A Study on the Compaction Characteristics and Stress ... · PDF filebehaviour of Kuttanad Clay Stabilized with Rice Husk Ash and Lime ... ABSTRACT Many construction ... in the manufacture

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com February 2016, Volume 4, Issue 2, ISSN 2349-4476

57 Mrs.Neenu M. B

A Study on the Compaction Characteristics and Stress-Strain

behaviour of Kuttanad Clay Stabilized with Rice Husk Ash

and Lime

Mrs. Neenu M. B

Asst.Professor ,Department of Civil Engineering

Muthoot Institute of Technology and Science, Puthencruez,Ernakulam,Kerala

ABSTRACT

Many construction sites are underlain by soils that are both weak and compressible.These include soft clays, highly

organic soils, and others. Such soils are often found near the mouth of the rivers, along the perimeter of bays, and

beneath wetlands. They are prone to shear failure and excessive settlements. Fortunately, engineers and contractors

have developed methods of coping with weak and compressible soils and have successfully built large structures,

highways, and other facilities on very poor sites. Soil stabilization methods continue to make considerable progress, both

quatitatively and qualitatively as a result of not only technology developments but also of an increasing awareness of the

environmental and economic advantages of modern ground improvement methods.The selection of the correct

stabilization method at an early stage in design can have an important effect on foundation choice and can often lead to

more economical solutions when compared to traditional approaches. Kuttanad clay is characterized by its high

compressibility and low shear strength which leads to a number of foundation problems. This paper presents the

effectiveness of combination of rice husk ash (RHA) and lime as stabilizing agents. RHA is pozzolanic in nature and is

produced from rice husk by burning it at a controlled temperature.The compaction characteristics of soil blended with

various percentages of rice husk ash and lime are studied. A series of undrained unconsolidated triaxial compression

tests are conducted under different confining pressures to investigate the stress- strain characteristics of Kuttanad clay

blended with RHA and lime. Various percentages of combination of RHA and lime are used in triaxial sample

preparation and thus the optimum percentage of combination is worked out. It is observed that the addition of RHA and

lime to Kuttanad clay alter its stress- strain response considerably.

KeywordsRice husk ash ,lime, Kuttanad clay

1. INTRODUCTION

Kuttanad is located in Alappuzha district of Kerala ,India.It is an agricultural area and is known for

underwater The clay in this region is dark grey colour and the dominant clay minerals are kaolinite and

illite.Kuttanad clay is characterized by its high compressibility and low shear strength .The low bearing

capacity of the soil has lead to foundation failures and embankment failures.The foundation recommended for

such area is raft or pile foundations but it is not economical.Thus the Kuttanad clay requires an effective and

economic method of stabilization. The use of lime to dry ,modify and stabilize soil is a well established

construction technique. If a soil does not possess reactive silica necessary to react with lime then materials

rich in silica can be added in the form of volcanic ashes, defatted diatomaceous earth,siliceousflyashes or any

other pozzolanic materials. These pozzolanic materials enhances the formation of cementitious and pozzolanic

gels [calcium silicate hydrate gel (CSH)and calcium aluminate silicate hydrate gel (CASH).Being relatively

inexpensive industrial by–products that are pozzolanic in nature is a good option for stabilizing soil. The

potential for using industrial by-products such as blast furnace slag, flyash ,Rice husk ash and cement kiln

dust for the stabilization of soil has been investigated. The use of these by-products in soil stabilization can

lead to low cost construction and can provide an envirornmental friendly means of their disposal.

Kerala produces 6.25 lakh tonns of rice annually. The 22% of the grain is husk which can be converted to

RHA . The RHA has a variety of uses.It is used as absorbent for oil and chemicals.RHA is used as insulation

powder in steel mills, in homes and refrigerants, in the manufacture of of refractory bricks. It is used as

release agent in the ceramics industry,as a pozzolan in cement and concrete industry. RHA is used as

repellants in the form of vinegar- tar. RHA can replace silica fume in high strength concrete. It is used as a

vulcanizing agent for ethylene – propylene- dieneterpolymer. The United States National Lime Association



58 Mrs.Neenu M. B

(2001) has listed the benefits of lime stabilization that includes plasticity reduction, , swell reduction

Improved stability, very substantial improvement in shear strength, ,continued strength gain with time and

long term durability over decades of services even under severe environmental condition. The effect of

organic content on the plasticity ,shear strength and compressibility characteristics of Kuttanad clay has been

investigated by SudheeshThiyyankadi and Shima Annex(2011).The test result indicate that the plasticity

characteristics increases with increase in organic content. The shear strength decreases and compression index

increases with the increase in organic content in the clay. The coefficient of primary consolidation was found

to decrease and rate of secondary compression was found to increase with increase in organic content.JBindhu

and AswathiRamabadhran (2011)conducted studies on the strength improvement of Kuttanad clay by the

addition of cement. Cement content ranging between 10%-30% was found effective and curing period resulted

in strength gain of soil.A detailed study was made on the effect of rice straw as a reinforcement material in

Kuttand clay by P.G Greeshma and Mariamma Joseph(2011).It was observed that the unconfined compressive

strength of soil reinforced with 0.5% untreated straw of random length was increased by 1.94 times with

respect that of unreinforced soil.Being the largest agricultural area in the state of Kerala, Kuttanad region

produces the large quantity of rice. Rice milling generates by-product known as husk. This surrounds the

paddy grain. During milling of paddy about 78% of weight is received as rice, broken rice and bran. Rest 22%

of the weight of paddy is received as husk. This husk is used as fuel in the rice mills to generate steam for the

boiling process. This husk contains about 75% organic volatile matter and the remaining 25% of the weight of

this husk is converted into ash during the firing process, known as Rice Husk Ash (RHA). This RHA in turn

contains around 85% - 90% amorphous silica. So for every 1000 kg of paddy milled, about 220 kg (22%) of

husk is produced, and when this husk is burnt in the boilers, about 55 kg (25%) of RHA is generated.

2. EXPERIMENTAL PROGRAMME

2.1 Materials

The soil used for the study is clay collected from Pulinkunnu region of Kuttanad in Alappuzha district. The

soil was partially air dried before the commencement of the experiments. Laboratory tests were performed on

the clay to determine the properties The properties of untreated clay are shown in Table1.Industrially

manufactured rice husk ash was purchased from N.K Enterprises, Jharsugdha.The physical properties and

chemical properties of rice husk ash is shown in Table2. The lime used for the study was locally available.

Table 1. Properties of Kuttanad Clay

Property Value

Specific gravity 2.36

Liquid Limit (%) 60

Plastic Limit (%) 30

Plasticity Index (%) 30

Shrinkage limit (%) 22

Clay (%) 31

Silt (%) 49

Sand (%) 20

Optimum Moisture content(%) 27.5

Maximum Dry density(g/cc) 1.36

Colour Dark Grey

Optimum lime content (%) 5



59 Mrs.Neenu M. B

Table 2.Physical Properties of Rice Husk Ash

Physical state Solid –Non hazardous

Appearance Fine Powder

Particle size 25 micron -mean

colour Grey

Odour Odourless

Specific Gravity 2.3

2.2 Combination scheme for stabilized soil mixture

A series of Standard Proctor tests and undrained unconsolidated triaxial tests were conducted on Kuttanad

clay with various combinations of the stabilizers, rice husk ash (RHA) and lime.A control specimen of

Kuttanad clay alone and a total of 16 combinations were studied.The mix proportions used in this study are

listed below:

Kuttanad clay only

Kuttanad clay and 5 % RHA and 2% / 4% / 6% / 8%&10% lime


Kuttanad clay and 15 % RHA and 2% / 4% / 6% / 8% &10% lime


2.3 Compaction tests

Compaction tests were conducted as specified in IS 2720 Part (VII) for determining the optimum moisture

content and maximum dry density of the soil. Each sample are prepared by hand mixing air dried soil passing

through 20mm IS sieve with the corresponding percentages of lime and RHA in a non porous metal tray in a

dry state.Thereafter mixing is carried out with the addition of water. Mixing is continued until water spreads

all over the soil forming a uniform mixture. The OMC and MDD for all the combinations are determined. The

water content was determined by oven drying method. Fig 1 gives the compaction characteristics of Kuttanad

clay blended with5%RHA and2%,4%,5%,6%,8%&10% lime.Table 3 gives the values of maximum dry

density and optimum moisture content for the other combinations.

Figure 1. Compaction curve for 5% RHA and 2%,4%,5%,6%,8% &10% lime

1.15

1.2

1.25

1.3

1.35

1.4

0 20 40 60

Ma

xim

um

dry

den

sity

(g/c

c)

Optimum Moisture Content %

5RHA2L

5RHA4L

5RHA6L

5RHA8L

5RHA10L



60 Mrs.Neenu M. B

Table 3.Variation of MDD(g/cc) and OMC(%)for different combinations of RHA and Lime with

Kuttanad Clay

RHA 10% 15% 20%

Lime MDD OMC MDD OMC MDD OMC

2% 1.3 31 1.282 31.35 1.265 31.55

4% 1.28 31.5 1.264 32.5 1.255 35..5

6% 1.276 35 1.229 35.7 1.204 38.77

8% 1.3 35.2 1.263 35.4 1.24 38.5

10% 1.32 35 1.287 35.2 1.26 38

2.4 Unconsolidated Undrained Triaxial Test without pore water measurement

The required weight of oven dry soil passing through 425µ was determined based on the dry unit weight water

content and volume of the specimen. The weight of the additives was also determined based on the percentage

content by dry weight of the soil. The soil specimen is prepared with the corresponding percentages of RHA

and lime at the optimum moisture content and maximum dry density. The specimen was prepared with the

static compaction method in a mould of 39mm diameter and 78mm length. The specimens were demolded 1

min after the completion of compaction. The test was conducted at a strain rate of 0.6mm/minute on three

identical specimen under cell pressures of 100 kN/m2 ,200 kN/m

2 and 300 kN/m

2

Figure.2, Figure.3F Figure.4 shows the effect of rice husk ash and lime on the stress - strain behaviour of

Kuttanad clay in undrained unconsolidated traxial tests at cell pressures of 100kN/ m2,200kN/ m

2 & 300kN/

m2respectively.

Figure.2aStress-strain curves of Kuttanad clay stabilized with 5%RHA and 2%4%6%8%&10%lime at a cell

pressure of 100kN/ m2

Figure.2b Stress-strain curves of Kuttanad clay stabilized with 10%RHA and 2%4%6%8%&10%lime

without at a cell pressure of 100kN/ m2

0

20

40

60

80

100

120

0 0.02 0.04 0.06 0.08 0.1

Dev

iato

r S

tres

s (k

N/m

2)

Strain

Untreated soil

5RHA2L

5RHA4L

5RHA6L

5RHA8L

5RHA10L

0

20

40

60

80

100

120

140

0 0.02 0.04 0.06 0.08

Dev

iato

r S

tres

s (k

N/m

2)

Strain

10RHA2L

10RHA4L

10RHA6L

10RHA8L

10RHA10L



61 Mrs.Neenu M. B

Figure.2c Stress-strain curves of Kuttanad clay stabilized with 15%RHA and 2%4%6%8%&10%lime


Figure.2d Stress-strain curves of Kuttanad clay stabilized with 20%RHA and 2%4%6%8%&10%lime


Figure.3a Stress-strain curves of Kuttanad clay stabilized with 10%RHA and 2%4%6%8%&10%lime


0

20

40

60

80

100

120

140

0 0.02 0.04 0.06 0.08Dev

iato

r S

tres

s (k

N/m

2)

Strain

15RHA2L

15RHA4L

15RHA6L

15RHA8L

15RHA10L

0

20

40

60

80

100

120

140

0 0.02 0.04 0.06 0.08

Dev

iato

r S

tres

s (k

N/m

2)

Strain

20RHA2L

20RHA4L

20RHA6L

20RHA8L

20RHA10L

0

20

40

60

80

100

120

140

160

180

0 0.02 0.04 0.06 0.08

Dev

iato

r S

tres

s (k

N/m

2)

Strain

Untreated soil

5RHA2L

5RHA4L

5RHA6L

5RHA8L

5RHA10L



62 Mrs.Neenu M. B




at a cell pressure of 200kN/ m2

Figure.3d Stress-strain curves of Kuttanad clay stabilized with 20%RHA and 2%4%6%8%&10%lime


0

50

100

150

200

0 0.02 0.04 0.06 0.08

Dev

iato

r S

tres

s (k

N/m

2)

Strain

10RHA2L

10RHA4L

10RHA6L

10RHA8L

10RHA10L

0

50

100

150

200

0 0.02 0.04 0.06 0.08 0.1

Dev

iato

r S

tres

s (k

N/m

2)

Strain

15RHA2L

15RHA4L

15RHA6L

15RHA8L

15RHA10L

0

50

100

150

200

0 0.02 0.04 0.06 0.08 0.1

Dev

iato

r S

tres

s (k

N/m

2)

Strain

20RHA2L

20RHA4L

20RHA6L

20RHA8L

20RHA10L



63 Mrs.Neenu M. B

Figure.4aStress-strain curves of Kuttanad clay stabilized with 5%RHA and 2%4%6%8%&10%lime






0

50

100

150

200

0 0.02 0.04 0.06 0.08 0.1Dev

iato

r S

tres

s (k

N/m

2)

Strain

Untreated soil

5RHA2L

5RHA4L

5RHA6L

5RHA8L

5RHA10L

0

50

100

150

200

0 0.02 0.04 0.06 0.08Dev

iato

r S

tres

s (k

N/m

2)

Strain

10RHA2L

10RHA4L

10RHA6L

10RHA8L

10RHA10L

0

50

100

150

200

0 0.02 0.04 0.06 0.08

Dev

iato

r S

tres

s (k

N/m

2)

Strain

15RHA2L

15RHA4L

15RHA6L

15RHA8L

15RHA10L



64 Mrs.Neenu M. B

Figure.4dStress-strain curves of Kuttanad clay stabilized with 20%RHA and 2%4%6%8%&10%lime


3. RESULTS AND DISCUSSION

3.1 Effect of RHA and lime on compaction characteristics

The MDD decreased with increase in the RHA and lime and correspondingly the OMC increased upto 6% of

lime. Beyond 6% lime there is an increase in MDD with only slight variation in OMC. The values of MDD

and OMC for different combinations are shown in Table 3With increase in lime content the electrolyte

concentration of the pore water increases leading to reduced thickness of double layer. As a result of which

the clay particles move closer and vendor walls attraction becomes predominant producing flocculation and

hence a card house type of clay structure. This card house structure of the clay matrix effectively resists the

compaction effort giving rise to lower density and higher moisture content. With further increase in lime

content the concentration of cations increases near to the negatively charged clay surfaces. This difference of

charged concentration leads to osmosis. Since the ions are under influence of charge on clay surface they are

restrained against diffusion, the water molecules diffuse towards clay surface to equalize charge concentration

. This leads to separation of clay particles that produces more dispersed soil structure, thereby permits the

particles to slide part over each other into a more oriented and denser matrix

Effect of RHA and lime on the stress - strain behavior of Kuttanad clay

The strength of Kuttanad clay improved with the addition of RHA and lime.The maximum strength was

obtained at 6% of lime for all percentages of RHA.The strength improved with increase in RHA upto

15%.This is because of the flocculation that occurs due to the cation exchange and the reaction that occur

between silica and alumina at the edges of the clay minerals.The cohesion intercept indicates the strength of

the clayey soil. The cohesion intercept of the Kuttanad clay increased with the increase in RHA content upto

15% . Beyond 15% RHA there is decrease in strength. This decrease in the cohesion intercept above 15%

RHA content may be due to extra RHA that could not be mobilized for the reaction which consequently

occupies spaces within the sample. This reduced the bond in the Kuttanad clay-RHA –lime mixture. Similarly

for all percentage of RHA content the cohesion intercept decreased with beyond 6%lime The c-value of

Kuttanad clay is obtained as 30 kN/m2 and it increased to a maximum value of 87.5 kN/m2 at 15%RHA and

6% lime .

0

20

40

60

80

100

120

140

160

180

0 0.02 0.04 0.06 0.08 0.1

Dev

iato

r S

tres

s (k

N/m

2)

Strain

20RHA2L

20RHA4L

20RHA6L

20RHA8L

20RHA10L



65 Mrs.Neenu M. B

4. CONCLUSIONS

The effectiveness of rice husk ash and lime on Kuttanad clay was analysed. The compaction behaviour and

the stress-strain behaviour of untreated Kuttanad clay and Kuttanad clay blended with lime and RHA was

studied.Thefollowing are the main conclusions.

1. The maximum dry density decreased with increase in lime upto 6% irrespective of rice husk ash

content.Beyond 6% lime there is an increase in maximum dry density.

2. The stress-strain behaviour of Kuttanad clay improved with the addition of RHA and lime .At 15% RHA

and 6% lime the deviator stress increased by 130%.

3. The c -value of Kuttand clay improved by 191% at 15%RHA and 6% lime without curing

REFERENCES [1]. IRC Highway Research Board (2000),State of the art: Lime –Soil Stabilization, Special Report 1,1-33.

[2] Alhassan .M(2008),Potentials of rice husk ash for soil stabilisation,Technical Report 11(4),246-250.

[3] Dr.R.M.Brooks(2009),Soil stabilisation with flyash and rice husk ash,International Journal of Research and

Reviews in Applied Sciences,1(3),209-217.

[4] D.R.Koteswara,P.R.T.,Pranav.&M.,Anusha.M(2011) Stabilisation of expansive soil with rice husk ash ,lime and

gypsum-an experimental study, IJEST 11(3)807-816.

[5] D.R.Koteswara, P.R.T.Pranav&Ganji .V(2012), A laboratory study on the efficacy of rice husk ash and potassium

chloride on the stabilization of expansive soil, IJEST 4(1), 97-108

[6] Mitchell, K.J. and Soga, K. (2005),Fundamentals of Soil Behaviour, 3rd edition, John Wiley and Sons, New York

Documents

A Study on the Compaction Characteristics and Stress ... · PDF filebehaviour of Kuttanad Clay Stabilized with Rice Husk Ash and Lime ... ABSTRACT Many construction ... in the manufacture