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5
0th
IGC
50th
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
5
0th
IGC
50th
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 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
Ashish Ghanmode, Pravin Sakhare, Rahul Joshi, Ajitkumar Kumbhar,Milinda Mahajan and H.B. Dhonde
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
5
0th
IGC
50th
INDIAN GEOTECHNICAL CONFERENCE
17th
– 19th
DECEMBER 2015, Pune, Maharashtra, India
Venue: College of Engineering (Estd. 1854), Pune, India
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
Ashish Ghanmode, Pravin Sakhare, Rahul Joshi, Ajitkumar Kumbhar,Milinda Mahajan and H.B. Dhonde
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%
Sample 2: BCS-70%, STPS -20%, L-6%, MP-4%
Sample 3: BCS-60%, STPS -30%, L-5%, MP-5%
Sample 4: BCS-50%, STPS -40%, L-5%, MP-5%
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
1 2 3 4
5
0th
IGC
50th
INDIAN GEOTECHNICAL CONFERENCE
17th
– 19th
DECEMBER 2015, Pune, Maharashtra, India
Venue: College of Engineering (Estd. 1854), Pune, India
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)
Fig. 6 UCS of untreated and treated BCS (60%BSC+30%STPS+5%L+5%MP)
Untreated
Treated (BSC+STPS+L+MP)
Untreated
Treated (BSC+STPS+L+MP)
Untreated
Treated (BSC+STPS+L+MP)
Ashish Ghanmode, Pravin Sakhare, Rahul Joshi, Ajitkumar Kumbhar,Milinda Mahajan and H.B. Dhonde
Fig. 7 UCS of untreated and treated BCS (50%BSC+40%STPS+5%L+5%MP)
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.
Sample 1: BCS-70%, STPS -20%, L-7%, MP-3%
Sample 2: BCS-60%, STPS -30%, L-5%, MP-5%
Sample 3: BCS-50%, STPS -40%, L-5%, MP-5%
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
Treated (BSC+STPS+L+MP)
1 2 3
Ratio,
5
0th
IGC
50th
INDIAN GEOTECHNICAL CONFERENCE
17th
– 19th
DECEMBER 2015, Pune, Maharashtra, India
Venue: College of Engineering (Estd. 1854), Pune, India
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
Treated (BSC+STPS+L+MP)
Ashish Ghanmode, Pravin Sakhare, Rahul Joshi, Ajitkumar Kumbhar,Milinda Mahajan and H.B. Dhonde
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.
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3. Bowles, J. (1988), Foundation Analysis
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4. Terzaghi, K., Peck, R. B. and Mesri, G.
(1996), Soil mechanics in engineering
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