IGC 50 INDIAN GEOTECHNICAL CONFERENCE - Guru …igs/ldh/files/igc 2015 pune/THEME 2... · · 2017-05-14th INDIAN GEOTECHNICAL CONFERENCE 17th ... Rahul Joshi, Assistant Prof., Department

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INDIAN GEOTECHNICAL CONFERENCE

17th

– 19th

DECEMBER 2015, Pune, Maharashtra, India

Venue: College of Engineering (Estd. 1854), Pune, India

IMPROVEMENT OF ENGINEERING PROPERTIES OF BLACK COTTON

SOIL BY STABILISATION USING STPS SLUDGE, LIME AND METAL

POWDER

Ashish Ghanmode1, Pravin Sakhare

2, Rahul Joshi

3, Ajitkumar Kumbhar

4,

Milinda Mahajan5, H. B. Dhonde

6

ABSTRACT

Black Cotton Soils (BCSs) are one of the major soil deposits in India. BCSs are seldom used to

support buildings or pavements owing to their treacherous and unreliable behaviour. Generally,

BCS has very low bearing capacity, and high swelling and shrinkage characteristics. Swelling

pressure is a major cause of failure in foundations supported by BCS. Moreover, saturated BCS

have lower bearing capacity and higher degree of compressibility resulting in settlements, and

subsequently leading to failure. However, the lack of space and resources make it necessary to

build structures supported on BCS. Therefore, usually the most practical and feasible option left

is to improve the characteristics of the BCS by stabilisation.

The main objective of soil stabilisation is to improve the performance of soil by increasing its

strength, stiffness, stability and durability by suitable application of mechanical energy or

chemical admixtures, or combination of these methods. Stabilisation of BCS by using industrial

by-product wastes such as pre-treated Sewage Treatment Plant Sludge (STPS) and filler non-

hazardous Metal Powder (MP) along with the conventionally used Lime (L) stabiliser, could be a

practical and sustainable option. The paper presents test results and optimisation laboratory study

of stabilised BCS using L blended with industrial reused STPS and MP, targeted to enhance the

engineering characteristics (i.e. Unconfined Compressive Strength, UCS and California Bearing

Ratio, CBR value) of unstable BCS. Due care must be taken to ascertain that the industrial waste

products used for soil stabilisation are free of any hazardous materials that may contaminate the

ground.

The BSC sampled from site was mixed with L, STPS and MP in varying percentage i.e. 0% to

10%, 0% to 40%, and 0% to 5% by weights, respectively; thus forming either binary or ternary

blends of stabilised BCS. The aim of the investigation was to examine the effects of stabilizers

and admixtures on various geotechnical properties of the BCS. Laboratory UCS and CBR tests

were conducted on the stabilized BCS samples. From experimental studies it was found that the

Ashish Ghanmode, Pravin Sakhare, Rahul Joshi, Ajitkumar Kumbhar,Milinda Mahajan and H.B. Dhonde

maximum increase in strength of the mono-blend stabilised BCS (BCS+L) was at 10% by weight

of L dosage. A steady increase in UCS and stiffness of binary-blends of stabilised BCS

(BCS+STPS+L) with increasing amount of STPS was observed. Optimum STPS and L dosage

was found to be 30% and 10% by weight, respectively; with a maximum percentage increase in

UCS of about 98%.

Further, UCS tests were conducted on the binary-blends of treated BSC with ternary addition of

MP and with partial replacement of L. A significant influence of MP on the UCS and stiffness of

ternary-blend relative to the binary-blends of treated BCS was observed. The ternary-blends of

treated BCS were found to be over three and six times stronger than that of the binary and virgin

BCS samples, respectively - considering the UCS values. The optimal STPS, L and MP dosage

were found to be 30%, 5%, and 5% by weight, respectively; with a maximum percentage

increase in UCS of about 547% over the virgin BCS. Hence, MP can partly yet effectively

replace the comparatively pricy lime when ternary blends (STPS+L+MP) are used to stabilise

BCS. More encouraging CBR results of the binary- and ternary-blends were obtained. CBR tests

on untreated and various blends of treated BCS clearly indicate the enhanced performance of

ternary-blends over the binary-blends of stabilised BCS. Even very small dosage (≈ 5% by

weight) of MP were found to reinforce the soil more effectively than other stabilisers. The study

indicate a significant enhancement in the engineering performance of waste-stabilised BCS.

Keywords: Black cotton soil, soil stabilisation, lime, STPS sludge, metal powder, unconfined

compressive strength, California bearing ratio

_________________

1Mr. A. Ghanmode, Under-graduate Student, Department of Civil Engg., VIIT, Pune, India, [email protected]

2Er. P. S. Sakhare, Assistant Prof., Department of Civil Engg., VIIT, Pune, India, [email protected]

3Er. R. A. Joshi, Assistant Prof., Department of Civil Engg., VIIT, Pune, India, [email protected]

4Er.Ajitkumar Kumbhar, Manager, MVML, Chakan, India, [email protected]

5Dr. Milinda Mahajan, Associate Prof., Department of Civil Engg., VIIT, Pune, India, [email protected]

6Dr. H. B. Dhonde, Associate Prof., Department of Civil Engg., VIIT, Pune, India, [email protected]

UCS of untreated and treated BC soil –

60%BSC+30%STP+5%Lime+5%Metal Powder

Untreated

Treated (BSC+STP+L+MP)

CBR test specimens of treated BC soil

UCS test specimens of treated BC soil

mailto:[email protected]






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IMPROVEMENT OF ENGINEERING PROPERTIES OF BLACK

COTTON SOIL BY STABILISATION USING STPS SLUDGE, LIME AND

METAL POWDER

Ashish Ghanmode, UG Student, Department of Civil Engg., VIIT, Pune, India, [email protected]

Pravin Sakhare, Assistant Prof., Department of Civil Engg., VIIT, Pune, India, [email protected]

Rahul Joshi, Assistant Prof., Department of Civil Engg., VIIT, Pune, India, [email protected]

Ajitkumar Kumbhar, Manager, MVML, Chakan, India, [email protected]

Milinda Mahajan, Associate Prof., Department of Civil Engg., VIIT, Pune, India, [email protected]

H. B. Dhonde, Associate Prof., Department of Civil Engg., VIIT, Pune, India, [email protected]

ABSTRACT: Black Cotton Soils (BCS) are seldom used to support buildings or pavements owing to

their treacherous behaviour. This paper highlights the stabilisation of BCS using pre-treated Sewage

Treatment Plant (STPS) sludge and filler metal powder as industrial wastes, in proportion with lime as a

cementitious material. The effects of blended reused industrial waste (STPS sludge and metal powder)

and lime on engineering properties of stabilised BCS viz. Unconfined Compressive Strength (UCS) and

California Bearing Ratio (CBR) are discussed. The study indicate a significant increase in UCS and CBR

values of waste-stabilised BCS.

Keywords: Black cotton soil, soil stabilisation, lime, STPS sludge, metal powder, unconfined

compressive strength, California bearing ratio

INTRODUCTION

The physical properties of Black Cotton Soil

(BCS) vary from place to place. At liquid

limit, the volume change is of the order of

200% to 300% and results in swelling

pressure as high as 8 kg/cm2 to 10 kg/cm

2

[1]. Generally, BCS has very low bearing

capacity and high swelling and shrinkage

characteristics. Water lubricates the soil

particles and makes the inter-particle

mechanical interlock unstable. Swelling

pressure is a major cause of failure in

foundations supported by BCS. Moreover,

saturated BCS have lower bearing capacity

and higher degree of compressibility,

ultimately resulting in settlements. A

number of failures of earth dams, tunnels,

hydraulic structure, foundations and road

embankments have occurred due to swelling

problems of these soils [2]. However, the

lack of space, resources and other related

issues make it necessary to build structures

supported on BCS. Therefore, usually the

most practical and feasible option left is to

improve the characteristics of the BCS by

stabilisation.

Stabilisation of BCS by using industrial by-

product wastes such as post-treated Sewage








Treatment Plant Sludge (STPS) and filler

non-hazardous Metal Powder (MP) along

with the conventionally used lime stabiliser,

could be a practical and sustainable option.

Very few studies have been done on this

important topic. The paper presents test

results and optimisation study of stabilised

BCS using lime blended with industrial

reused STPS and MP, target to enhance the

engineering characteristics (i.e. Unconfined

Compressive Strength, U.C.S. and

California Bearing Ratio, CBR value) of

unstable BCS. Due care must be taken to

ascertain that the industrial waste products

used for soil stabilisation are free of any

hazardous materials that may contaminate

the ground.

Soil Stabilisation It is the process by which a stabilising agent

is added to natural soil deposit to improve

the engineering properties of the soil by

mechanical or chemical means or both [2,3].

The main objective of stabilisation is to

improve the performance of a material by

increasing its strength, stiffness, stability and

durability. The performance should be at

least equal to, if not better than that of a

good quality natural material [3]. There are

many types of stabilizer that can be used,

each with their own advantages and

disadvantages. The type and quantity of

stabilizer added depends mainly on the

strength and performance that needs to be

achieved. The addition of even small

amounts of stabilizer, for example up to 2

per cent cement, can modify the properties

of a material [3].

Sub-base Characteristics

The sub-base is an important layer in both

flexible and rigid pavements. It mainly acts

as a structural layer helping to spread the

wheel loads so that the subgrade is not

overstressed. It can also act as a drainage

layer. The selection of material and the

design of the sub-base will depend upon the

particular design function of the layer and

also the expected in-situ moisture conditions

[4,5]. Stabilized sub-bases can be used for

both flexible and rigid road pavements,

although the reasons for doing this can vary.

In order to identify the benefits of stabilizing

sub-bases, it is necessary to examine the role

of the sub-base for each pavement type [5].

A stabilized, and therefore stiffer, sub-base

provides greater load spreading ability and

hence reduces stresses imposed on the

subgrade. When stabilized, the sub-base

provides much of the structural rigidity in

the pavement, and also assists during the

compaction of the upper granular layers and

hence increases their ability to withstand

deformation [5]. If the sub-base is stabilized,

reflection cracking in an asphalt surface

layer can be minimized by having an

unbound granular road base. This unbound

road base provides not only a large

proportion of the structural load spreading

but also assists in delaying or preventing

reflection cracking from the shrinkage and

movement of the stabilized layer, enabling

longer service life.

MATERIALS AND METHODOLOGY

Materials

The experimental work was conducted with

in-situ BCS at Mahindra Vehicle

Manufacturing Ltd. (MVML), Pune, India;

post-treated bio-waste STPS collected from

an onsite secondary treatment plant, non-

hazardous solid waste MP from the plant,

and lime as stabilizer.

STPS

Sludge originates from the process of

treatment of organic and inorganic waste

water. Due to the physio-chemical processes

involved in the treatment, the sludge tends to

concentrate heavy metals and poorly

biodegradable organic compounds as well as

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potentially pathogenic organisms (viruses,

bacteria etc.) present in waste waters. Most

wastewater treatment processes produce a

sludge which has to be appropriately

disposed-off. In this work, the reuse of post-

treated STPS with properties as shown in

Table 1 was carried out with other blend-

materials for stabilisation of BCS. The pre-

treated STPS was deemed suitable to be

safely disposed-off in local grounds.

Table 1 Properties of treated STPS sludge

Properties Activated

Sludge

BOD (mg/l) 11

COD (mg/l) 27

Suspended Solids (mg/l) 13

pH (unit) 7.6

Total Dissolved Solids (mg/l) 940

Boron (B), (mg/l) 0.7

Alkalinity-CaCO3 (mg/l) 226

Total Hardness-CaCO3 (mg/l) 265

BOD–Biological Oxygen Demand COD–Chemical Oxygen Demand

Lime (L)

Lime provides a relatively economical way

of soil stabilisation. Lime modification

effects an increase in strength brought by

cation exchange capacity rather than

cementing effect brought by pozzolanic

reaction [6]. Lime particles transform the

flocculating platy clay particles into

interlocking needle-like stable and stronger

structure. Lime stabilisation effect may

partly be due to pozzolanic reaction in which

pozzolana materials reacts with lime in

presence of water to produce cementitious

Ca-Si-hydrate compounds, the effect can be

brought by either quicklime, CaO or

hydrated lime, Ca(OH)2;

Ca(OH)2 + Soil Silicates Ca-Si-hydrate (cementitious C-H-S)

The lime additions that are usually applied

in soil solidification are up to 12% by

weight, which are quite low yet effective [6,

7].

MP

Metal waste left over from manufacturing

and consumptions, such as parts of vehicles

building supplies, and surplus materials, are

in the form of small pieces or threads, and

are discarded by-products. Usually, large

amount of metal waste is generated and

available locally. Metal waste from the

workshop in the form of powder is used for

strengthening or filler material. In this work,

the researchers have uniquely used the MP

from MVML plant as a filler and

strengthening agent blended with STPS and

lime to stabilise BCS.

PROPERTIES OF BC SOIL

The physical and engineering properties of

BCS at MVML site are presented in Table 2.

Table 2 Properties of untreated BCS

The BCS was classified as silty-clay with

high plasticity (MH-CH) and designated (as

relatively weak soil of poor bearing strength,

as affirmed by the UCS and CBR tests)

with a medium degree of expansion and

marginal degree of severity with regards to

swelling pressure [9].

Characteristics [8] Value

Specific Gravity 2.8

Liquid Limit (%) 72

Plastic Limit (%) 34

Maximum Dry Density (kg/cm3) 1.4

Optimum Moisture Content (%) 20

Unconfined Compression Strength

(UCS) (kg/cm2)

1.0

California Bearing Ratio (CBR) (%) 4.2


Procedure of Mixing

Initially, the soil was air dried and hand

sorted to remove the pebbles and vegetable

matter, if any. It was then oven dried,

ground, pulverized and sieved through a

600μ sieve. The soil was then mixed

thoroughly with lime in varying percentage

i.e. 0% to 10% by weights and tested to

determine their physical and engineering

properties. After that BCS was mixed with

10% lime and stabilized with STPS. The

STPS was mixed with BCS in varying

percentages, i.e. 0% to 40% by weight. BCS

stabilised with lime and STPS was also

tested with and without MP in different

dosages of 0% to 5%, by weight.

The aim of the investigation was to examine

the effect of mixing and stabilizers on

various geotechnical properties of BCS.

Following laboratory tests were performed

to study the geotechnical properties of BCS

before and after mixing;

Specific gravity

Atterberg’s Limits

Standard Proctor test

UCS test

CBR test

Initially, tests were conducted on BCS and

lime to find out the appropriate proportion of

lime addition. From experimental studies it

was found that the maximum increase in

strength of the mono-blend stabilised BCS

was at 10% by weight lime dosage.

LABORATORY TEST RESULTS

UCS of cohesive soils is commonly used to

estimate the shear strength of that soil. UCS

load-deformation plot for the untreated BCS

is shown in Fig. 1. From the plot it can be

seen that the cohesive soil suddenly fails at a

strain level of about 7.0%. The photographs

of UCS test of untreated and stabilised BCS

samples is shown in Fig. 2 (a) and (b).

Addition of STPS and MP to BCS were

found to darken the colour.

Fig. 1 UCS of untreated BCS

(a) BCS

(b) UCS samples of treated BCS with MP

Sample 1: BCS-80%, STPS -10%, L-7%, MP-3%




Fig.2 UCS failed samples of treated BCS

Table 3 UCS of BCS blends without MP

BCS# STPS

Sludge# Lime#

(L)

UCS (qu)

kg/cm2

Shear Strength kg/cm2

% Increase

100 0 0 1.03 0.515 -

80 10 10 1.38 0.790 34

70 20 10 1.77 0.885 72

60 30 10 2.04 1.020 98

50 40 10 1.71 0.905 66 # - % by weight

Table 3 and Fig. 3 shows the UCS test

results of binary-blended BCS with STPS

and lime but without the MP. A steady

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increase in UCS with increasing amount of

STPS was observed. Optimum STPS and

lime dosage was found to be 30% and 10%

by weight, respectively; with a maximum

percentage increase in UCS of about 98%.

This corresponds to an increase in strength

from a medium-stiff to stiff BCS. It is to be

noted that these are laboratory tests that

represent ideal case. Fig. 3 depicts that the

stiffness of BCS blended with near optimum

amounts of STPS dosages, increases

significantly.

Fig. 3 UCS of BCS blends without MP

Further, UCS tests were conducted on the

binary-blends of treated BSC with ternary

addition of MP and with partial replacement

of lime. Table 4 shows the UCS results for

these ternary-blends of stabilised BCS.

Table 4 UCS of BC soil with MP

BCS#

STPS Sludge#

Lime#

(L)

Metal Powder#

(MP)

UCS (qu)

kg/cm2

Shear strength kg/cm2

% Increase

100 0 0 0 1.03 0.515 -

80 10 7 3 2.63 1.315 155

70 20 6 4 4.09 2.045 297

60 30 5 5 6.66 3.33 547

50 40 5 5 3.24 1.62 215 # - % by weight

The UCS test results of untreated and

ternary-blends of stabilised BCS samples are

shown in Figures 4 to 7. A significant

influence of MP on the UCS and stiffness of

ternary-blend relative to the binary-blends of

treated BCS was observed.

Fig. 4 UCS of untreated and treated BCS (80%BSC+10%STPS+7%L+3%MP)

Fig. 5 UCS of untreated and treated BCS

(70%BSC+20%STPS+6%L+4%MP)


Untreated

Treated (BSC+STPS+L+MP)

Untreated


Untreated




The ternary-blends of treated BCS were

found to be over three and six times stronger

than that of the binary and virgin BCS

samples, respectively considering the UCS

values. Fig. 8 depicts the comparision of

these results. The optimal STPS, L and MP

dosage was found to be 30%, 5%, and 5%

by weight, respectively; with a maximum

percentage increase in UCS of about 547%

over the virgin BCS. This corresponds to an

increase in strength from a medium-stiff to a

very-stiff BCS. Hence, MP can partly yet

effectively replace the comparatively pricy

lime when ternary blended with STPS are

used to stabilise BCS.

Fig. 8 UCS of BCS with and without MP

CBR Test Results

CBR test is an empirical penetration test for

assessing relative and not the absolute

strength of subgrade material [10]. The

punching shear under CBR test condition

does not in any way represent the stress

regime on the subgrade under a flexible

pavement due to traffic wheel loads [11].

However, CBR tests are most commonly

adopted to provide an indicative and relative

strength estimate of various soils.




Fig. 9 CBR test samples of treated BCS

Table 5 CBR test results of BCS

Sample (BCS- STPS-L-MP)

% wt.

CBR Value (%)

for Penetration

%Increase

in CBR

Value 2.5mm 5mm

100-BCS 4.30 4.32 0

70-20-10-0 22.03 21.49 412

60-30-10-0 24.80 22.97 460

50-40-10-0 10.12 9.95 135

70-20-6-4 27.98 25.23 551

60-30-5-5 31.23 30.21 626

50-40-5-5 29.50 28.90 586

Photographs of CBR test on treated BCS

samples are shown in Fig. 9. Table 5 shows

the results of CBR tests on untreated and

various blends of treated BCS (Fig. 10 and

11). The CBR test results clearly indicate the

enhanced performance of ternary-blends

over the binary-blends of stabilised BCS.

Untreated


1 2 3

Ratio,

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Fig. 10 CBR of treated BCS

(BCS+STPS+L)

Fig. 11 CBR of treated BCS

(BCS+STPS+L+MP)

The optimal binary- and ternary-blends of

STPS, L and MP dosage were found to be

30%, 10%, and 30%, 5% and 5% by weight,

respectively; with a maximum percentage

increase in CBR value for the binary- and

ternary-blends of about 460% and 626%,

respectively over the virgin BCS. Hence,

even small amounts of MP dosages (≈ 5%

by weight) can effectively replace lime in

ternary blended STPS are used to stabilise

BCS.

CONCLUSIONS

The study presents the following

conclusions based on limited laboratory

experimental study on stabilisation of BCS

by mono (BSC+L), binary (BSC+L+STPS)

and ternary (BSC+L+STPS+MP) blends of

non-hazardous industrial waste by-products.

Strength performances of the stabilised BCS

were established by UCS and CBR tests.

It is imperative to ascertain that the

industrial waste products to be used for

soil stabilisation are free of any hazardous

materials that may contaminate the ground

in actual application.

The maximum increase in UCS of mono-

blend stabilised BCS (BCS+L) was at 10%

by weight of L-dosage.

A steady increase in UCS and stiffness of

binary-blended BCS (BCS+STPS+L) with

increasing amount of STPS was observed.

Optimum STPS and L dosage was found

to be 30% and 10% by weight,

respectively; with about two-fold increase

in UCS over untreated BCS. This

corresponds to an increase in strength from

a medium-stiff to a stiff BCS.

A significant influence of MP on the UCS

and stiffness of ternary-blends

(BCS+STPS+L+MP) relative to the

binary-blends of BCS was observed. The

ternary-blends of treated BCS were found

to be over three and six times stronger than

that of the binary and virgin BCS samples,

respectively; considering the UCS values.

The optimal STPS, L and MP dosage were

found to be 30%, 5%, and 5% by weight,

respectively; with a maximum percentage

increase in UCS of about 547% over the

virgin BCS. This corresponds to an

increase in strength from a medium-stiff to

Untreated

Treated (BSC+STPS+L)

Treated (BSC+STPS+L)

Untreated



a very-stiff BCS. Hence, MP can partly yet

effectively replace the comparatively pricy

lime when ternary blends (STPS+L+MP)

are used to stabilise BCS.

Encouraging CBR results of the binary-

and ternary-blends were obtained. CBR

tests on untreated and various blends of

treated BCS clearly indicate the enhanced

performance of ternary-blends over the

binary-blends of stabilised BCS. Even

very small dosage (≈ 5% by weight) of MP

were found to reinforce the soil more

effectively than other stabilisers.

The study indicate a significant

enhancement in the engineering

performance of waste-stabilised BCS.

Overall it can be concluded that partial

replacement of virgin BCS with ternary

blend of lime (L), industrial wastes -

sludge (STPS) and discarded metal

powder (MP), can be potentially effective

for ground improvement in infrastructure

projects on BCS.

Extended work of this study is planned for

an in-situ application of the optimal binary

and ternary blends of industrial wastes for

stabilisation of BCS.

REFERENCES

1. Sivapullaiah, P. V. (2013), Use of Solid

Waste to Enhance Properties of

Problematic Soils of Karnataka,

Research Report, IISC, Bangalore, India.

2. Chen, F. H. (1988), Foundations on

expansive soils, Chen & Associates,

Elsevier Publications, USA.

3. Bowles, J. (1988), Foundation Analysis

and Design, 4th Ed., McGraw-Hill

Publishing Company, USA.

4. Terzaghi, K., Peck, R. B. and Mesri, G.

(1996), Soil mechanics in engineering

practice, 3rd

Ed., John Wiley, New York,

USA.

5. TRL (1993), A guide to the structural

design of bitumen-surfaced roads in

tropical and sub-tropical countries,

ORN-31, 4th

Ed., ODA-DOT,

Transportation Research Laboratory,

UK.

6. Mitchell, J. K. (1993), Fundamentals of

soil behaviour, 2nd

Ed., John Wiley, New

York, USA.

7. Patel, A. V. (2011), Study of

geotechnical properties of black cotton

soil contaminated by castor oil and

stabilisation of contaminated soil by

sawdust, National Conference on

Recent Trends in Engineering &

Technology, 13-14th

May, 2011, B.V.M.

Eng. College, Gujarat, India.

8. IS 2720 (Reaff. Multi-years), Methods of

test for soil – Parts: I, V,VII, X, & XVI,

Bureau of Indian Standards, New Delhi,

India.

9. IS 1498-1970 (Reaff. 2007),

Classification and identification of soils

for general engineering purposes, 8th

Reprint, Bureau of Indian Standards,

New Delhi, India.

10. Ranjan, G. and Rao, A.S.R. (2000),

Basic and Applied Soil Mechanics,

2nd

Ed., New Age International, New

Delhi, India.

11. Gulhati, S.K. and Datta, M. (2005),

Geotechnical Engineering, Tata

McGraw-Hill, New Delhi, India.

Documents

IGC 50 INDIAN GEOTECHNICAL CONFERENCE - Guru …igs/ldh/files/igc 2015 pune/THEME 2... · · 2017-05-14th INDIAN GEOTECHNICAL CONFERENCE 17th ... Rahul Joshi, Assistant Prof., Department