wet sieve analysis of black cotton soil & sandy gravel soil:

Table 2 Wet sieve analysis results

Soil

fractions

Particle size

distribution

Black

cotton

soil

Sandy

gravel

soil

Gravel

(%)

4.0 17.0

Sand (%)

7.2 46.0

Silt and

Clay

(%)

88.8 37.0



130

Graph 1: Grain size distributions of Black cotton soil and

Sandy gravel soil

Atterberg Limits for Black cotton soil and Sandy

gravel soil:

Table 3 Atterberg limits test results

Soil type Tests Results Plasticity

Index

Black cotton

soil

Liquid Limit 65.2 %

26.3 %

Plastic Limit 38.9 %

Sandy gravel

soil

Liquid Limit 32.8 %

11.7 %

Plastic Limit 21.1 %

Graph 2: Liquid limits of Black cotton soil and Sandy

gravel soil

Modified Compaction test for Black Cotton Soil and

Sandy gravel Soil:

Table 4 Compaction test results

Type of soil Black cotton

soil

Sandy gravel

soil

MDD, gm/cm3 1.63 2.08

OMC, % 20.6 9.8

Graph 3: Compaction curve of Black cotton soil

Graph 4: Compaction curve of Sandy gravel soil

Soaked CBR Test (with and without geogrid) for Black

Cotton soil:

Table 5: CBR test results of BC soil with and without

reinforcement

Serial

No.

The position of reinforcement with

respect to the height of the specimen.

CBR

(%)

1. Without reinforcement 1.3

2. Geogrid at 20% 2.0




30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

0.01 0.1 1 10

% P

ass

ing

Sieve size (mm)

Black

cotton soil

Sandy

gravel soil

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

0 20 40 60

Wa

ter C

on

ten

t (%

)

No. of Blows, N

Black cotton soil

Sandy gravel soil

1.612

1.624

1.608

1.563

1.540

1.560

1.580

1.600

1.620

18.00 20.00 22.00 24.00 26.00D

ry D

en

sity

, g/

cc

Moisture Content (%)

2.031

2.067

2.026

2.002

1.960

1.980

2.000

2.020

2.040

2.060

2.080

8.00 9.00 10.00 11.00 12.00 13.00

Dry

De

nsi

ty,

g/cc

Moisture Content (%)



131

Graph 5: CBR curves of BC Soil with and without

reinforcement

Soaked CBR Test (with and without geogrid) for Sandy

gravel soil:

Table 6: CBR test results of BC soil with and without

reinforcement

Serial

No.

The position of reinforcement with


CBR

(%)

1. Without reinforcement 6.8





Graph 6 CBR curves of Sandy gravel Soil with and

without reinforcement

Expansion Ratio (with and without geogrid) for Black

Cotton soil:

Table 7: Expansion ratios of unreinforced and

reinforced BC soil

The position of Reinforcement with


Swelling

%

Without reinforcement 15.7

Geogrid at 20% 9.5

Geogrid at 40% 7.4

Geogrid at 60% 10.4

Geogrid at 80% 11.5

Discussion and conclusions

CBR for Black Cotton Soil-Reinforced using geogrid:

Graph 7: Variation in the strength of Black cotton soil

with respect to the geogrid position

From graph 7 CBR strength of conventional BC soil

without any reinforcement is 1.3%.

About 54% increase in CBR value after the BC soil

reinforced using geogrid at 0.2H from top of the

specimen.



specimen



specimen



specimen.

0.003.006.009.00

12.0015.0018.0021.0024.0027.0030.0033.0036.0039.0042.00

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Lo

ad

(k

g)

Deformation (mm)

Without geogrid

GEOGRID @20%

GEOGRID @40%

GEOGRID @60%

GEOGRID @80%

0

50

100

150

200

250

300

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Lo

ad

, k

gs

Penetration, mm

1.3

2.0 2.11.9 1.8

0

0.5

1

1.5

2

2.5

0 20 40 60 80 100

CB

R V

alu

e (%

)

Geogrid position from top of the

specimen(%)

CBR Chart)



132

CBR for Sandy Gravel Soil-Reinforced using

geogrid:

Graph 8: Variation in the strength of Sandy gravel

soil with respect to geogrid position.

From graph 8 CBR value of conventional Sandy

gravel soil without any reinforcement is 6.8%.

About 40% increase in CBR value after the Sandy

gravel soil reinforced using geogrid at 0.2H from top

of the specimen.



of the specimen.



of the specimen.



of the specimen.

It can be observed that the CBR value of Sandy

gravel soil increased from 6.8% to 10.2% at a 0.4H

position and which is comparatively a better

improvement compared to the strength gain in the

black cotton soil. This position is considered as an

optimum position.

This is because of a greater internal friction between

the geogrid and the soil particles of sandy gravel soil

as compared to clayey soil.

Expansion Ratio for Black Cotton soil (with and without

geogrid) :

Graph 9: Variation in swelling property of Black cotton

soil with respect to the geogrid position

The above chart represents the effect of reinforcement on

swelling of BC soil.

The native soil showed a swelling of 15.7%, it is

mainly due to the expansive nature of the BC soil.

When BC soil was reinforced using geogrid, it was

observed that the swelling potential was reduced

substantially and increased thereafter.

From graph 9 expansion ratio of BC soil without

reinforcement is 15.7%.

From graph 9 expansion ratio of BC soil reinforced

using geogrid at 0.2H from top of the specimen is

9.5%, geogrid at a 0.2H position has 40% lesser

expansion ratio than conventional BC soil




expansion ratio than conventional BC soil.









6.8

9.5 10.2

7.2 7.0

0

2

4

6

8

10

12

0 20 40 60 80 100CB

R V

alu

e (%

)

Geogrid position from top of the

specimen (%)

CBR Chart

15.7

9.57.4

10.411.5

0

5

10

15

20

0 20 40 60 80Sw

elli

ng

Ra

tio

, %

Geogrid position from top of the specimen

(%)

Expansion Ratio Chart



133

.Table 8: Consolidated Results

Properties Black cotton soil Sandy gravel soil

Wet Sieve Analysis

%

Gravel

4.0 17.0

%Sand 6.2 46.0

%Silt and Clay 88.8 37.0

Atterberg Limits Test

L.L (%) 65.2 32.8

P.L (%) 38.9 21.1

P.I (%) 26.3 11.7

Modified Compaction Test

MDD (g/cc) 1.63 2.08

OMC (%) 20.3 9.8

CBR TEST (with and without reinforcement)

- 0.2H 0.4H 0.6H 0.8H - 0.2H 0.4H 0.6H 0.8H

Soaked CBR (%) 1.3 2.0 2.1 1.9 1.8 6.8 9.5 10.2 7.2 70

Swelling (%) 15.7 9.5 7.4 10.4 11.5 -

Properties Black cotton soil Sandy gravel soil

Wet Sieve Analysis

%

Gravel

4.0 17.0

%Sand 6.2 46.0

%Silt and Clay 88.8 37.0

Atterberg Limits Test

L.L (%) 65.2 32.8

P.L (%) 38.9 21.1

P.I (%) 26.3 11.7

Modified Compaction Test

MDD (g/cc) 1.63 2.08

OMC (%) 20.3 9.8

CBR TEST (with and without reinforcement)

- 0.2H 0.4H 0.6H 0.8H - 0.2H 0.4H 0.6H 0.8H

Soaked CBR (%) 1.3 2.0 2.1 1.9 1.8 6.8 9.5 10.2 7.2 70

Swelling (%) 15.7 9.5 7.4 10.4 11.5 -

Conclusions :

From the above discussions made, the following can be

concluded:

1. Using geogrid as soil-reinforcement, there was no

significant improvement of reinforced Black cotton

soil compared to the reinforced sandy gravel soil

because there is no internal friction between grain to

grain and between soil and geogrid material.

2. It is observed that the swelling of BC soil was

affected as it was reinforced in various positions, at

40% position the swelling was decreased by 8.3%

compared to swelling potential of conventional BC

soil.

3. The strength of sandy gravel soil in terms of CBR is

6.8%. When sandy gravel was reinforced using geo-

grid at 40 %, the CBR value increased to 10.12 %.

This stage is considered as the optimum stage in

improving the CBR strength.

4. Due to a good internal friction between the geo-grid

material and the soil particles of sandy gravel soil it

showed a good increase in the CBR value of the

sandy gravel soil.

5. Therefore, geogrid a polymeric material can be used

as a reinforcing material into the subgrade soils for

improving the strength performance of that soil.

Future Scope:

1) Conducting plate load test with geo-grid in the

black cotton soil in a different stage to

determine the performance of sub-grade soil.

2) Upon attaining the required strength of weak

subgrade soil by reinforcing, the cost analysis

has to be done and the availability of the

suppliers has to be checked. 3) The satisfaction that accompanies the successful

completion of any task would be incomplete without

the mention of the people who made it possible,

whose constant guidance and encouragement

crowned our efforts with success.

References

[1] A K Choudhary, K S Gill and J N Jha,

Improvement in CBR values of expansive soil

sub-grades using geo-synthetics, Indian

Geotechnical Conference (J-233) December-

2011,15-1.

[2] Pradeep Singh, K S Gill, CBR Improvement of

clayey soil with Geo-grid Reinforcement,

International Journal of Emerging Technology

and Advanced Engineering (IJETAE), (Vol2,

Issue 6,) June 2012.

[3] Evangelin Ramani Sujatha, Improving the

strength of sub-grade using geogrid.

International Journal Of Core Engineering &

Management (IJCEM)Volume 1, Issue 4 (2012)

[4] Carotti and Rimoldi, A Nonlinear Model for the

Seismic Response Analysis of Geosynthetic

Reinforced Soil Structures, Geosynthetic

International Journal, 5(1-2): 167-201 (1998)

[5] B C Punmia, Soil mechanics and

foundationLaxmi publications.16th edition:

9-142.

[6] S. K. Khanna, C. E. G. Justo and A.

Veeraragavan, Highway materials and

pavement testing, Nem Chand & Bros, Fifth

edition, 2013.

[7] IS 2720 Part IV (1985), “Indian Standard

method of test for Soil, Grain size Analysis”



134

(Second Revision), Bureau of Indian

Standards, New Delhi.

[8] IS 2720 Part V (1985), “Indian Standard method

of test for Soil, Determination of Liquid Limit,

Plastic Limit” (Second Revision), Bureau of

Indian Standards. New Delhi.

[9] IS 2720 Part XVI (1987), “Indian Standard

method of test for Soil, Determination of CBR”

(Second Revision), Bureau of Indian Standards.

New Delhi.

[10] IS 2720 Part VIII (1983), “Indian Standard

method of test for Soil, Determination of Water

content and Dry Density relation using Heavy

Compaction” (Second Revision), Bureau of

Indian Standards. New Delhi.

study on improvement of sub grade soil using soil ... · abstract cement concrete pavement a...

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