User manual | STRENGTH CHARACTERISTICS OF FIBRE REINFORCED COMPACTED POND ASH ALOK SHARAN

STRENGTH CHARACTERISTICS OF FIBRE
REINFORCED COMPACTED POND ASH
A THESIS SUBMITTED IN PARTIAL FULFILMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
Master of Technology
in
Civil Engineering
By
ALOK SHARAN
Roll No.-209CE1047
DEPARTMENT OF CIVIL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
ODISHA-769008
MAY 2011
STRENGTH CHARACTERISTICS OF FIBRE
REINFORCED COMPACTED POND ASH
A THESIS SUBMITTED IN PARTIAL FULFILMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
Master of Technology
in
Civil Engineering
By
ALOK SHARAN
Roll No.-209CE1047
Under the guidance of
Dr. S.P. Singh
DEPARTMENT OF CIVIL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
ODISHA-769008
MAY 2011
National Institute of Technology
Rourkela
CERTIFICATE
This is to certify that the thesis entitled “STRENGTH CHARACTERISTICS OF FIBRE
REINFORCED COMPACTED POND ASH” submitted by Mr. ALOK SHARAN in partial
fulfilment of the requirements for the award of Master of Technology Degree in Civil
Engineering with specialization in Geo-Technical Engineering at the National Institute of
Technology, Rourkela (Deemed University) is an authentic work carried out by him under my
supervision and guidance.
To the best of my knowledge, the matter embodied in the thesis has not been submitted to any
other University/ Institute for the award of any degree or diploma.
Date:
Dr. S.P. Singh
Department of Civil Engineering
National Institute of Technology
Rourkela – 769008
ACKNOWLEDGEMENT
The satisfaction and euphoria on 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 out effort with success.
I am grateful to the Dept. of Civil Engineering, NIT ROURKELA, for giving me the
opportunity to execute this project, which is an integral part of the curriculum in M.Tech
programme at the National Institute of Technology, Rourkela.
I would like to take this opportunity to express heartfelt gratitude for my project guide Dr. S.P.
Singh, who provided me with valuable inputs at the critical stages of this project execution. My
special thanks are due to Prof. M. Panda, Head of the Civil Engineering Department, for all the
facilities provided to successfully complete this work. I am also very thankful to all the faculty
members of the department, especially Geo-Technical Engineering specialization for their
constant encouragement during the project.
Submitting this thesis would have been a Herculean job, without the constant help,
encouragement, support and suggestions from my friends and seniors, especially Nemi,
Pragyan, Rabi Narayan Behra and Meena Murmu for their timely help. I will relish your
memories for years to come. I am also thankful to staff members of soil engineering laboratory
especially Mr. Chamuru suniani and Mr. Narayan Mohanty for their assistance and co-operation
during the course of experimentation.
Last but not the least I would like to thank my parents, who taught me the value of hard work by
their own example. I would like to share this bit of happiness with my mother and father. They
rendered me enormous support during the whole tenure of my stay at NIT, Rourkela.
Date:
Alok Sharan
Roll No:-209CE1047
M.Tech (Geo-Technical Engineering)
Department of Civil Engineering
NIT, Rourkela, Odisha
SYNOPSIS
At present about 130 million tonnes of ash is being produced annually from the coal based
thermal power plants in India. The power requirements of the country are rapidly increasing in
pace with in industrial developments. Nearly, 73% of India‟s total installed power generation
capacity is thermal of which coal based generation are nearly 90% (by diesel, wind, gas and
steam adding about 10%). Indian coal gives 35 to 45% ash which is responsible for large
volumes of pond ash. Construction of large ash disposal areas results in resettlement issues and
loss of agricultural production, grazing land and habitat as well as other hand use impacts from
diversion of large areas of land to waste disposal. The current practice in most of the power
plants is to use large ash ponds, and nearly 75,000 acres of land is presently occupied by ash
ponds sometimes in excess of 80,000 acres, which usually involves resettlement issues. Since,
land holdings are typically small in size; a large ash pond development can cause hardships
through loss of land-based subsistence and livelihood for literally thousands of people.
Considering these factors, effective utilization of pond ash in geo-technical
constructions as a replacement to conventional earth materials needs special attention. The
inherent strength of the compacted pond ash mass reduces considerably due to saturation. In this
context to improve and retain the strength of compacted pond ash, cementing agents like cement
or lime may be very much beneficial. The stress-strain behavior of compacted pond ash mass can
be modified by inclusion of fibre reinforcements. Fibre reinforcements also improve the strength
characteristics of the mass. Although, the use of reinforced earth materials has been widely
accepted in many areas like embankments, foundations medium, railroads, retaining walls but
the utilization of pond ash in place of earth material has not drawn much attention of researchers.
The present work aims at evaluating the geo-engineering properties of compacted
pond ash and also the effectiveness of fibre inclusions in the strength characteristics of
compacted pond ash specimens through a series of shear test, unconfined compression test and
CBR test. For this purpose, a polyester fibre (Recron-3s) of 6mm and 12mm in length size is
used with the pond ash, collected from Rourkela Steel Plant (RSP). The fibre content was varied
as 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, and 1.0% of the dry weight of pond ash. The effect of fibre
reinforcement on compacted density has been studies using the light and heavy compaction test.
Compressive strength and shear strength behaviour of compacted samples were studied using
unconfined compressive strength test and direct shear test respectively. The suitability of
compacted pond ash fibre mixes as a road base and sub-base material have been studied by
conducting laboratory CBR tests. The results have been interpreted in terms of stress-strain
behavior, variation of failure stress, variation of failure strain, effect of degree of saturation,
effect of fibre content, strength ratio, and secant modulus and strength parameters and are
presented in this thesis.
Based on the experimental findings the following conclusions are drawn:
 The pond ash consists of grains mostly of fine sand to silt size with uniform gradation of
particles. The specific gravity of particles is lower than that of the conventional earth
materials.
 An increase in compaction energy results in closer packing of particles resulting in an
increase in dry density where as the optimum moisture content decreases.

Dry unit weight of compacted specimens is found to change from 10.90 to 12.70kN/m3 with
change in compaction energy from 357 to 3488kJ/m3, whereas the OMC is found to
decrease from 38.82 to 28.09%.
 Both the unit cohesion and angle of internal friction increase with increase in compaction
energy. A nonlinear relation between these parameters is found to exist with compaction
energy.
 For unreinforced compacted pond ash specimens, the value of unit cohesion increases with
degree of saturation up to the OMC and thereafter the same decreases. The highest value of
unit cohesion occurs at OMC for samples compacted both at standard and modified
densities. However, there is a continuous decrease of angle of internal friction value with
degree of saturation. Initially there is a sharp decrease which gets stabilized at moisture
contents higher than OMC.
 The unit undrained cohesion of reinforced specimens is found to increase with the fibre
content. However, the rate of increase of unit undrained cohesion with fibre content is not
linear. Initially the rate of increase is high thereafter the increase in unit cohesion is not that
prominent.
 For a given compacted density and fibre content, the 12mm size fibre gives higher strength
than 6mm size fibres.
 The highest value of unconfined compressive strength is found to be 12kPa and 29kPa at a
degree of saturation of 13% and 14 % for samples compacted at standard and modified
proctor density. Moisture content either higher or lower than the said value results in
decrease in the compressive strength.

The failure stresses as well as initial stiffness of unreinforced samples, compacted with
greater compaction energies, are higher than the samples compacted with lower compaction
energy. However the failure strains are found to be lower for samples compacted with higher
energies. The failure strains vary from a value of 0.75 to 1.75%, indicating brittle failures in
the specimens.
 An almost linear relationship is found to exist between the compaction energy and
unconfined compressive strength.
 The UCS value of unreinforced specimens is found to change from 1.2 to 17.0kPa with
change in compaction energy from 357 to 3488kJ/m3 indicating that the strength can be
modified suitably by changing the compactive effort. It revealed from the test results that a
linear relationship exists between the initial tangent modulus with unconfined compressive
strength and deformation modulus.
 The trend observed in the CBR value with moisture content is very much similar to that
observe with unconfined compressive strength value of specimens. This shows that for a
given compacted dry density higher unconfined compressive strength as well as CBR value
can be obtained with moulding water content much lower than the OMC value.
 At low strain levels the bearing resistance is found to remain almost constant with fibre
content. However at higher strain level the bearing resistance is found to increases
substantially with increase in fibre content. It is observed that for a given compacted density
an increase in fibre content results in decrease of initial stiffness whereas the failure strain
increases.
 The inclusion of fibre gives ductility to the specimens. The reduction in post peak stress of a
reinforced sample is comparatively lower than the unreinforced sample.
The strength parameters achieved in the present study is comparable to the good
quality, similar graded conventional earth materials. Hence, it can be safely concluded that
reinforced pond ash can replace the natural earth materials in geo-technical constructions.
CONTENTS
CHAPTER
DESCRIPTION
PAGE NO
SYNOPSIS
LIST OF TABLES
LIST OF FIGURES
LIST OF NOTATIONS
CHAPTER-1
I
III
VIII
INTRODUCTION
1.1
INTRODUCTION
1
1.2
HISTORICAL BACKGROUND
3
1.2.1
Early Practices
3
1.2.2
Modern Development
3
1.3
PRINCIPLES OF REINFORCED EARTH
4
1.4
EFFECT OF REINFORCEMENT ON SOIL
5
1.4.1
Force Transfer from Soil to Reinforcement
5
1.4.2
Equivalent Confining Stress Concept
5
1.4.3
Pseudo-Cohesion Concept
8
1.5
REINFORCING MATERIALS
9
1.5.1
General
9
1.5.2
Fibre Reinforced Soil (Ply Soil)
11
1.5.3
Advantages of Fibre-Reinforced Soil
13
1.5.4
Basic Mechanism of RDFS
13
1.5.5
Types of Fibre
14
1.5.6
Direction of Placement
16
1.5.7
Factors Affecting the Strength Characteristics
and other Engineering Properties of RDFS
17
1.6
APPLICATIONS
17
1.7
POND ASH/FLY ASH
18
1.7.1
Factor Affecting Properties of Pond ash
21
1.7.2
Environmental Impact of Pond ash
23
1.7.3
Issues for the Millennium
26
1.7.4
Uses of Pond ash
27
CHAPTER-2
LITERATURE REVIEW
2.1
INTRODUCTION
28
2.2
LITERATURE ON REINFORCED SOIL
28
2.3
LITERATURE ON REINFORCED POND
ASH
2.4
CHAPTER-3
SCOPE OF PRESENT STUDY
EXPERIMENTAL WORK AND
METHODOLOGY
34
38
3.1
INTRODUCTION
39
3.2
MATERIAL USED
39
3.2.1
Pond Ash
39
3.2.1.1
Source of Pond Ash
39
3.2.1.2
Physical Properties of Pond
40
3.2.1.3
Chemical Composition of Pond Ash
40
3.2.2
Geo-Fibre
41
3.2.2.1
Source of Geo-Fibre
41
3.2.2.2
Physical properties of Geo-Fibre
41
3.2.2.3
Role of RECRON-3s
43
3.2.2.4
Primary Applications of RECRON-3
43
3.3
DETERMINATION OF INDEX
PROPERTIES
44
3.3.1
Determination of Specific Gravity
44
3.3.2
Determination of Grain Size Distribution
44
3.4
DETERMINATION OF ENGINEERING
PROPERTIES
44
3.4.1
Moisture Content Dry Density Relationship
44
3.4.2
Determination of Shear Parameters
45
3.4.3
Determination of Unconfined Compressive
Strength
48
3.4.4
CHAPTER-4
Determination of California Bearing Ratio
50
TEST RESULTS AND DISCUSSION
4.1
INTRODUCTION
54
4.2
INDEX PROPERTIES
54
4.2.1
Specific Gravity
54
4.2.2
Grain Size Distribution
54
4.3
ENGINEERING PROPERTIES
55
4.3.1
Compaction Characteristics
55
4.3.2
Shear Parameters
58
4.3.2.1
Effect of compaction energy
58
4.3.2.2
Effect of degree of saturation
60
4.3.2.3
Effect of Fibre content and aspect ratio
63
4.3.3
Unconfined Compressive Strength
69
4.3.3.1
Effect of compaction energy
69
4.3.3.2
Effect of fibre content
73
4.3.3.3
Effect of degree of saturation
78
4.3.4
CBR Value
81
4.3.4.1
Effect of degree of saturation
82
4.3.4.2
Effect of Fibre Content
86
CHAPTER-5
CONCLUSION
92
CHAPTER-6
SCOPE FOR FURTHER STUDIES
95
CHAPTER-7
REFERENCES
96
LIST OF TABLES
SL.NO.
DESCRIPTION
TABLE NO.
PAGE NO.
1
Durability of Reinforcing Materials
Table 1.1
9
2
Degradation Resistances of Various Synthetic Fibres
Table 1.2
10
3
Geosynthetics Applications Summary Table
Table 1.3
17
4
List of Industries Generating Pond ash/Fly ash
Table 1.4
18
5
Chemical Composition of some of the Indian Pond ash
Table 1.5
22
6
Physical Properties of Pond ash
Table 3.1
40
7
Chemical Composition of Pond ash
Table 3.2
41
8
Summaries of Fibre Properties (as supplied by the
Table 3.3
41
Table 3.4
45
Table 3.5
46
Table 3.6
46
Table 3.7
47
Table 3.8
47
Table 3.9
48
manufacturer)
9
Compaction characteristics of unreinforced pond ash
with different compactive effort
10
Shear parameters of unreinforced pond ash (at different
compactive efforts)
11
Shear parameters of unreinforced pond ash (at fixed
standard and modified proctor density varying with
water content)
12
Shear parameters of reinforced pond ash (at standard
and modified proctor density varying with fibre content)
13
Normalized Shear parameters of reinforced pond ash (at
standard and modified proctor density varying with
fibre content)
14
Unconfined compressive strength of compacted
i
unreinforced pond ash (at different compactive efforts)
15
Unconfined compressive strength of unreinforced pond
Table 3.10
49
Table 3.11
49
Table 3.12
50
Table 3.13
51
Table 3.14
52
Table 3.15
52
Table 3.16
53
Table 3.17
53
Table 3.18
53
ash (at fixed standard and modified proctor density
varying with water content)
16
Unconfined compressive strength of reinforced pond
ash (at standard and modified proctor density varying
with fibre content)
17
Normalized Unconfined compressive strength of
reinforced pond ash (at standard and modified proctor
density varying with fibre content)
18
CBR Test result for unreinforced pond ash specimens
with variation moisture content at standard proctor
density of 11.08 kN/m3
19
CBR Test result for unreinforced pond ash specimens
with variation moisture content at modified proctor
density of 12.40 kN/m3
20
Bearing Resistance of reinforced pond ash (at standard
proctor density) for 6mm fibre
21
Bearing Resistance of reinforced pond ash (at modified
proctor density) for 6mm fibre
22
Bearing Resistance of reinforced pond ash (at standard
proctor density) for 12mm fibre
23
Bearing Resistance of reinforced pond ash (at modified
proctor density) for 12mm fibre
ii
LIST OF FIGURES
SL.NO.
DESCRIPTION
FIG.NO. PAGE NO.
1
Stress transfer by soil reinforcement
Fig.1.1
6
2
Confining stress on soil by reinforcement
Fig.1.2
6
3
Equivalent confining stress concept
Fig.1.3
7
4
Scanning electron micrograph (SEM) of pond ash
Fig.3.1
40
5
Views of fibres (Recron-3s)
Fig.3.2
42
6
Scanning electron micrograph (SEM) of fibre (Recron-3s)
Fig.3.3
42
7
Grain size distribution curve of pond ash
Fig.4.1
55
8
Variation of dry density with moisture content at different
Fig.4.2
56
Fig.4.3
57
compaction energy
9
Variation of optimum moisture content with compaction
energy
10
Variation of maximum dry density with compaction energy
Fig.4.4
57
11
Typical Shear Stress versus Normal Stress plots for
Fig.4.5
59
Fig.4.6
59
Fig.4.7
60
Fig.4.8
61
compacted pond ash
12
Variation of unit cohesion with compaction energy for
specimens compacted at OMC & MDD
13
Variation of angle of internal friction with compaction
energy for specimens compacted at OMC &MDD
14
Shear Stress versus Normal Stress plots of specimens with
moisture content at dry density of 11.08kN/m3
iii
15
Shear Stress versus Normal Stress plots of specimens with
Fig.4.9
62
moisture content at dry density of 12.4kN/m3
16
Variation of unit cohesion with degree of saturation
Fig.4.10
63
17
Variation of angle of internal friction with degree of
Fig.4.11
63
Fig.4.12
65
Fig.4.13
66
Fig.4.14
66
Fig.4.15
67
Fig.4.16
67
Fig.4.17
68
Fig.4.18
68
saturation
18
Typical normal stress versus shear stress plots for
reinforced(6mm fibre) pond ash at standard proctor density
19
Typical normal stress versus shear stress plots for
reinforced(6mm fibre) pond ash at modified proctor density
20
Typical normal stress versus shear stress plots for
reinforced(12mm fibre) pond ash at standard proctor density
21
Typical normal stress versus shear stress plots for
reinforced(12mm fibre) pond ash at modified proctor
density
22
Variation of unit cohesion with fibre content for reinforced
(6mm &12mm fibre) pond ash at standard & modified
proctor density
23
Variation of angle of internal friction with Fibre content for
reinforced (6mm &12mm) pond ash at standard & modified
density
24
Fibre content versus normalized cohesion (c‟/c) plots of
reinforced (6mm & 12mm) pond ash at standard and
modified proctor density
iv
25
Fibre content versus normalized coefficient of friction plots
Fig.4.19
69
of reinforced (6mm & 12mm) pond ash at standard and
modified proctor density
26
Stress~strain relationship of compacted pond ash specimens
Fig.4.20
70
27
Variation of unconfined compressive strength with
Fig.4.21
71
Fig.4.22
71
compaction energy.
28
Relationship between energy ratio and strength ratio of
compacted specimens.
29
Variation of tangent modulus with compaction energy.
Fig.4.23
72
30
Initial tangent modulus versus unconfined compressive
Fig.4.24
72
Fig.4.25
73
Fig.4.26
75
Fig.4.27
76
Fig.4.28
76
Fig.4.29
77
Fig.4.30
77
strength.
31
Secant modulus at 50% of failure stress versus Initial
tangent modulus
32
Stress~strain relationship of reinforced (6mm fibre) pond
ash specimens at standard proctor density
33
Stress~strain relationship of reinforced (6mm fibre) pond
ash specimens at modified proctor density
34
Stress~strain relationship of reinforced (12mm fibre) pond
ash specimens at standard proctor density
35
Stress~strain relationship of reinforced (12mm fibre) pond
ash specimens at modified proctor density
36
Variation of unconfined compressive strength with fibre
content for reinforced (6mm &12mm) pond ash at standard
v
& modified proctor density
37
Variation of normalized unconfined compressive strength
Fig.4.31
78
Fig.4.32
79
Fig.4.33
80
with fibre content for reinforced (6mm &12mm) pond ash at
standard & modified proctor density
38
Stress-Strain relationship of compacted pond ash specimens
with moisture content at MDD=11.08 kN/m3.
39
Stress-Strain relationship of compacted pond ash specimens
with moisture content at MDD=12.40 kN/m3.
40
Variation of failure strain with moisture content
Fig.4.34
80
41
Variation of unconfined compressive strength with moisture
Fig.4.35
81
Fig.4.36
83
Fig.4.37
83
content.
42
Load vs Penetration curve for different water content at dry
density of 12.04kN/m3
43
Load vs Penetration curve for different water content at dry
density of 11.08kN/m3.
44
Variation of CBR Value with moisture content
Fig.4.38
84
45
Variation of Normalized CBR with moisture content
Fig.4.39
84
46
Relationship between UCS versus CBR value
Fig.4.40
85
47
Variation of UCS/CBR with moisture content
Fig.4.41
85
48
Typical load versus penetration curves of reinforced (6mm
Fig.4.42
87
Fig.4.43
88
fibre) pond ash specimens at standard proctor density
49
Typical load versus penetration curves of reinforced (6mm
fibre) pond ash specimens at modified proctor density
vi
50
Typical Load versus Penetration curves of reinforced
Fig.4.44
88
Fig.4.45
89
Fig.4.46
89
Fig.4.47
90
Fig.4.48
90
Fig.4.49
91
(12mm fibre) pond ash specimens at standard proctor
density
51
Typical Load versus Penetration curves of reinforced
(12mm fibre) pond ash specimens at modified proctor
density
52
Bearing Resistance versus Fibre Content curves for
reinforced (6mm fibre) pond ash of different strain level at
standard proctor density
53
Bearing Resistance versus Fibre Content curves for
reinforced (6mm fibre) pond ash of different strain level at
modified proctor density
54
Bearing Resistance versus Fibre Content curves for
reinforced (12mm fibre) pond ash of different strain level at
standard proctor density
55
Bearing Resistance versus Fibre Content curves for
reinforced (12mm fibre) pond ash of different strain level at
modified proctor density
vii
LIST OF NOTATIONS
The principal symbols used in this thesis are presented for easy reference. A symbol is used for different
meaning depending on the context and defined in the text as they occur.
NOTATION
DESCRIPTION
E
Compaction Energy, kJ/m3
OMC
Optimum Moisture Content, %
MDD
Maximum Dry Density, kN/m3
cu
Unit Cohesion, kN/m2
Φ
Angle of Internal Friction, degrees
UCS
Unconfined Compressive Strength, kN/m2
FS
Failure Strain, %
SL
Strain Level, %
FC
Fibre Content, %
BR
Bearing Resistance, kN/m2
M.C
Moisture Content, %
CBR
California Bearing Ratio, %
Es50
Secant Modulus, kN/m2
Ei
Initial Tangent Modulus, kN/m2
C‟/C
Normalized Cohesion
Cu
Coefficient of uniformity
Cc
coefficient of curvature
G
Specific Gravity
NUCS
Normalized Unconfined Compressive Strength
viii
CHAPTER -1
INTRODUCTION
INTRODUCTION
1.1 INTRODUCTION
Over the last few years, environmental and economical issues have stimulated interest in the
development of alternative materials and reuse of industrial waste/by-products that can fulfill
specification. A material such as pond ash is a residue collected from ash pond near thermal
power plants. Pond ash is a non-plastic and lightweight material having the specific gravity
relatively lower than that of the similar graded conventional earth material. Pond ash is a finecoarse, glass powder recovered from the gases of burning coal during the production of
electricity. These micron-sized earth elements consist primarily of silica, alumina and iron.
Massive generation of pond ash by thermal power plants has become a major cause of concern
for people living in and around thermal power plants. The current rate of generation of coal ash
in India has reached 130 million tons per annum with about 75,000 acres of precious land under
the cover of abandoned ash ponds. It is estimated that the generation of pond ash from coal fired
generation units in India will reach 170 million tons per annum by the year 2012 whereas, the
current rate of utilization of ash is about 35%. This leads to an ever increasing ponding area for
storing ash and related environmental issues. On the other hand, the construction of highways
and roads in India, which has taken a boom in the recent years, requires a huge amount of natural
soil and aggregates. To meet this demand ruthless exploitation of fertile soil and natural
aggregate is being adopted. This has brought the situation to an alarming state. To address these
problems pond ash has been tried in the low lying areas as structural fills and embankment
construction for highways. However, due to lack of sufficient knowledge and confidence its use
has not taken momentum. The basic and essential parameters of pond ash, to be used either as
structural fill or embankment material.
1
The use of reinforcement in improving the strength parameters of geo-materials
has taken momentum due to the availability of variety of synthetic materials commercially at
cheaper rates. The basic principles involved in earth reinforcement techniques are simple and
have been used by mankind for centuries. One of the essential characteristics of reinforced soil is
that it is made with two types of elements, soil grains and reinforcements. The basic mechanism
of reinforced earth involves the generation of frictional forces between the soil and
reinforcement. By means of friction the soil transfers the forces developed in earth mass to the
reinforcement thus developing tension. The earth develops pseudo cohesion in the direction in
which reinforcement is placed and the cohesion is proportional to tension developed in
reinforcement.
Some research work has been carried out to find the suitability of compacted pond
ash in geotechnical construction like embankments, retaining walls, structural fills, etc However,
these structures are to be protected from getting wet in order to preserve the inherent strength of
the compacted pond ash, which is difficult task in field situations. Keeping this in view the pond
ash sample has been modify the stress-strain behaviour of destabilized material, fibre
reinforcement in the form of recron- 3s were used. The effect of fibre reinforcement on the
stress-strain behaviour, strength parameters of compacted mixes has been evaluated through a
series of unconfined compression tests, direct shear test, CBR test. The test results show that the
inclusions of fibre reinforcement are very efficient in increasing the failure load. The stabilized
pond ash has distinct advantages as there is a little loss of strength due to wetting. Hence, it can
be used in large scale geo-technical construction like base and sub-base courses of roads, airport
pavements, retaining walls, and embankments, structural landfills in conjunction with suitable
reinforcements.
2
1.2 HISTORICAL BACKGROUND
1.2.1Early Practices
Soil specially cohesion less material like gravel, sand and coarse silt cannot take
even low stress in tension and fails instantaneously. The early man has known this phenomenon
from intuition. Men used woven reeds in making sun dried bricks in ancient times even prior to
Christian era. Fibrous materials like vines and papyrus are used in earth structures and mud walls
in Egypt and Babylon. In the construction of the Great Wall of China where are used extensively,
branches of trees were used as reinforcement in the construction of Agar-Quif ziggurat near
Baghdad. Romans who developed a high degree of engineering skills in construction to meet the
civic needs and military requirements built reed reinforced earth leaves along the river Tiber.
Wharf walls in England also were constructed by Romans using wooden scantling as earth
reinforcement. In the last century Col. Palsey introduced reinforced earth for military
construction in British army. The Dutch used reinforced earth by faggoting for sea protective
works.
1.2.2 Modern Development
The modern approach to reinforced earth techniques was first introduced in France and
USA. In 1925, the concept was first introduced by Monster. The structure built was retaining
wall with reinforced earth, wood was used as reinforcement. In the early fifties, the French
constructed retaining walls constructed of granular fill with membrane. This cladding membrane
was anchored with flexible ties. The first major work on reinforced earth was introduced in large
scale from 1964 onwards both in USA and Europe and this was followed by detailed
experimental and theoretical investigation to study the mechanism of the reinforced earth in
France. This programmed was introduced by Henry Vidal and François Schlosser and the
3
scientific approach to the study of reinforced earth structures can be said to have opened up since
then.
However steel was used as reinforcement in the form of stripes which when
exposed to aggressive environment like humidity, access to oxygen and exposure to corrosive
agents rusts rapidly. But with the introduction of such manmade fibres like nylon, propylene and
other forms of organic stable polymers which can withstand ultra-violet light rays and resistant to
acid in industrial applications, the deficiency suffered by steel has greatly been overcome. With
the introduction of such manmade fibres which are found to be superior to natural fibres and
steel it is now feasible to build reinforced earth structure even in soil and environment aggressive
to steel reinforcement.
1.3 PRINCIPLES OF REINFORCED EARTH
Soil mass is generally a discrete system consisting of soil grains and is unable to
withstand tensile stresses and this is particularly true in the case of cohesion less soil like sand.
Such soils cannot be stable on steep slopes and relatively large strains will be caused when
external loads are imposed on them. Reinforced earth is a composite material, a combination of
soil and reinforcement suitably placed to withstand the development of tensile stresses and also
to improve the resistance of soil in the direction of greatest stress. The presence of reinforcement
modifies the stress filed giving a restraint mostly in the form of friction or adhesion so that less
strains are induced and tension is avoided. Inclusions like discrete shot fibres placed random or
in different layers will also impart additional resistance by way of cohesion and friction, but
these are not included in the Vidal‟s concept of reinforced earth.
4
1.4 EFFECT OF REINFORCEMENT ON SOIL
1.4.1Force transfer from soil to reinforcement
Fig. 2.1 shows cohesion less soil mass reinforced by a flat strip. The force at
the two ends of the strip is not same when there is transference of force by friction to the soil
mass (Vidal, 1969). If the average cortical stress in the soil is σv in the region, the difference
between the forces at the ends of a reinforcing element AB of length „dl‟ is given by
dP= σv . 2w. dl. tan Фu……………………………………………………………………………………… (2.1)
where, „w‟ is the width of the reinforcement and is Фu the angle of friction
between the reinforcement and the soil.
Therefore, if we consider a soil mass with spacing at spacing of „Δh‟ and „Δv‟
as shown in the Fig. 2.2 the effect of this reinforcement on the soil mass will be to restraint by
imposing an additional stress of
Δσ3 = Δh (dp/Δv)……………………………………………………………… (2.2)
in the horizontal direction on face AD over that prevailing on face BC.
This restraint on the soil mass increases the resistance of the soil to failure
under applied stresses and the result interpreted in two related ways.
1.4.2 Equivalent confining stress concept
Fig 2.3 (a) shows the comparison of failure stresses on two soils, one
unreinforced and the other reinforced. The increase in the deviator stress is seen to be Δσ3 times
Kp, where Kp is the coefficient of passive earth pressure equal to tan2 (45 + Ф/2) and Δσ3 is the
equivalent confining stress on sand imposed by the reinforcement (Yang, 1972).
5
Fig. 1.1 Stress Transfer by Soil Reinforcement
Fig 1.2 Confining Stress on Soil by Reinforcement
6
Fig 1.3 Equivalent Confining Stress Concept
7
1.4.3 Pseudo – Cohesion Concept
This concept (Schlosser and Long, 1974) proposes that the reinforcement
induces an anisotropic or pseudo-cohesion to the soil which depends on the spacing and strength
of the reinforcement. Fig. 2.3 (b) shows the approach. The increase in deviator stress at failure is
Δσ1 = 2c tan (45 + Ф/2)…………………………………………………….... (2.3)
where, „c‟ is the pseudo-cohesion induced in the soil and Ф is the angle of
friction. Both the equivalent confining stress concept and the pseudo-cohesion concept are linked
to the stress induced in the reinforcement. If αf is the force in the reinforcement per unit width of
the soil mass and Δv is the vertical spacing.
αf /Δv is the equivalent confining pressure Δσ3
and Δσ1 = ( αf /Δv ) tan2 (45 + Ф/2)
or Δσ1 = 2c tan (45 + Ф/2) which yields
c= (αf /2Δv) tan (45 + Ф/2)…………………………………………………………... (2.4)
The value of αf is equal to the tensile strength of the reinforcement, if the
reinforcement fails by breakage or the maximum force transferred by the friction between the
soil and reinforcement pulls off.
In the above concept outlined, it is necessary that the reinforcement layer must
be close enough so that there is effective transfer of stress by friction or adhesion as the case may
be and hence the granular soils of high relative density are particularly suitable for use in
reinforced earth. The concept outlined above can also hold good for cohesive soils to a very
limited extent only since the adhesion of the clay to the reinforcement is small and its effect on
reinforcement is small and its effect on restraint doesn‟t have a multiplying effect as in granular
8
materials. Fig 1.4 shows the increase in strength at failure of an untrained clay sample with
reinforcement.
1.5 REINFORCING MATERIALS
1.5.1 General
A number of materials have been reported to be successfully used as
reinforcements such as steels, geofabrics, geogrids, aluminum, glass fiber, wood, rubber and
concrete. In developed countries polypropylene based synthetic fibers and grids are now
preferred due to their available with desired properties and durability. The durability of
reinforcing materials is shown in Table 1.1. However, they are yet to be used widely in India as
they are more costly. The reinforcement may take the form of strips, grids, sheet materials, rope
and other combinations. The major requirements of the reinforcing materials are strength,
durability, ease of handling, high adhesion or friction with soil and availability at low-cost.
The man made polymers are highly restraint to bacteria, alkalis and acid. Degradation
characteristics of polymers are indicated in Table 1.2. Polyamides have a very good mechanical
characteristic including excellent resistance to abrasion and absolute imperviousness to rotting. It
can withstand high temperature without its performance being affected. However, their
performance deteriorates on wetting.
Table 1.1Durability of Reinforcing Materials
Reinforcing
Material
Aluminium
Copper
Galvanised steel
Stainless Steel
Geotextiles
Geogrid
PH Value
Min
6
5
6
5
-
Max
8
9
9
10
-
Maximum
Chloride ion
content
0.05
0.05
0.05
0.05
-
9
Maximum Total
Sulphate (SO3)
0.5
0.5
0.5
0.5
Not affected
Not affected
Maximum
resistivity
(ohm/cm)
3000
2000
5000
3000
-
Polyesters have very good resistance to abrasion and its behaviour in water is
satisfactory. It has high modulus of elasticity and has only negligible creep. It can also withstand
considerable temperature increase.
Polypropylene is also rot-proof, water and most chemical reagents do not affect
its performance. It has only fair resistance to abrasion and is affected by temperature increase. It
has only a tendency to creep. However, a majority of geo-fabrics is manufactured from
polypropylene.
For use as a reinforcing material, the geo-fabrics should possess a high
modulus elasticity, low elongation and satisfactory puncture strength. For use as an asphalted
overlay material, adsorption qualities may also be essential.
Table 1.2 Degradation Resistances of Various Synthetic Fibres
Resistance to
Types of Synthetics
attack by
Polyester
Polyamide
Polyethylene
Polypropylene PVC
Fungus
Poor
Good
Excellent
Good
Good
Insects
Fair
Fair
Excellent
Fair
Good
Vermin
Fair
Fair
Excellent
Fair
Good
Mineral
Good
Fair
Excellent
Excellent
Good
Alkalies
Fair
Good
Excellent
Excellent
Good
Dry heat
Good
Fair
Fair
Fair
Good
Moist heat
Fair
Good
Fair
Fair
Fair
Oxidizing agent
Good
Fair
Poor
Good
-
Abrasion
Excellent
Excellent
Good
Good
Excellent
Ultraviolet light
Excellent
Good
Fair
Good
Excellent
10
Resistance to ultraviolet radiations and surface conformity should be considered for all jobs.
Soil has used as a construction material from times immortal. Being poor in
mechanical properties, it has been putting, challenge to civil engineering‟s to improve its
properties depending upon the requirement which varies from site to site and economic
constrains. There are many techniques employed to improve the engineering and mechanical
properties of soil can be put into five major categories:
(a) Soil stabilization
(b) Reinforced earth
(c) Soil nailing
(d) Texsol
(e)Fiber reinforced oil or ply soil
1.5.2 Fibre Reinforced Soil (Ply Soil)
Randomly distributed fibres reinforced soil –termed as RDFS is among the latest ground
improvement techniques in which fibres of desired type and quantity are added in soil, mixed
randomly and laid in the position after compaction. Thus, the method of preparation of RDFS is
similar to conventional stabilization techniques. RDFS is different from the other soil –
reinforcing methods in its orientation. In reinforced earth, the reinforcement in the form of strips,
sheets, etc. is laid horizontally at specific intervals, where as in RDFS fibres are mixed randomly
in soil thus making a homogenous mass and maintain the isotropy in strength. Modern
geotechnical engineering has focused on the use of planar reinforcement (e.g. metal strips, sheet
11
of synthetic fabrics). However reinforcement of soil with discrete fibres is still a relatively new
technique in geotechnical project.
Concepts involving the reinforcement of soils using fibres have been
used since ancient times. For example, early civilizations added straws and plant roots to soil
bricks to improve their properties, although the reinforcing mechanism may have not been fully
understood. While building the Great Wall of China, the clay soil was mixed with tamarisk
branches. The ancient method of addition of straw of wheat locally called “Turi” to the clay mud
plaster is still very popular in villages. Improvement of soil by trees roots is similar to the work
fibres. Gray (1947, 1978), Waldron (19770 and Wu et al. (1988) reported that plant roots
increase the shear strength of the soil and, consequently the stability of natural slopes. Synthetic
fibres have been used since the late 1980s, when the initial studies using polymeric fibres were
conducted. Specially, triaxial compression tests, unconfined compression tests, direct shear tests
and CBR tests had been conducted to study the effect of fibre reinforcement on strength
characteristics and other engineering properties of RDFS. During last twenty –five years, much
work has been done on strength deformation behavior of RDFS and it has been established
beyond doubt that addition of fibre in soil improves the overall engineering performance of soil.
Among the notable properties that improve are greater extensibility, small loss of post peak
strength, isotropy in strength and absence of planes of weakness. RDFS has been used in many
civil engineering projects in various countries in the recent past and the further research is in
progress for many hidden aspects of it. RDFS is effective in all types of soil (i.e .sand, silt and
clay)
12
1.5.3 Advantages of Fibre-Reinforced Soil
Randomly distributed fiber reinforced soil (RDFS) offers many advantages as listed below:
 Increased shear strength with maintenance of strength isotropy.
 Beneficial for all type of soils (i.e. sand, silt and clay).

Reduce post peak strength loss.
 Increased ductility.

Increased seismic performance.
 No catastrophic failure.
 Great potential to use natural or waste material such as coir fibers, shredded teire and
recycled waste plastic strips and fibers.

Provide erosion control and facilitate vegetation development.

Reduce shrinkage and swell pressure of expansion soil.

No appreciable change in permeability.
 Unlike lime, cement and other chemical stabilization methods, the construction using fiber –
reinforcement is not significantly affected by weather conditions.

Fiber-reinforcement has been reported to be helpful in eliminating the shallow failure on the
slope face and thus reducing the cost of maintenance.
1.5.4 Basic Mechanism of RDFS
Randomly oriented discrete inclusions incorporated into soil improve its load – deformation
behavior by interacting with the soil particles mechanically through surface friction and also by
interlocking. The function of the bond or interlock is transfer the stress from the soil to the
discrete inclusions by mobilizing the tensile strength of discrete inclusion. Thus, fiberreinforcement works as frictional and tension resistance elements.
13
1.5.5 Types of Fibre
Fibers can be classified in two categories: Synthetic fiber and natural Fiber. Some commonly
used fibers are coconut fiber, Sisal fiber, jute, fiber, Cotton fiber, wool fiber, Asbestos fiber, and
metallic fiber and Glass fiber.
 Synthetic Fibres
The various types of synthetic fiber are polypropylene, nylon, plastic, glass
asbestos etc. These are preferred than the natural fibers because of their higher strength and
resistance. Polypropylene fiber are resistant to acidic, alkaline and chemicals (Setty and Rao,
1987). These fibers are high tensile strength, resistance to sea water and high melting point i.e.
1650C.
Polyimide has inherent defect of getting affected by the ultraviolet rays from
sun but as the fibre are enbeded they are not affected. An experience fibre, no chemical changes
has been detected. Synthetic fibers also show a great biological resistance. Polypropylene fibers
are prone to fire and sun light which practically cannot reach inside the soil.
The important properties of polypropylene are; its versatility, excellent
chemical resistance, low density, high melting point and moderate cost. All these make it an
important fibre in construction applications. So far as fibre structure of polypropylene is
concerned, fibers are composed of crystalline and non- crystalline regions. Fibre spinning and
rawing may cause the orientation of both crystalline and amorphous regions. The degree of
crystallinity of polypropylene fibre is generally between 50-60%, depending on processing
conditions. Crystallization occurs between glass transition temperature and equilibrium melting
temperature point. Polypropylene fibres are being used extensively throughout the USA and
14
Canada in all types of concrete construction, and they have proven to be an effective method of
controlling un-using and troublesome shrinkage cracking in concrete. Polypropylene fibres were
tested in eight different media (distilled water, iron, bacteria culture, seawater and soil) for
seventeen months and found no degradation. Results showed that there was no change in tensile
strength. Plastic fibres show loss in strength with temperature. Nylon is comparable with
polypropylene as for as strength, chemical innerness and durability is concerned. Steel fibres are
prone to rust and acids. Glass fibres although costly but they can bear temperature up to 1500 F.
Asbestos, glass, carbon fibre have been found to be resistant to alkaloids and other chemicals
attack. But long exposure to adverse environment, asbestos fibres has been found to lead to
corrosion damage.
 Natural Fibres
The various types of natural fibre available in India are: coir, sisal, jute, bhabar,
hemp, munja, bamboo and banana. In order to minimize the cost of ply soil, locally available
fibres should be considered in design. But at the same time stability and life of structure should
be given prime importance. Most of these fibres have been tested and found to lose their strength
when subjected to alternate “wetting and drying” environment.
In view of low strength and lack of durability, natural fibres are not in wide use
for reinforcements but are preferred for erosion control due to their environment friendliness and
biodegradability. However, some natural fibres like coir are strong and durable. They can be
made sustainable with proper treatment for reinforcement for reinforcement function in cohesion
less soils and also as filter fabric in cohesive soils.
15
Natural fibres have poor resistance to alkaline environment. Almost all natural
fibres get damaged and lose their strength in 24 hours when given 0.1N solution of sodium
hydroxide (Rehsi , 1988) . The only exception to this is coir. Coir fibres are even resistant to
biodegradation over long period of time. It has been shown that breaking strengths of coir fibre
after 15 years of storage in a hanger comes down from 176 MPa to 160 MPa and elongation from
29% to 21%. It shows that coir becomes slightky brittle with time but best among all natural
fibres.
1.5.6 Direction of Placement
Fibres can be oriented or randomly mixed in soil. In oriented category, the
inclusions are placed within the soil at specific positions and direction where as in random
category, inclusions, are mixed with soil and placed within the probable shear zone. The concept
of randomly reinforced soil is comparatively new in the geotechnical field. French ministry of
public works uses Texsol as RDFS. In the field placing the fibres at some orientation is a tedious
job. In reinforced soil the added material (the Geo synthetic sheet, etc) is layered at specific
direction and position, which may keep the soil weaken in some other direction. Whereas in ply
soil, the isotropy in strength is maintained.
Random reinforcement have been provided to different type of soils in form of
mesh elements, discrete fibres continuous yarn / filament (Texsol) metallic power , waste tire –
chips , waste plastic strips , etc by various investigators.
16
1.5.7 Factors Affecting the Strength Characteristics of Engineering Properties of RDFS
The factors on which the strength characteristics and other engineering properties of RFDS
depend:
(i)
Type of soil it includes soil gradation expressed in terms of mean grain size (D50) and
uniformity coefficient (Cu).
(ii)
Type of Fibre: Monofilament or fibrillated
(iii)
Denier of Fibre: It is the weight (in gm) of 9000 m long fibre.
(iv)
Fibre length
(v)
Aspect ratio: It is defined as the ratio of the length of fibre to its diameter
(vi)
Fibre soil surface friction.
1.6 APPLICATIONS
When designing civil engineering structures, the function to be performed have
to be analyzed first, after those suitable materials and products can be selected. When
geosynthetics are provided, the soil structure requires a strong, relatively stiff and preferably
water permeable material. Table 1.3 gives functional applications of geosynthetics.
Table 1.3 Geosynthetics Applications Summary Table
Application
Primary Function
Products
Sub grade Stabilization
Separation/Reinforcement/Filtration
Geotextiles/Geogrid
Railroad Track Bed
Stabilization
Sedimentation Control Silt
Drainage /Separation Filtration
Geotextiles/Geogrid
Sediment Retention
Geotextile
Fence
Filtration/separation
Asphalt overlay
Stress Reliving layer/ Waterproofing
17
Geogrid/ Geotextiles
Asphalt overlay
Stress Reliving layer/ Waterproofing
Geogrid/ Geotextiles
Soil reinforcement
/Embankments/Steep
slope/Vertical walls
Erosion control filter
Reinforcement
Geotextiles/Geogrid
Filtration Separation
Geogrid/ Geotextiles
Geomembrane protection
Protection/cushion
Geomembrane
Subsurface drainage
Filtration/Fluid transmission
Surfacial erosion control
Turf reinforcement
Prefabricated drainage
composites
Erosion control mats
1.7 POND ASH/FLY ASH
Pond ash is the by-product of thermal power plants, which is considered as a
waste material and its disposal is a major problem from an environmental point of view and also
it requires a lot of disposal areas. Actually, there are three types of ash produced by thermal
power plants, viz. (1) Fly ash, (2) bottom ash, and (3) pond ash. Pond ash is collected by
mechanical or electrostatic precipitators from the flue gases of power plant; whereas, bottom ash
is collected from the bottom of the boilers. Then these two types of ash, mixed together, are
transported in the form of slurry and stored in the lagoons, the deposit is called pond ash. Besides
this steel, copper and aluminium plants also contribute a substantial amount of pond ash. Table
1.4 gives the detail of the industries producing pond ash.
Table 1.4 List of Industries Generating Pond ash/Fly ash
(A) Thermal power plants
Name of the Industry
Name of the State Situated
Name of the Industry
Kothagendem
Andhra Pradesh
Nellore
Ramagundam
Andhra Pradesh
Vijaywada
18
Bongaigaon
Assam
Lakwa
Narup
Chandrapura
Barauni
Jharkhand
Bokaro
Chandradurg
Bihar
Muzzafarpur
Delhi
Rajghat
Gujarat
Gandhinagar
Patratu
Indraprasta
Badarpur
Utraw
Sabarmati
Utkai
Wanakoi
Singrauli
Uttar Pradesh
Mirjapur
Rihand
Panki
Paricha
Anapara
Obra
RPC
Hardoganj
Tanda
Ferojgandhi
Korba
Madhya Pradesh
Satpura
Amarkantak
Vindhyachal
Gurunanak Dev
Ropar
Kota
Raichur
Karnataka
Ennore
Tamilnadu
Tuticorin
Mettur
Neyveli
19
Trombay
Maharastra
Nasik
Ballarshah
Paras
Chola
Bhusawal
Chandanpur
Koradi
Parli
Tata Elec. Co.
Talcher
Orissa
Durgapur
West Bengal
Bundel
Santadir
Lolaghat
Farakka
DPL
C.E.S.C
Titalagarh
New Cossipore
Mulajore
(B) Steel Industry
Name of the Industry
Name of the State Situated
Bhillai Steel
Madhya Pradesh
Durgapur Steel
West Bengal
Rourkela Steel
Odisha
Bokaro Steel
Jharkhand
HSCO
Burnapur,(W.B)
Salem Steel
Tamil Nadu
Vijay Nagar
Karnataka
Visakhapatnam Steel
Andhra Pradesh
TISCO
Jamshedpur,(Jharkhand)
20
(C) Aluminium Industry
Name of the Industry
Name of the State Situated
BALCO
Korba, (M.P)
NALCO
Odisha
(D) Copper Industry
Name of the Industry
Name of the State Situated
Chandmari Copper Project
Rajasthan
Khetri Copper Project
Rajasthan
Dariba Copper Project
Rajasthan
Indian Copper Complex
Bihar
Rakha Copper Project
Bihar
Malanjkhand Copper Project
M.P
1.7.1 Factors affecting properties of pond ash
Meyer (1976) and Despande (1982) represent that the chemical and physical
composition of a pond ash is a function of several variables.
(1) Coal source
(2) Degree of coal pulverization
(3) Deign of boiler unit
(4) Loading and firing condition
(5) Handling and storage methods.
21
Thus, it is not surprising that a high degree of variability can occur in pond ash
not only between power plants but single power plants. A change in any of the above factors can
result in detectable changes in the pond ash produced. The chemical composition of some of the
Indian pond ash is given in Table 1.5.
Table 1.5 Chemical Composition of some of the Indian Pond ash
Thermal
Plant
SiO3
Al2O3
Fe2O3
CaO
MgO
SO3
LOI
TiO2
Ukkai
52.44
28.12
6.18
3.48
5.44
-
3.88
-
Tuticorn
53.44
22.72
4.48
7.25
3.33
1.34
1.5
-
Bokaro
56.50
25.30
4.10
1.30
1.60
-
18-26
0.5
Delhi
60.10
18.60
6.40
6.30
3.60
-
18-26
-
Hardua
60.78
23.63
6.48
15.59
1.54
-
18-26
-
Korba
58.30
24.64
4.40
5.40
3.90
-
18-26
1.0
Obra
56.15
28.87
8.13
2.29
1.45
1.37
18-26
-
Durgapur
50.65
19.65
18.80
2.20
1.49
-
18-26
-
Satpur
59.70
25.69
7.31
2.0
2.89
1.02
18-26
-
Talcher
47-57
18.31
18.69
0.67
0.28
Trace
1.26
-
Rourkela
45-51
20.25
7.95
2.0-3.0
1.0-1.5
-
18-26
-
Nellore
60.18
18.44
16.28
2.08
1.28
0.58
1.05
-
Neyveli
45-59
23.33
0.6-4.0
5-16
1.5-5
2.50
1-2
0.5-1
Panki
53.44
22.72
6.56
3.22
4.48
-
4.21
-
Chandrapur
56.70
23.80
4.0
2.10
1.40
-
-
Kothagudam 66.74
23.20
6.58
2.71
0.77
0.05
7.411.4
0.30
22
-
Bandel
50-95
24.25
9.95
2.59
3.7
2.91
7.1
-
Panipat
60.64
15.70
2.36
0.80
0.25
-
18.86
-
Paras
55.30
27.81
5.09
3.4
3.08
1.20
3.85
-
Kanpur
49.20
22.00
7.50
2.84
0.98
0.24
15.81
-
1.7.2 Environmental Impact of Pond ash
Some of the current methods of ash disposal can have adverse impacts on the
environment, including: land use diversion and resettlement; water resources allocation and
pollution; air pollution; and human health. In particular:
 The construction of large ash disposal areas results in resettlement issues, and loss of
agricultural production, grazing land and habitat, as well as other land use impacts from
diversion of large areas of land to waste disposal. The current practice in some power plants
is to use large ash ponds, sometimes in excess of 7000 acres, which usually involves
resettlement issues. Since land holdings are typically small in size, a large ash pond
development can cause hardships through loss of land-based subsistence and livelihood for
literally thousands of people.
 The design of the ash disposal areas themselves is frequently inefficient in terms of economy
of land areas usage. There is no uniformity in ash pond engineering practice in India. Some
plants are accumulating ash in shallow ponds by diking off natural low lands, resulting in
inefficient usage of land areas for accumulation of high-volume waste. In these instances,
large areas are inundated and taken out of service for other uses; but the depth of inundation
over much of the areas is shallow, and the proportion of land areas usage to disposal storage
volume is high. Some power generation organizations are piling up the ash to elevations of
23
20-30 meters by using the ash itself as pond embankment material, or a combination of
earthwork and ash for elevated storage of ash; this method results in a greater storage
volume over a smaller area, and therefore a more efficient usage of the area devoted to waste
disposal. The ash generated in the power plant is typically mixed with water to form slurry
which is pumped to an ash pond and is allowed to settle. Some ash ponds are being operated
as one unit. This makes management of ash distribution, water coverage, ash slurry water
recycling and minimization of water losses almost impossible.
 The disposal of ash may pollute water resources, including the contamination of
groundwater from leachate and the contamination of surface water from discharge of ash
pond effluent. Ash pond effluent may be used as a source of irrigation water or potable
supply by locals. Leakage in ash slurry pipelines is exploited for irrigation and potable
supply, since local water resources are scarce, and distribution systems almost non-existent.
Direct consumption of ash-pond effluent can result in the uptake of heavy metals and other
toxins. Indirect consumption of ash-pond effluent contaminations can result from the
ingestion of food crops that have been irrigated with ash-slurry effluent; and the
consumption of livelistock that has consumed water or irrigated crops contaminated by
slurry. Often the ash-pond effluent does not meet Indian standards for total suspended solids
(TSS) due to poor management of the ash-pond for settling. The release of ash-contaminated
(high TSS) water, or slurry contaminated with high total dissolved solids, can result in
contamination of the food chain with heavy metals and other toxins, presents as
contaminants in the effluents.
 There may be air pollution from fugitive dust, when ash deposits dry without water or
vegetation cover. Typically, most of the area of large ash ponds or ash dikes are not covered
24
by water or wetted. The ash dries up and is an excellent source for fugitive dust emissions.
In some instances, reclamation of the dried areas has mitigated fugitive dust emissions. Most
areas where the ash ponds are located already have high ambient air concentrations of
respirable particulates. High levels of respirable particulars are associated with upper
increased incidence of respiratory disease. Fugitive emissions from poorly managed ash
disposal areas can contribute to increased local concentrations of respirable particulates, and
adversely impact human health.
 Operation of once through slurry disposal systems puts additional strain on scarce fresh
water resources. The slurry water could be recycled to avoid water resources pollution and
conserve water. Unfortunately, this is not often implemented. Only recently, some State
Pollution Control Boards have become aware of water quality and conservation issues and
are demanding recycling of ash slurry water in the annual Consent Orders issued to the
power plants within their jurisdiction.
 Reclamation of the ash disposal area is often forestalled by engineering and operational
practice, extending the time the land use is devoted to non-productive waste disposal. Some
ash ponds are being operated as one unit. Operation as one large settling pond means that
reclamation will start, if at all, only at the end of the lifetime of the power plant, which is at
least 25-30 years. The eventual reclamation has to be performed over a large area.
Management of a large area associated with resettlement and rehabilitation (R & R) requires
special attention. The use of reclaimed areas for production of food crops and livestock has
the potential to introduce bio-accumulative contaminants into the food chain. Various nonfood production reclamation techniques have been tried with success, including wood and
silkworm production. The choice of reclamation techniques and subsequent use of the
25
reclaimed areas has the potential to offset the hardships of land ousters and project affected
people.
 Earth dam failures present a safety and pollution hazard. Loss of life could occur from
catastrophic failure of the dam. In addition, any release of ash from such a failure would
impact local aquatic resources, thereby potentially contaminating and eliminating habitat.
Poor maintenance of earth dams can be observed, with many earth dams in a state of
progressive failure, and little observation for monitoring of conditions of earth dam
structures.
1.7.3 Issues for the Millennium
It is estimated that by the end of tenth plan period (March 2007) an additional
124,00MW of power generating capacity expansion will be required in India to meet the rising
energy demand. India shall continue to depend on coal as the prime source of energy.
Consequently issues for the solid waste management for coal based thermal power plants shall
continue to be an area of priority since environmental issues shall hold greater importance in the
21st century.
Keeping in view, India‟s development problems like increasing population,
scarce natural resources specially land, increasing urbanization and energy requirements, it is
only but natural that power generation sector can‟t function in isolation. Pond ash is a resource
material which should be utilized. The past 5 years have witnessed a significant growth in the
technological level with respect to pond ash disposal & utilization in the country and in the next
millennium pond ash in itself is going to emerge as a major industry.
26
1.7.4 Use of pond ash
Pond ash/Fly ash can is used for multifarious applications. Some of the application areas are the
following:

In Land fill and dyke rising.

In Structural fill for reclaiming low areas.

Manufacture of Portland cement

Lime – Flyash Soil Stabilizing in Pavement and Sub-base

In Soil Conditioning

Manufacture of Bricks

Part replacement in mortar and concrete.

Stowing materials for mines.
27
CHAPTER 2
LITERATURE REVIEW
LITERATURE REVIEW
2.1 INTRODUCTION
Pond ash is a waste product of coal combination in thermal power plants. It has
posses problem for the safe disposal and causes economic loss to the power plants. Thus, the
utilization of pond ash in large scale geotechnical constructions as a replacement to conventional
earth material needs special attention. The inherent strength of pond ash can be improved by
reinforcing.
Reinforced earth is a composite material, which is a combination of soil and
reinforcement, suitably placed to withstand the developed tensile stresses and also it improves
the resistance of the soil in the direction of the greatest stress. The essential features of reinforced
earth are the friction between the earth and reinforcement, by means of friction the soil transfer
to the reinforcement the forces built in the earth mass. The reinforcement thus develops tension
when the earth mass is subjected to shear stresses along the reinforcement.
2.2 LITERATURE ON REINFORCED SOIL
Andersland and Khattak (1979) have studied on the RDFS
using the soil kaolinite with Φ
=20°, LL=47.8%, PL= 20.3% and G= 2.7 cellulose fiber (fl=1.6mm, dia=0.02mm, fibre content
16 and 40%).
For this test the triaxial test was conducted. The test result indicates that the
addition of fibre @ 16% increases the peak stress by 43% when pure kaolinite was consolidated
at 1.16 times higher confining pressure than the composite. Φr obtained by C- U triaxial test at
fc of 16% is 80.40°.
Gray and Ohashi (1983) have investigated on RFDS, they reinforced the dry sand (Dr= 20%
and 100 %,) with reed, polypropylene and copper fiber. Their direct shear test result shows that
the shear strength soon reaches a limiting level in all type of fiber.
28
McGown, Andrawes and Hytiris (1985) have reinforced the Mid Ross sand (Cu=5, D50=0.5
mm) with polypropylene fiber (with mesh elements of 50mm×50mm, opening size 6.7
mm×7.1mm and fc= 0.09 to 0.24%). The Drained triaxial and model footing tests results shows
the deviator stress developed at all strains , even at very small strains increased with using the
mesh and also peak stresses in the sand – mesh mixture occurred at slightly.
Gray and Al-Refeai (1986) have studied on Muskegon pure sand (D50= 0.41mm,Cu= 1.5,Φ=390
(Dr=86%) and Φ=320(Dr=21%) reinforced with three types of fibre (Reed,d=1.25mm,
Reed,d=1.75mm
and glass fibres,
d=0.30mm,f1= 13,25,38mm
Geolon200, Typar 3601,Typar 3401 and fiber glass 196 ).
geotextiles:Geolon400,
For this work triaxial compression
test were done to compare the stress-strain response of sand reinforced with continuous and they
investigated the amount of reinforcement, confining stress, inclusion modulus and surface
friction. The result
shows at very low strain (<1%) fabric inclusion loss the compressive
stiffness. The strength increase with fibre content up to a fibre content of 2% by weight and
roughly proportional to fibre aspect ratio.
Setty and Rao (1987) have investigated on Lateritic soil with G=16%, S=60% M=21% and
C=1% Φ=390 at optimum moisture content of 16%, LL=33%, PI=7.3% and reinforced with
polypropylene fibre (dia 0.5mm, fibre content of 0, 1, 2, 3, 4, 5). Triaxial test, CBR and tensile
test were done, each at optimum moisture content. The result shows that using of fibres
increases cohesion and slightly decreases Φ, CBR value improved by 2.2 times only up to 2%
fibre content and also improves dry strength. Cohesion improved to 5.7 times at fibre content of
3%but Φ decreases to 0.78times.
29
Lindh and Eriksson (1990) have reinforced the sand (Cu= 3.5 and D50=0.5mm) with
monofilament polypropylene fibre at fibre content of 0.25% and 0.5%. They were conducted a
field experiment by placing a reinforced sand layer on the existing road surface for field
experiment. Their result shows that no rutting is taken place.
Maher and Gray (1990) have reinforced the coarse sand of nine types at Cu=1 to 4, D50=0.09 to
0.65mm
,
10%
moisture
content
with
fl=22mm),glass(dia=0.3mm,ar=60,08,125,fl=45mm),reed
rubber
(dia=1.1mm,ar=20,
fiber(dia=0.3,ar=20,f=18,24,38mm)
Their Drain triaxial tests shows that low modulus fibres(rubber) contribute little to strength
despite higher interface friction. Faliure surface are plain and oriented at (45+Φ/2).An increase in
particle sphericity is higher in critical confining pressure and lower fibre contribution. Higher
aspect ratio resulted lower confining pressure and increasing shear strength.
Fatani et al. (1991) have studied on the silt sand with Cu=5 D50=0.9, c=10kN/m2, Φ=470 and
reinforced with monofilament fiber of 70mm long, oriented (to the shear plane at 450 to 900) and
random, number varies from 5to 32. The Drained direct test was done at modified proctor dry
density γ = 20.8kN/m3 and optimum moisture content 8.9%, orientation of fiber is perpendicular
to shear plane. The test result shows that fiber placed parallel to slip plane of direct shear box
caused reduction in shear strength. In randomly place, only 10-20% fibres cross the shear plane
is actually impart the strength.
Al-Refeai (1991) have reinforced the two type of sand (with Cu= 1.67, D50=0.18, Φ=350 and
Cu=0.94, 50=0.78, Φ=40.5) with polypropylene mesh (dia=0.4, fl=25&50, fc=0.5-2%),
polypropylene pulp and glass fibres (dia=0.1, fl=2-100, fc=0.5-2%). The triaxial test was
conducted at Dr=50% and 60% at 6% moisture content. The result shows that fine sand gives
30
better than medium sand and rounded sand give higher strength than angular sand optimum value
of polypropylene fibre content is 2%, afterwards strength decreases and aspect ratio is 75. Short
fibres require greater confining stress to prevent pullout.
Bauer and Fatani (1991) have studied on silt sand (with Cu=5, D50=0.9,c=10kN/m2, Φ=470 at
optimum moisture content) reinforced with steel fibre (rigid, dia=3mm,fl=40mm,,random) an
copper(flexible , dia= 0.8mm ,fl=70mm,5,6 and 32 fibres aligned) They investigated the direct
shear test and pull out test at modified proctor density test of 2.08t/m3 and moisture content of
8.9%, Φ=370 and δ=23°. The result shows that the residual strength of composite is 200% to
300% higher than unreinforced soil and well graded soil give highest anchorage capacity.
Maher and Ho (1994) reinforced the Kaoloine (with LL=45, PL=15) with monofilament
polypropylene (dia=0.32,fl=2.5 to 20mm, fc=1 to 5%) and glass fibres (dia= 0.05mm,fl=6 to
25mm ,fc=1 to5%). The unconfined compression test, splitting tension and three point bending
were done and for this test the polypropylene fibre is added from 1% to 5% on soil. The addition
of polypropylene fibres improves the unconfined compressive strength linearly (from 1.2 times
to 1.4) Increasing the fibre length from 5mm to 20 mm, decreases qu from 1.4 to1.2 times.
Michalowski and Zaho(1996) have reinforced the dry sand (with Cu=1.52 and D50=0.89) with
polyamide monofilament and steel fibres (dia0.3,0.4mm aspect ratio 85 and 180 , fibre length
and content 25 and 0.5% respectively) . The triaxial result shows that the addition of steel fibres
increases the peak stress by 20% and presence of fibres inhibited the sample dilation and made
sample stiff, before reaching the failure.
Ranjan et al (1996) have studied on the various type of soil like sand , medium sand, fine sand,
silty sand ,silt (with Cu= 2.3 to 2.4, c=1.8 to31 and Φ=32to34 ) reinforced with polypropylene
31
monofilament (dia = 0.3 mm ar=50to 100 fc=0 to 4%) and coir (monofilament dia= 0.2 mm ,ar
=50 to 125, fc= 0to 4%) and bhabar (dia= 0.2 mm , ar= 50to 125 , fc= 0 to 4%). The result of
Triaxial test (CU) on partially saturated sample of RDFS shows greater ductility, no loss of post
peak strength and increase in stiffness. Due to tensile stress in fibres confining pressure is greater
than critical confining pressure, decreases with increase in aspect ratio and soil fibre surface
friction.
Charan (1996) has studied on silt sand to coarse sand (D50= 0.06-0.5mm) reinforced with
polypropylene (dia=0.3 mm, ar=50to 125, fl=15 to 37, fc= 0.5 to 3%) and natural fibres coir and
bhabar (ar = 50 to 100 fl= 15 to 37 mm, fc=0.5 to 3%). In this triaxial and CBR test were done to
check the failure of composite. Triaxial result shows that confining pressure less than critical
confining i.e1.2, strength of composite is un-affected by improving the density of composite. The
CBR value is improved by 2 times at fibre content at 1.5%.
Wasti and Butun (1996) have reinforced the sand soil (with Cu=3.995, Cc=1.132, D60 = 0.819
mm c= 6.98 ,Φ=47.8°) with polypropylene (30×50 mm small, 50×100mm big size and opening
10×10 mm 50mm long fibre by cutting mesh. They were conducted Laboratory model test on a
strip footing 50mm (width) x 250 mm (length) supported by sand and randomly distributed
polypropylene fibre and mesh element. Results indicate that reinforcement of sand caused an
increase in the ultimate bearing capacity values and settlement at ultimate load. The big mesh
size is superior to other and increases in ultimate bearing capacity.
Ranjan et al. (1999) have reinforced the clay (with LL= 58%, PL= 37%) and sand (γ= 18,
Φ=340&cohesion 10.5kPa) with monofilament polypropylene fibre (dia=0.3mm and δ=210). For
the triaxial test moist sample of clay was drilled to and was filled with mixture of sand and fibre.
32
The triaxial result shows peak of normal stress at 10-20% of axial strain in unreinforced soil, but
reinforced soil do not shows any peak. Shear strength increases linearly with increasing the
amount of fibres up to 2% and residual strength is higher than unreinforced soil.
Santoni et al. (2001) have studied on six types of non plastic cohesion less soils reinforced with
monofilament polypropylene fibre ( denier = 4,15,20 fl=13 to 51 mm ,fc =0 to 1% 0). The
unconfined compressive strength of RDFS
was done at base moisture content 2.6% and
saturation 14%. They obtained the optimum fibre content is 0.8% and fibre content <0.6%
caused strain softening , >0.85 causes strain hardening and qu improves slightly by increasing
aspects ratio.
Gosavi et al.(2004) have studied on the black cotton soil ( Ll=38%,PL=14%,c=41kN/m2,Φ= 140
and CBR=4.9%)
reinforced with fibre glass (d= 0.1mm, aspect ratio =250 and 500mm,
fc=1,2,3% ) mixed randomly. They investigated the direct shear test and CBR test and the result
shows OMC and cohesion(c) increase & MDD and angle of internal friction (Φ) decrease upto
2% of fc than trend were reversed on further increase of fibre content. CBR value is decrease
with increase of fc and safe bearing increase by 33.58% and 29.67% due to addition of glass fiber
with aspect ratio 50 and 500 respectively.
Kumar, Wallia and Bajaj (2007) have reinforced the black cotton soil with properties (Gs=
2.72%, LL=68% PL= 49.65% optimum moisture content = 29.4% maximum dry density =1.32
gm/cc) with polyester synthetic. They investigated of unconfined compression of fly ash, lime
and randomly oriented fibres on the geotechnical characteristics of expansive soil. The result
shows that unconfined compressive strength increases with increase in fibre content, which
shows that fibre are more efficient when soil is subjected to tension rather than compression.
33
Chandra et al. (2008) have reinforced the three types of soil clay, silt and silty sand with
polypropylene fibre of 0.3mm diameter. The fibres were cut into pieces of 15, 25, and 30mm in
length and aspect ratio of 50, 80 and 100 respectively and with percentage of0.75, 1.5, 2.25 and 3
by dry weight of soil. The static triaxial test of unreinforced and reinforced soil was conducted.
Their result shows that the uniaxial compressive strength is 3.824, 4.836 and 9.712 MPa
respectively.
2.3 LITERATURE ON REINFORCED POND ASH
Digioa (1972) says that with drainage, the ash can be effectively and economically utilized as a
fill material to construct stable embankment for land reclamation on which structure can be
safely founded.
Leonards (1972) reported that untreated pulverised coal ash with no cementing quantities was
used successfully as a material for structural fill. Although, the ash was inherently variable, it
could be compacted satisfactorily, if the moisture content was maintained below the optimum
obtained from standard laboratory tests and if the percentage of fines (passing the No.200 sieve)
was below 60%.
Kumar et al. (1999) gives the results of laboratory investigations conducted on silty sand and
pond ash specimens reinforced with randomly distributed polyester fibres. The test results reveal
that the inclusion of fibres in soils increases the peak compressive strength, CBR value, peak
friction angle, and ductility of the specimens. It is concluded that the optimum fibre content for
both silty sand and pond ash is approximately 0.3 to 0.4% of the dry unit weight.
Pandey et al. (2002) attempted to devise the ways for the use of this mixed ash for
manufacturing mixed ash clay bricks successfully. The bricks thus made are superior in
34
structural and aesthetic qualities and portents huge saving in the manufacturing costs with better
consumer response.
Bera et al. (2007) presented the study on compaction characteristics of pond ash. Three different
types of pond ash have been used in this study. The effects of different compaction controlling
parameters, viz. compaction energy, moisture content, layer thickness, mold area, tank size, and
specific gravity on dry density of pond ash are highlighted herein. The maximum dry density and
optimum moisture content of pond ash vary within the range of 8.40–12.25 kN/m3 and 29–46%,
respectively. In the present investigation, the degree of saturation at optimum moisture content of
pond ash has been found to vary within the range of 63–89%. An empirical model has been
developed to estimate dry density of pond ash, using multiple regression analyses, in terms of
compaction energy, moisture content, and specific gravity. Linear empirical models have also
been developed to estimate maximum dry density and optimum moisture content in the field at
any compaction energy. These empirical models may be helpful for the practicing engineers in
the field for planning the field compaction control and for preliminary estimation of maximum
dry density and optimum moisture content of pond ash.
Bera et al. (2007) implemented on the effective utilization of pond ash, as foundation medium.
A series of laboratory model tests have been carried out using square, rectangular and strip
footings on pond ash. The effects of dry density, degree of saturation of pond ash, size and shape
of footing on ultimate bearing capacity of shallow foundations are presented in this paper. Local
shear failure of a square footing on pond ash at 37% moisture content (optimum moisture
content) is observed up to the values of dry density 11.20 kN/m3 and general shear failure takes
place at the values of dry density 11.48 kN/m3 and 11.70 kN/m3. Effects of degree of saturation
on ultimate bearing capacity were studied. Experimental results show that degree of saturation
35
significantly affects the ultimate bearing capacity of strip footing. The effect of footing length to
width ratio (L/B), on increase in ultimate bearing capacity of pond ash, is insignificant for L/B ≥
10 in case of rectangular footings. The effects of size of footing on ultimate bearing capacity for
all shapes of footings viz., square, rectangular and strip footings are highlighted.
Chand et al. (2007) presented the effects of lime stabilization on the strength and durability
aspects of a class F pond ash, with a lime constituent as low as 1.12%, are reported. Lime
contents of 10 and 14% were used, and the samples were cured at ambient temperature of around
30°C for curing periods of 28, 45, 90, and 180 days. Samples were subjected to unconfined
compression tests as well as tests that are usually applied to rocks such as point load strength
tests, rebound hammer tests, and slake durability tests. Unconfined compressive strength (UCS)
values of 4.8 and 5.8 MPa and slake durability indices of 98 and 99% were achieved after 180
days of curing for samples stabilized with 10 and 14% lime, respectively. Good correlations, that
are particularly suitable for stabilized materials of low density and low strength, have been
derived for strength parameters obtained from UCS tests, point load strength tests, and Schmidt
rebound hammer tests, and also between UCS and slake durability index.
Bera et al. (2009) have studied the shear strength response of reinforced pond ash, a series of
unconsolidated undrained (UU) triaxial test has been conducted on both unreinforced and
reinforced pond ash. In the present investigation the effects of confining pressure (σ3), number
of geotextile layers (N), and types of geotextiles on shear strength response of pond ash are
studied. The results demonstrate that normal stress at failure (σ1f) increases with increase in
confining pressure. The rate of increase of normal stress at failure (σ1f) is maximum for three
layers of reinforcement, while the corresponding percentage increase in r1f is around (103%),
when the number of geotextile layers increases from two layers to three layers of reinforcement.
36
With increase in confining pressure the increment in normal stress at failure, ∆r increases and
attains a peak value at a certain confining pressure (threshold value) after that ∆r becomes more
or less constant. The threshold value of confining pressure depends on N, dry unit weight (γd) of
pond ash, type of geotextile, and also type of pond ash.
Ghosh et al. (2010) presents the laboratory test results of a Class F pond ash alone and stabilized
with varying percentages of lime (4, 6, and 10%) and PG (0.5, and 1.0), to study the suitability of
stabilized pond ash for road base and sub-base construction. Standard and modified Proctor
compaction tests have been conducted to reveal the compaction characteristics of the stabilized
pond ash. Bearing ratio tests have been conducted on specimens, compacted at maximum dry
density and optimum moisture content obtained from standard Proctor compaction tests, cured
for 7, 28, and 45 days. Both un-soaked and soaked bearing ratio tests have been conducted. This
paper highlights the influence of lime content, PG content, and curing period on the bearing ratio
of stabilized pond ash. The empirical model has been developed to estimate the bearing ratio for
the stabilized mixes through multiple regression analysis. Linear empirical relationship has been
presented herein to estimate soaked bearing ratio from un-soaked bearing ratio of stabilized pond
ash. The experimental results indicate that pond ash-lime-PG mixes have potential for
applications as road base and sub base materials.
Jakka et al. (2010) studied carried on the strength and other geotechnical characteristics of
pond ash samples, collected from inflow and outflow points of two ash ponds in India, are
presented. Strength characteristics were investigated using consolidated drained (CD) and
undrained (CU) triaxial tests with pore water pressure measurements, conducted on loose and
compacted specimens of pond ash samples under different confining pressures. Ash samples
from inflow point exhibited behaviour similar to sandy soils in many respects. They exhibited
37
higher strengths than reference material (Yamuna sand), though their specific gravity and
compacted maximum dry densities are significantly lower than sands. Ash samples from outflow
point exhibited significant differences in their properties and values, compared to samples from
inflow point. Shear strength of the ash samples from outflow point are observed to be low,
particularly in loose state where static liquefaction is observed.
2.4 SCOPE OF PRESENT STUDY
Thus, through appraisal of the literature review it is observed that several attempts have already
been made by researchers to understand the mechanism of randomly oriented discrete inclusions
incorporated into soil improve its load-deformation behavior by interacting with soil particles
mechanically through surface friction and also by interlocking. However, in the present study an
attempt has been made to improve the geo-engineering properties of compacted pond ash by
polyester fibre (recron-3s). Hence, the experimental programme undertaken investigates:

The effect of compaction energy on shear parameters and unconfined compressive
strength of unreinforced pond ash specimens.

The effect of degree of saturation on shear parameters, unconfined compressive strength
and CBR value of unreinforced pond ash specimens.

The effect of fibre content & aspect ratio on shear parameters, unconfined compressive
strength and CBR value of reinforced pond ash specimens.
38
CHAPTER-3
EXPERIMENTAL WORK
AND METHODOLOGY
EXPERIMENTAL WORK AND METHODOLOGY
3.1 INTRODUCTION
Safe and economic disposal of pond ash is the main concern of coal based
thermal power plants. Large scale utilization of pond ash in geotechnical constructions will
reduce the problems faced by the thermal power plants for its disposal. In this connection
assessment of the behaviour of structures constructed using pond ash is required for stability and
safe functioning of structures. Even through adequate substitute for full scale field tests are not
available; tests at laboratory scale have the advantage of allowing a close control of many of the
variable encountered in practice. The trends and behaviour pattern observed in the laboratory
tests can be used in understanding the performance of the structures in the field and may be used
in formulating mathematical relationship to predict the behaviour of field structures. In the
present work the behaviour of randomly reinforced compacted pond ash has been evaluated
through a series unconfined compression test, Shear strength parameters and CBR tests. Details
of material used, sample preparation and testing procedure adopted has been outlined in this
chapter.
3.2 MATERIAL USED
3.2.1 POND ASH
3.2.1.1 Source of Pond ash
Pond ash used in this study was collected from the thermal power plant of CPPNSPCL, Rourkela Steel Plant. The samples were dried at the temperature of 105-110 degrees.
The ash sample was screened through 2mm sieve to separate out the foreign and vegetative
matters. Then the pond ash samples were stored in airtight container for subsequent use.
39
3.2.1.2 Physical Properties of Pond ash
The physical properties of the pond ash sample passing through 2mm sieve were determined and
are presented in Tables 3.1.
Table 3.1 Physical Properties of Pond ash
Physical parameters
Values
Physical parameters
Values
Colour
Silt &clay (%)
Fine sand (%)
Medium sand (%)
Coarse sand (%)
Light grey
26
73.4
5.6
0
Shape
Uniformity coefficient, Cu
Coefficient of curvature, Cc
Specific Gravity, G
Plasticity Index
Rounded/sub-rounded
2.15
1.25
2.37
Non- plastic
Fig.3.1 Scanning Electron Micrograph (SEM) of Pond ash
3.2.1.3 Chemical composition of Pond ash
The chemical compositions of the pond ash sample passing through 2mm sieve were determined
and are presented in Tables 3.2.
40
Table 3.2 Chemical Composition of Pond ash
Constituents
SiO2
%age
57.80
Constituents
P2O5
Al2O3
25.10
SO3
Fe2O3
8.83
K2O
MgO
0.84
CaO
%age
0.19
Constituents
Na2
%age
0.16
TiO2
1.65
0.82
Carbon
4.10
1.14
Volatile Matter
0.14
0.28
3.2.2 GEO-FIBRE
3.2.2.1 Source of Geo-fibre
Geo-fibre used for the test was bought from the market (shop) of 125gm packet
having different sizes 6mm and 12mm. The fiber used for reinforced pond ash specimens was a
polyester fiber (Recron-3s). These fibers were made from polymerization of pure teraphthalic
acid and Mono Ethylene Glycol using a catalyst. These fibers were found to be widely used in
concrete technology. Fig. 3.1 shows a view of fibres used in this study. Scanning Electron
Micrograph (SEM) of fiber is given in Fig.3.2 which has a special triangular cross-section and
equivalent diameter of fiber was about 32 µm– 55 µm. This special triangular cross-section is
good for anchoring and interaction with pond ash.
3.2.2.2 Physical Properties of Geo-fibre
The physical properties of fibers, as supplied by the manufacturer are shown in Table 3.3.
Table 3.3 Summaries of Fibre Properties (as supplied by the manufacturer)
Property
Colour
Cut length
Denier (d)
Tensile Strength (MPa)
Melting Point (°C)
Values
White
6mm,12mm
1.5
600
>250
Property
Specific Gravity
Equivalent diameter (µm)
Water absorption (%)
Acid resistance
Alkali resistance
Values
1.334
32-55
85.22
Excellent
Good
Note: Denier is a unit of measure for the linear mass density of fibres. It is defined as the mass in
grams per 9000 m.
41
Fig.3.2 Views of fibres (Recron-3s)
Fig.3.3 Scanning Electron Micrograph (SEM) of fiber (Recron-3s)
42
3.2.2.3 Role of RECRON-3s
• Controls Cracking:
RECRON 3s prevents the shrinkage cracks developed during curing making the
structure/plaster/component inherently stronger. Further when the loads imposed on concrete
approach that for failure, cracks will propagate, sometimes rapidly. Addition of RECRON 3s in
concrete and plaster prevents/arrests cracking caused by volume change (expansion &
contraction).
• Reduces water permeability:
A cement structure free from such micro cracks prevents water or moisture from entering and
migrating throughout the concrete. This in turn helps prevent the corrosion of steel used for
primary reinforcement in the structure. This in turn improves longevity of the structure.
• Reduces Rebound In Concrete - Brings Direct Saving &Gain:
RECRON 3s fibers reduce rebound "splattering" of concrete and shotcrete. The raw material
wastage reduces & results in direct saving in terms of raw material. More importantly it saves a
great deal of labour employed for the job, which could be completed earlier.
• Increases Flexibility:
The modulus of elasticity of RECRON 3s is high with respect to the modulus of elasticity of the
concrete or mortar binder. The RECRON 3s fibers help increase flexural strength.
• Safe and Easy To Use:
RECRON 3s fibers are environmental friendly and non hazardous. They easily disperse and
separate in the mix.
3.2.2.4 Primary Applications of RECRON-3s:
• Plain concrete & Wall plastering
43
• Footings, foundations, walls and tanks
• Pipes, burial vaults, pre-stressed beams etc.
• For improving the properties of soil by increasing its strength.
• Roads & pavements
• Bridges and dams
3.3 DETERMINATION OF INDEX PROPERTIES
3.3.1 Determination of Specific Gravity
The specific gravity of pond ash was determined according to IS: 2720 (Part-III, section-1) 1980.
The specific gravity of pond ash was found to be 2.37.
3.3.2 Determination of Grain Size Distribution
For determination of grain size distribution, the pond ash was passed through test sieve having an
opening size 75µ. Sieve analysis was conducted for coarser particles as per IS: 2720 part (IV),
1975 and hydrometer analysis was conducted for finer particles as per IS: 2720 part (IV). The
percentage of pond ash passing through 75µ sieve was found to be 33.7%. Hence the particle
size of pond ash ranges from fine sand to silt size. Coefficient of uniformity (C u) and coefficient
of curvature (Cc) for pond ash was found to be 2.15 & 1.25 respectively, indicating uniform
gradation of samples. The grain size distribution curve of pond ash is presented in Fig. 4.1.
3.4 DETERMINATION OF ENGINEERING PROPERTIES
3.4.1 Moisture Content Dry Density Relationship
The moisture content, dry density relationships were found by using compaction tests as per IS:
2720 (Part 7) 1980. For this test, pond ash was mixed with required amount of water and the wet
sample was compacted in proctor mould either in three or five equal layers using standard
proctor rammer of 2.6 kg or modified proctor rammer of 4.5 kg. The moisture content of the
44
compacted mixture was determined as per IS: 2720 (Part 2) 1973. From the dry density and
moisture content relationship, optimum moisture content (OMC) and maximum dry density
(MDD) were determined. Similar compaction tests were conducted with varying compactive
energy and the corresponding OMC and MDD were determined. This was done to study the
effect of compactive energy on OMC and MDD. The compactive energies used in this test
programme were 357, 595, 1493, 2674, 2790 and 3488 kJ/m3 of compacted volume. The test
results are presented in Table 3.4.
Table 3.4 Compaction characteristics of unreinforced pond ash with different compactive
effort
Sl. No.
1
E
(kJ/m3)
357
OMC
(%)
38.82
MDD
(kN/m3)
10.90
2
595
35.92
11.08
3
1493
31.38
11.60
4
2674
28.30
12.40
5
2790
28.72
12.61
6
3488
28.09
12.70
3.4.2 Determination of Shear Parameters
The shear parameters on unreinforced pond ash specimens compacted to their corresponding
MDD at OMC with compactive effort varying as 357, 595, 1493, 2674, 2790 and3488kJ/m3
were determined as per IS: 2720 (Part 13) 1986[13]. Test specimens were prepared
corresponding to their MDD at OMC. These specimens were of size 60mm×60mm×25mm deep
and sheared at a rate of 1.25 mm/minute. The shear strength parameters of the compacted
specimens were determined from normal stress versus shear stress plots and it is given in Table
45
3.5. To study the effect of degree of saturation on the shear parameters, samples were prepared at
a standard and modified dry density but the moisture contents were varied as desired is given in
Table 3.6. Also, to study the effect of fibre content on the shear parameters, compacted
reinforced pond ash samples were prepared at a standard and modified dry density but the fibre
content were varied as 0.2, 0.3, 0.4, 0.5, 0.75, 1.0% are presented in Table 3.7 and similarly, the
normalized shear parameters are tabulated in Table 3.8.
Table 3.5 Shear parameters of unreinforced pond ash (at different compactive efforts)
1
E
(kJ/m3)
357
OMC
(%)
38.82
MDD
(kN/m3)
10.90
cu
(kN/m2)
0.799
Ф
(°)
37.48
2
595
35.92
11.08
1.440
38.30
3
1493
31.38
11.60
2.753
39.20
4
2674
28.30
12.40
6.638
40.55
5
2790
28.72
12.61
7.373
41.46
6
3488
28.09
12.70
8.363
44.47
Sl. No.
Table 3.6 Shear parameters of unreinforced pond ash (at fixed standard and modified
proctor density varying with water content)
Standar Proctor Density (11.08kN/m2)
Sl. No.
Modified Proctor Density (12.40kN/m2)
1
M.C
(%)
43.09
cu
(kN/m2)
4.7
Ф
(°)
31.2
M.C
(%)
33.96
cu
(kN/m2)
5.8
Ф
(°)
31.8
2
39.50
7.4
31.7
31.13
10.0
32
3
35.91,OMC
10.6
31.7
28.03,OMC
11.6
32.8
4
32.32
7.4
32.8
25.47
9.4
34.4
5
30.52
6.3
33.9
24.05
8.0
34.6
46
Table 3.7 Shear parameters of reinforced pond ash (at standard and modified proctor
density varying with fibre content)
Standard Proctor Density
(11.08kN/m2)
6mm fibre
12mm fibre
cu
Ф
cu
Ф
2
2
(kN/m )
(°)
(kN/m )
(°)
1.44
38.3
1.4403
38.3
Modified Proctor Density
(12.40kN/m2)
6mm fibre
12mm fibre
cu
Ф
cu
Ф
2
2
(kN/m )
(°)
(kN/m )
(°)
6.64
40.6
6.64
40.6
Sl.
No.
Fibre
Content
(%)
1
0%
2
0.2%
4.97
39.4
5.23
41.3
8.56
44.2
12.82
49.2
3
0.3%
5.76
40.2
6.21
42.4
9.08
44.6
14.82
50.2
4
0.4%
7.16
40.5
8.14
43.6
11.50
45.3
16.90
51.5
5
0.5%
9.22
41.9
9.64
44.3
12.21
45.5
17.54
52.3
6
0.75%
10.25
41.4
14.21
45.4
15.45
46.2
19.55
53.3
7
1.0%
13.08
42.9
19.89
51
16.85
47.3
20.72
54.2
Table 3.8 Normalized Shear parameters of reinforced pond ash (at standard and modified
proctor density varying with fibre content)
Sl.
No.
Fibre
Content
(%)
1
0%
2
Standard Proctor Density
(11.08kN/m2)
6mm fibre
12mm fibre
cu
Ф
cu
Ф
Modified Proctor Density
(12.40kN/m2)
6mm fibre
12mm fibre
cu
Ф
cu
Ф
1
1
1
1
1
1
1
1
0.2%
3.45
1.02
3.63
1.09
1.28
1.08
1.93
1.20
3
0.3%
4
1.05
4.31
1.10
1.36
1.09
2.23
1.22
4
0.4%
4.97
1.07
5.65
1.15
1.73
1.10
2.54
1.26
5
0.5%
6.40
1.08
6.69
1.16
1.83
1.11
2.64
1.27
6
0.75%
7.12
1.09
9.86
1.19
2.32
1.13
2.94
1.30
7
1.0%
9.08
1.10
13.81
1.34
2.53
1.160
3.12
1.32
47
3.4.3 Determination of Unconfined Compressive Strength
Unconfined compressive strength tests on unreinforced pond ash specimens compacted to their
corresponding MDD at OMC with compactive effort varying as 357, 595, 1493, 2674, 2790
and3488kJ/m3 were performed according to IS: 2720 (Part 10) 1991. For this test cylindrical
specimens were prepared corresponding to their MDD at OMC in the metallic split mould with
dimension 50mm (dia.) × 100mm (high). These specimens were tested in a compression testing
machine with strain rate of 1.25% per minute till failure of the sample. The unconfined
compressive strengths of specimens were determined from stress versus strain curves plots and it
is given in Table 3.9. To study the effect of degree of saturation on the unconfined compressive
strength, samples were prepared at a standard and modified dry density but the moisture contents
were varied as desired is given in Table 3.10. Also, to study the effect of fibre content on the
unconfined compressive strength, compacted reinforced pond ash samples were prepared at a
standard and modified dry density but the fibre content were varied as 0.2, 0.3, 0.4, 0.5, 0.75,
1.0% are presented in Table 3.11 and similarly, the normalized unconfined compressive strength
are tabulated in Table 3.12.
Table 3.9 Unconfined compressive strength of compacted unreinforced pond ash (at
different compactive efforts)
Sl. No.
1
E
(kJ/m3)
357
OMC
(%)
38.82
MDD
(kN/m3)
10.90
UCS
(kN/m2)
1.20
2
595
35.92
11.08
2.80
3
1493
31.38
11.60
6.60
4
2674
28.30
12.40
14.80
5
2790
28.72
12.61
15.90
6
3488
28.09
12.70
17.00
48
Table 3.10 Unconfined compressive strength of unreinforced pond ash (at fixed standard
and modified proctor density varying with water content)
Sl. No.
Standard Proctor Density (11.08kN/m2)
M.C
Failure Strain
UCS
(%)
(%)
(kN/m2)
Modified Proctor Density (12.40kN/m2)
M.C
Failure Strain
UCS
(%)
(%)
(kN/m2)
1
35.92
1.5
2.82
36.79
2
6.17
2
32.33
1.5
3.384
33.96
2
8.414
3
28.73
1.5
4.512
31.13
2
9.536
4
25.14
1.6
6.204
28.3
1.8
14.023
5
21.55
1.6
7.332
25.47
1.85
14.8
6
17.96
1.4
9.024
22.64
1.75
20
7
14.37
1.4
11.845
19.81
1.8
23
8
10.78
1.1
10.253
16.98
1.6
27.062
9
7.19
0.5
6.837
14.15
1.55
28.753
10
-
-
8.49
1.25
23.5
11
-
-
5.66
1
18.133
Table 3.11 Unconfined compressive strength of reinforced pond ash (at standard and
modified proctor density varying with fibre content)
Standard Proctor Density
(11.08kN/m2)
6mm fibre
12mm fibre
UCS
UCS
2
(kN/m )
(kN/m2)
Modified Proctor Density
(12.40kN/m2)
6mm fibre
12mm fibre
UCS
UCS
2
(kN/m )
(kN/m2)
Sl.
No.
Fibre
Content
(%)
1
0%
2.8
2.8
14.55
14.55
2
0.2%
3.2
4.5
15
22
3
0.3%
3.4
5.5
16
23
4
0.4%
3.6
6
17
24
5
0.5%
3.8
6.5
18
26
6
0.75%
4.4
7
19
29
7
1.0%
5.4
7.5
21
35
49
Table 3.12 Normalized Unconfined compressive strength of reinforced pond ash (at
standard and modified proctor density varying with fibre content)
Standard Proctor Density
(11.08kN/m2)
6mm fibre
12mm fibre
NUCS
NUCS
Modified Proctor Density
(12.40kN/m2)
6mm fibre
12mm fibre
NUCS
NUCS
Sl.
No.
Fibre
Content
(%)
1
0%
1
1
1
1
2
0.2%
1.142
1.607
1.030
1.512
3
0.3%
1.214
1.964
1.099
1.580
4
0.4%
1.285
2.142
1.168
1.649
5
0.5%
1.357
2.321
1.237
1.786
6
0.75%
1.571
2.5
1.305
1.993
7
1.0%
1.928
2.678
1.443
2.405
3.4.4 Determination of California Bearing Ratio
Bearing ratio is one of the vital parameters, used in the evaluation of soil sub grades for both
rigid and flexible pavements design. It is also an integral part of several pavement thickness
design methods. To assess the suitability of pond ash a series of bearing ratio tests have been
carried out unreinforced specimens. The bearing ratio tests are conducted in accordance with IS:
2720-16(1961). For this test cylindrical specimens were prepared corresponding to their MDD at
OMC in a rigid metallic cylinder mould with an inside diameter of 150 mm and a height of 175
mm. A mechanical loading machine equipped with a movable base that moves at a uniform rate
of 1.2 mm/min and a calibrated proving ring is used to record the load. For this, Static
compaction is done by keeping the mould assembly in compression machine and compacted the
pond ash by pressing the displacer disc till the level of the disc reaches the top of the mould.
Keep the load for some time, and then release. Remove the displacer disc and then put it under
50
testing machine. To study the effect of degree of saturation on the CBR value, samples were
prepared at a standard and modified dry density but the moisture contents were varied as desired
is given in Table 3.13 and Table 3.14 . Also, to study the effect of fibre content on the bearing
resistance, compacted reinforced pond ash samples were prepared at a standard and modified dry
density of different size of fibre 6mm and 12mm, but the fibre content were varied as 0.2, 0.3,
0.4, 0.5, 0.75, 1.0% are presented in Table 3.15 to Table 3.18.
Table 3.13 CBR Test result for unreinforced pond ash specimens with variation moisture
content at standard proctor density of 11.08 kN/m3
CBR value Normalized
(%)at 5.0 CBR Values
mm
2.5mm
penetration
Penetration
Normalized
CBR Values
5.0mm
(%)
Degree of CBR value
(%) at 2.5
Density Saturation
mm
3
penetration
(kN/m ) (%)
1
43.10
11.08
89.57
0.248
0.232
0.124
0.120
2
39.51
11.08
82.06
0.447
0.497
0.224
0.258
3
35.92,OMC
11.08
74.74
1.988
1.922
1.000
1.000
4
28.73
11.08
59.72
2.784
2.552
1.400
1.327
5
25.14
11.08
52.20
3.480
3.115
1.750
1.620
6
21.55
11.08
44.69
3.629
3.314
1.825
1.724
7
17.96
11.08
37.37
3.977
3.579
2.000
1.862
8
14.37
11.08
29.86
4.773
4.176
2.400
2.172
9
10.78
11.08
22.34
5.916
5.237
2.975
2.724
10
07.19
11.08
14.83
6.563
5.866
3.301
3.052
11
03.59
11.08
7.32
7.259
5.402
3.651
2.810
12
00.00
11.08
0
3.231
2.552
1.625
1.327
Sl.
Moisture
No. Content
Dry
51
Penetration
Table 3.14 CBR Test result for unreinforced pond ash specimens with variation moisture
content at modified proctor density of 12.40 kN/m3
(%)
(kN/m3)
Degree of CBR value
(%) at 2.5
Saturation
mm
(%)
penetration
1
33.96
12.40
88.30
4.226
3.944
0.324
0.331
2
31.13
12.40
80.95
5.718
4.972
0.439
0.417
3
28.30,OMC
12.40
73.61
13.025
11.908
1.000
1.000
4
22.64
12.40
58.72
17.863
15.382
1.371
1.291
5
19.81
12.40
51.38
18.608
15.878
1.428
1.333
6
16.98
12.40
44.04
23.818
18.359
1.828
1.541
7
14.15
12.40
36.70
26.051
20.344
2.000
1.708
8
11.32
12.40
29.36
29.772
24.760
2.285
2.079
9
8.49
12.40
22.02
37.216
29.722
2.857
2.495
10
5.66
12.40
14.68
40.193
33.245
3.085
2.791
11
2.83
12.40
7.34
44.659
34.734
3.428
2.916
12
0
12.40
0
29.772
19.848
2.285
1.666
Sl.
Moisture
No. Content
Dry
Density
CBR value Normalized
(%)at 5.0 CBR Values
mm
2.5mm
penetration
Penetration
Normalized
CBR Values
5.0mm
Penetration
Table 3.15 Bearing Resistance of reinforced pond ash (at standard proctor density) for
6mm fibre
Strain
Levels (%)
Fibre
Content (%)
0
0.2
0.3
0.4
0.5
0.75
1
5
0.434
0.300
0.307
0.334
0.320
0.320
0.374
10
0.514
0.467
0.514
0.614
0.607
0.607
0.701
15
0.594
0.621
0.681
0.794
0.828
0.868
1.002
20
0.641
0.768
0.835
1.062
1.102
1.142
1.315
52
25
0.681
0.908
1.008
1.262
1.336
1.462
1.67
30
0.741
1.035
1.202
1.523
1.636
1.750
1.997
40
0.821
1.342
1.623
1.903
2.124
2.344
2.658
50
0.941
1.623
2.004
2.351
2.651
2.952
3.413
Table 3.16 Bearing Resistance of reinforced pond ash (at modified proctor density) for
6mm fibre
Strain
Levels (%)
Fibre
Content (%)
0
0.2
0.3
0.4
0.5
0.75
1
5
3.175
1.639
1.866
1.639
1.540
1.242
1.391
10
3.999
2.825
3.039
3.172
3.155
3.056
3.379
15
4.060
3.492
3.799
4.158
4.249
4.348
4.746
20
3.636
4.012
4.465
5.065
5.218
5.442
5.964
25
4.023
4.558
5.145
5.905
6.287
6.585
7.330
30
3.284
5.172
5.865
6.731
7.206
7.703
8.573
40
3.090
6.198
7.211
8.277
9.070
9.964
11.232
50
3.333
7.278
8.531
9.930
10.760
12.002
13.344
Table 3.17 Bearing Resistance of reinforced pond ash (at standard proctor density) for
12mm fibre
Strain
Levels (%)
Fibre
Content (%)
0
0.2
0.3
0.4
0.5
0.75
1
5
0.434
0.332
0.332
0.332
0.332
0.372
0.265
10
0.514
0.504
0.544
0.544
0.598
0.598
0.571
15
0.594
0.664
0.757
0.770
0.863
0.890
0.916
20
0.641
0.837
0.943
0.996
1.063
1.196
1.275
25
0.681
0.970
1.129
1.235
1.368
1.541
1.687
30
0.781
1.142
1.328
1.488
1.661
1.926
2.126
40
0.821
1.488
1.740
2.059
2.272
2.697
3.069
50
0.941
1.833
2.126
2.591
2.923
3.521
4.093
Table 3.18 Bearing Resistance of reinforced pond ash (at modified proctor density) for
12mm fibre
Strain
Levels (%)
Fibre
Content (%)
0
0.2
0.3
0.4
0.5
0.75
1
5
3.175
1.478
1.939
1.624
1.308
0.436
0.848
10
3.999
2.351
3.03
2.811
2.496
2.230
2.933
15
4.060
2.836
3.636
3.636
3.393
3.514
4.363
20
3.636
3.466
4.314
4.387
4.242
4.726
5.696
53
25
4.023
3.951
4.993
5.235
5.260
6.181
7.078
30
3.284
4.605
5.623
6.156
6.302
7.272
8.362
40
3.090
5.914
6.859
7.708
8.241
9.526
10.88
50
3.333
7.053
8.168
8.968
9.696
11.15
12.53
CHAPTER-4
TEST RESULTS AND
DISCUSSION
TEST RESULTS AND DISCUSSION
4.1 INTRODUCTION
Pond ash a by-product of the coal based thermal power plants contains grains of fine sand to silt
size. The use of randomly reinforced pond ash in geo-technical constructions requires a proper
understanding of the interaction between the pond ash and reinforced material. The stability of
pond ash reinforced structure depends upon the strength characteristics of the composite
material. A series of conventional laboratory tests such as light and heavy compaction tests,
unconfined compressive strength tests, direct shear tests and CBR tests have been carried out on
compacted pond ash and with different proportion of recron-3s fibre. Test result are presented
and discussed in this chapter.
4.2 INDEX PROPERTIES
4.2.1 Specific Gravity
The specific gravity of pond ash was determined according to IS: 2720 (Part-III, section-1) 1980
and found to be 2.37. The specific gravity of pond ash is found to be lower than that of the
conventional earth material. The specific gravity of pond ash depends on the source of coal,
degree of pulverization and firing temperature. The presence of foreign materials in the fissures
of the coal seams mostly influences the specific gravity of resulting pond ash. Moreover the pond
ash is subjected to mixing with other earth materials during its transportation and depositions,
which influences its specific gravity. Though the chemical composition of pond ash is very much
similar to earth material but as the particles are cenospheres it results in a lower specific gravity.
4.2.2 Grain Size Distribution
The pond ash consists of grains mostly of fine sand to silt size as shown in Fig 4.1. Coefficient of
uniformity and coefficient of curvature are found to be 2.15 & 1.25 respectively, indicating
uniform gradation of samples. The grain size distribution mostly depends on degree of
54
pulverization of coal and firing temperature in boiler units. The presence of foreign materials in
pond ash also influences its grain size distribution. In ash pond the original particles undergoes
flocculation and conglomeration resulting in an increase in particle size.
120
Percentage Finer, (%)
100
80
60
40
20
0
0.01
0.1
Grain Size, (mm)
1
10
Fig.4.1 Grain size distribution curve of pond ash.
4.3 ENGINEERING PROPERTIES
4.3.1 Compaction Characteristics
The compaction characteristics of pond ash with different compaction energies have been studied
by varying the compaction energies as 357, 595, 1493, 2674, 2790 and 3488kJ/m3 of compacted
volume. The OMC and MDD of pond ash samples corresponding to these compactive efforts
have been evaluated and presented in Table 3.4. Relationship between dry density and moisture
content of pond ash at different compaction energies have been shown in Fig 4.2. It is seen that
as the compactive energy increases the MDD increases and the water required to achive this
density is reduced. Plot between OMC and compactive energy (Fig.4.3) shows that initially the
55
OMC decreases rapidly with compactive effort and then the rate of decrease is not that
prominent. A continuous increase in the value of MDD is observed with the compactive energy
(Fig.4.4). The MDD of specimens is found to change from 10.90 to 12.70kN/m3 with change in
compaction energy from 357 to 3488kJ/m3 whereas the OMC is found to decrease from 38.82 to
28.09%. This shows that the compacted density of pond ash responds very poorly to the
compaction energy. This may be attributed to the rounded shape of particles and uniform
gradation of the sample.
Dry Density, (kN/m3)
13
Compaction Energy
357 kJ/m3
595 kJ/m3
1493 kJ/m3
2674 kJ/m3
2790 kJ/m3
3488 kJ/m3
12
11
10
9
15
25
35
45
55
Moisture Content, (%)
Fig.4.2 Variation of dry density with moisture content at different compaction energy.
56
Optimum Moisture Content, (%)
41
39
37
35
33
31
29
27
25
0
1000
2000
3000
4000
Compaction Energy, (kJ/m3)
Fig.4.3 Variation of optimum moisture content with compaction energy.
Maximum Dry Density, (kN/m3)
13
12
11
10
0
500
1000
1500
2000
2500
3000
3500
Compaction Energy, (kJ/m3)
Fig.4.4 Variation of maximum dry density with compaction energy.
57
4000
4.3.2 Shear Parameters
4.3.2.1 Effect of compaction energy
The shear parameters of the compacted pond ash specimens were determined
for specimens compacted to different dry densities and moisture contents. Typical shear stress
and normal stress relationship plots of compacted pond ash are presented in Fig.4.5. It is
observed that the unit cohesion and the angle of internal friction vary from 0.7988 to 8.363kPa
and 37.80 to 44.78 degree with the change in compaction energy from 357 to 3488kJ/m3. The
shear strength parameters of Badarpur and Indraprasta pond ash in loose and dense conditions
were reported by Jakka et al. 2010[15, 16]. The values of angle of internal friction of these pond
ashes varies from 22.3° to 38.6° with zero effective unit cohesion. This shows that the shear
parameters of pond ash is akin to the source as well as degree of compaction moreover the shear
strength properties of pond ash is also a function of source of coal, degree of pulverization
design and firing temperature of boiler units and degree of flocculation of particles in ash pond.
Plot between compaction energy and unit cohesion (Fig.4.6), shows that there exists a nonlinear
relation between them. Initially the rate of increase of unit cohesion with compaction energy is
low followed by a sharp increase. Similar trend is also observed between the angle of internal
friction and compaction energy (Fig.4.7).
58
250
Compaction Energy
357kJ/m3
595kJ/m3
1493kJ/m3
2674kJ/m3
2790kJ/m3
3488kJ/m3
Shear Stress,(kN/m2)
200
150
100
50
0
0
50
100
150
200
250
Normal Stress,(kN/m2)
Fig.4.5 Typical Shear Stress versus Normal Stress plots for compacted pond ash.
Unit Cohesion,(kN/m2)
12
10
8
6
4
2
0
0
500
1000
1500
2000
2500
3000
3500
4000
Compaction Energy,(kJ/m3)
Fig.4.6 Variation of unit cohesion with compaction energy for specimens compacted at OMC &
MDD.
59
Angle of Internal Friction,(Degree)
46
45
44
43
42
41
40
39
38
37
0
500
1000
1500
2000
2500
3000
3500
4000
Compaction Energy,(kJ/m3)
Fig.4.7 Variation of angle of internal friction with compaction energy for specimens compacted
at OMC &MDD
4.3.2.2 Effect of degree of saturation
The effect of degree of saturation on shear parameters were studied by varying
the moulding moisture content from 30.52 to 43.09% for samples compacted at standard Procter
density (11.08kN/m3) and from 24.05 to 33.96% for samples compacted at modified Procter
density (12.40kN/m3). The variations of normal stress and shear stress for the above mentioned
conditions are given in Figs. 4.8 & 4.9 respectively. Plots between unit cohesion and moisture
content (Fig.4.10), show that the unit cohesion increases with degree of saturation up to OMC
and thereafter, the same decreases. The highest value of unit cohesion occurs at OMC for
samples compacted both at standard and modified densities. However, the plot between angle of
internal friction and moisture content (Fig.4.11) show that there is a continuous decrease of angle
of internal friction value with degree of saturation. Initially there is a sharp decrease which gets
stabilized at moisture contents higher than OMC. Pond ash which is non-plastic in nature possess
60
no inter- particular attraction (cohesion), however the compacted samples of specimens posses
negligible amount of cohesion (pseudo-cohesion/apparent cohesion) due to surface tension
effect. The apparent cohesion of compacted specimens of pond ash becomes zero as the sample
becomes completely dry or fully saturated, with the peak apparent cohesion in between. So, in
the presence case the maximum unit cohesion is observed at of OMC of the specimens. The
angle of internal friction of the compacted pond ash is found to be slightly lower than the
conventional earth material of similar gradation. This is obvious because most of the ash
particles are rounded/sub-rounded in shape, devoid of any interlocking properties. There is sharp
decrease in angle of internal friction value of compacted ash sample with degree of saturation.
The added water lubricates the surface of ash particles thus, reducing its angle of internal friction
from 33.8° to 31.5°for standard proctor density and 34.8° to 32° for modified proctor density.
100
Shear Stress, (kN/m2)
90
80
70
60
Moisture Content
50
43.09%
40
39.50%
30
35.91%,OMC
20
32.32%
10
30.52%
0
0
20
40
60
80
100
120
140
Normal Stress, (kN/m2)
Fig.4.8 Shear Stress versus Normal Stress plots of specimens with moisture content at dry
density of 11.08kN/m3.
61
Shear Stress, (kN/m2)
120
100
80
60
Moisture Content
33.96%
40
31.13%
28.03%,OMC
20
25.47%
24.05%
0
0
20
40
60
80
100
120
140
Normal Stress, (kN/m2)
Fig.4.9 Shear Stress versus Normal Stress plots of specimens with moisture content at dry
density of 12.4kN/m3.
Cohesion, (kN/m2)
13
12
Compaction Energy
11
595 kJ/m3
2674 kJ/m3
10
9
8
7
6
5
4
20
25
30
35
40
Moisture Content, (%)
Fig.4.10 Variation of unit cohesion with degree of saturation
62
45
Angle of internal friction(degree)
36
Compaction Energy
595 kJ/m3
2674 kJ/m3
35
34
33
32
31
30
20
25
30
35
40
45
Moisture Content (%)
Fig.4.11 Variation of angle of internal friction with degree of saturation.
4.3.2.3 Effect of Fibre content and aspect ratio
The shear parameters of the pond ash specimens reinforced with two different
sizes of fibres that is 6mm and 12mm length were determined for specimens compacted to
standard and modified proctor density with different percentage of fibre (i.e. 0.2%, 0.3%, 0.4%,
0.5%, 0.75%, and 1.0%). Typical normal stress versus shear stress plots for reinforced (6mm
fibre) pond ash at standard proctor density is presented in Fig.4.12. It is observed that the unit
cohesion and the angle of internal friction vary from 4.97 to 13.08kPa and 39.0 to 42.1 degree
with the change in fibre content from 0.2% to 1.0%. Typical normal stress versus shear stress
plots for reinforced (6mm fibre) pond ash at modified proctor density is presented in Fig.4.13. It
is observed that the unit cohesion and the angle of internal friction vary from 8.56 to 16.85 kPa
and 44.2 to 47.4 degree with the change in fibre content from 0.2% to 1.0%. Similarly, normal
63
stress versus shear stress plots for reinforced (12mm fibre) pond ash at standard proctor density
is presented in Fig.4.14. It is observed that the unit cohesion and the angle of internal friction
vary from 5.24 to 19.89 kPa and 41.5 to 51.0 degree with the change in %age of fibre from 0.2%
to 1.0%. Typical normal stress versus shear stress plots for reinforced (12mm fibre) pond ash at
modified proctor density is presented in Fig.4.15. It is observed that the unit cohesion and the
angle of internal friction vary from 12.82 to 20.72 kPa and 49.3 to 54.3degree with the change in
%age of fibre from 0.2%, to 1.0%. Fig. 4.16 and Fig.4.17 shows the variation of unit cohesion
and angle of internal friction with fibre content for reinforced (6mm &12mm fibre) pond ash
specimens compacted at standard & modified proctor density. The unit undrained cohesion of
reinforced specimens is found to increase with the fibre content. However, the rate of increase of
unit undrained cohesion with fibre content is not linear. Initially the rate of increase is high
thereafter the increase in unit cohesion is not that prominent. Similar trend is also observed
between the angles of internal friction with fibre content. The plots also reveal that the 12mm
size fibre is more effective than 6mm size fibres. The fibres modifies the stress condition in the
specimens and transfer the tensile strain along the failure plane to the surrounding mass by
combined effect of adhesion and friction between the fibre and ash particles. For shorter fibres
(6mm) sufficient anchorage to fibre might not be developed leading to pull-out failure and lesser
mobilization of fibre capacity. In the present case only two fibre lengths have been tried.
However it is expected that for given compacted density an optimum fibre length can be arrive
at, which mobilizes the optimum strength of the fibre.
To have a better idea on the effect of fibre inclusion on the strength parameters
of the compacted pond ash, the shear strength parameters of the specimens i.e. the unit cohesion
and angle of internal friction are expressed in non-dimensional parameters of „normalized
64
cohesion‟ and „normalized coefficient of friction‟. The normalized cohesion is defined as the
ratio of unit cohesion value of fibre reinforced pond ash specimens to the unit cohesion value of
unreinforced pond ash specimens at a given density and moisture content. Similarly, the
normalized coefficient of friction is defined as the ratio of frictional coefficient value of fibre
reinforced pond ash specimens to the frictional coefficient value of unreinforced pond ash
specimens at a given density and moisture content. The variation of normalized cohesion with
fibre content for fibre length of 6mm and 12mm is shown in Fig.4.18, whereas Fig.4.19 gives the
variation of normalized coefficient of friction with fibre content.
200
Fibre Content
Shear Stress(kN/m2)
180
0.00%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
160
140
120
100
80
60
40
20
0
0
20
40
60
80
100
120
140
160
Normal Stress(kN/m2)
Fig.4.12 Typical normal stress versus shear stress plots for reinforced (6mm fibre) pond ash at
standard proctor density
65
160
Fibre Content
Shear Stress(kN/m2)
140
0.00%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
120
100
80
60
40
20
0
0
20
40
60
80
100
120
140
160
Normal Stress(kN/m2)
Fig.4.13 Typical normal stress versus shear stress plots for reinforced (6mm fibre) pond ash at
modified proctor density
300
Shear Stress,(kN/m2)
Fibre Content
250
0.00%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
200
150
100
50
0
0
50
100
150
200
250
Normal Stress,(kN/m2)
Fig.4.14 Typical normal stress versus shear stress plots for reinforced (12mm fibre) pond ash at
standard proctor density
66
350
Fibre Content
Shear Stress,(kN/m2)
300
0.00%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
250
200
150
100
50
0
0
50
100
150
200
250
Normal Stress,(kN/m2)
Fig.4.15 Typical normal stress versus shear stress plots for reinforced (12mm fibre) pond ash at
modified proctor density
Unit Cohesion,(kN/m2)
25
6mm fibre (std.proc.density)
12mm fibre (std.proc.density)
6mm fibre (mod.proc.density)
12mm fibre (mod.proc.density)
20
15
10
5
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
Fibre Content,(%)
Fig.4.16 Variation of unit cohesion with fibre content for reinforced (6mm &12mm fibre) pond
ash at standard & modified proctor density
67
Angle of Internal friction,(kN/m2)
60
6mm fibre (std.proc.density)
12mm fibre (std.proc.density)
6mm fibre (mod.proc.density)
12mm fibre (mod.proc.density)
55
50
45
40
35
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
Fibre Content,(%)
Fig.4.17 Variation of angle of internal friction with Fibre content for reinforced (6mm &12mm)
pond ash at standard & modified density
Normalized Cohesion,C'/C
15
6mm fibre (std.proc.density)
13
12mm fibre(std.proc.density)
6mm fibre(mod.proc.density)
11
12mm fibre (mod. Proc. Density)
9
7
5
3
1
0
0.2
0.4
0.6
0.8
1
1.2
Fibre Content,(%)
Fig.4.18 Fibre content versus normalized cohesion (c‟/c) plots of reinforced (6mm & 12mm)
pond ash at standard and modified proctor density
68
Normalized Coefficient of Friction
1.4
6mm fibre (std.proc.density)
12mm fibre (std.proc.density)
6mm fibre(mod.proc.density)
12mm fibre (mod.proc.density)
1.35
1.3
1.25
1.2
1.15
1.1
1.05
1
0
0.2
0.4
0.6
Fibre Content, (%)
0.8
1
1.2
Fig.4.19 Fibre content versus normalized coefficient of friction plots of reinforced (6mm &
12mm) pond ash at standard and modified proctor density
4.3.3 Unconfined Compressive Strength
4.3.3.1 Effect of compaction energy
Unconfined compressive strength tests were carried out on unreinforced pond
ash specimens compacted to their corresponding MDD at OMC with compactive effort varying
as 357, 595, 1493, 2674, 2790 and3488kJ/m3. Stress-strain relationships of compacted pond ash
were presented in Fig.4.20. Form these plots it is observed that the failure stress as well as initial
stiffness of samples, compacted with greater compaction energy, are higher than the samples
compacted with lower compaction energy. However in general the failure strains are found to be
lower for samples compacted with higher energies. The failure strains vary from a value of 0.75
to 1.75%, indicating brittle failures in the specimens. The increase in unconfined strength and
initial stiffness of specimens with increased compactive effort is attributed to the closer packing
of particles, resulting in the increased interlocking among particles. A closer packing is also
responsible in increasing the cohesion component in the sample. A nonlinear relationship is
found to exist between the unconfined strength and compactive effort (Fig.4.21). Similar
69
relationship is found to exist between strength ratio and compaction energy ratio (Fig.4.22). This
shows that the strength of compacted specimens can be enhanced by increasing the compactive
effort. Deformation modulus is one of the important parameter used for the design of pavement.
It is a key factor for estimating the settlement of foundation resting on pond ash fill or
embankments made of compacted pond ash. The relationship of deformation modulus as a
function of unconfined strength is generally required for design purposes. Figs.4.24 and 4.25
illustrates the relationships between initial tangent modulus (Ei )with unconfined compressive
strength and secant modulus (Es50).It revealed from the test results that a linear relationship exists
between the initial tangent modulus with unconfined compressive strength and deformation
modulus.
Stress,(kN/m2)
18
16
Compaction Energy
14
357kJ/m3
595kJ/m3
1493kJ/m3
2674kJ/m3
2790kJ/m3
3488kJ/m3
12
10
8
6
4
2
0
0
1
2
3
4
5
Strain,(%)
Fig.4.20 Stress~strain relationship of compacted pond ash specimens.
70
6
Unconfined ompressive Strength,(kN/m2)
20
18
16
14
12
10
8
6
4
2
0
0
500
1000
1500
2000
2500
3000
3500
4000
Compaction Energy,(kJ/m3)
Fig.4.21 Variation of unconfined compressive strength with compaction energy.
16
14
Strength Ratio
12
10
8
6
4
2
0
0
1
2
3
4
5
6
7
8
9
10
11
Energy Ratio
Fig.4.22 Relationship between energy ratio and strength ratio of compacted specimens.
71
14000
Stiffness,(kN/m2)
12000
Ei
10000
E50
8000
6000
4000
2000
0
0
500
1000
1500
2000
2500
3000
3500
4000
Compaction Energy, (kJ/m3)
Fig.4.23 Variation of tangent modulus with compaction energy.
14000
Initial Tangent Modulus, Ei
(kN/m2)
12000
10000
8000
6000
4000
2000
0
0
20
40
60
80
100
Unconfined Compressive Strength, (kN/m2)
Fig.4.24 Initial tangent modulus versus unconfined compressive strength.
72
120
Secant Modulus, E50 (kN/m2)
14000
12000
10000
8000
6000
4000
2000
0
0
2000
4000
6000
8000
10000
12000
14000
Initial Tangent Modulus, Ei (kN/m2)
Fig.4.25 Secant modulus at 50% of failure stress versus Initial tangent modulus.
4.3.3.2 Effect of fibre content
The unconfined compressive strength of the pond ash specimens reinforced
with two different sizes of fibres that is 6mm and 12mm length were determined for specimens
compacted to standard and modified proctor density with different percentage of fibre (i.e.
0.1%,0.2%, 0.3%, 0.4%, 0.5%, 0.75%, and 1.0%). Fig.4.26 and Fig.4.27 shows the stress ~ strain
relationship of reinforced (6mm fibre) pond ash specimens at standard and modified proctor
density respectively. Similarly, Fig.4.28 and Fig. 4.29 is presented the stress~strain relationship
of reinforced (12mm fibre) pond ash specimens at standard and modified proctor density
respectively. Variation of unconfined compressive strength with fibre content for reinforced
(6mm &12mm) pond ash at standard & modified proctor density is presented in Fig. 4.30. The
unconfined compressive strength of specimens is found to increase with the fibre content.
However, the rate of increase of strength with fibre content is not linear. Initially the rate of
73
increase is high thereafter the same is not that much prominent. Randomly oriented discrete
inclusions incorporated into granular materials improve its load – deformation behavior by
interacting with the soil particles mechanically through surface friction and also by interlocking.
The bonding and interlocking between the granular particle and reinforcement facilitates the
transfer of the tensile strain developed in the mass to the reinforcement and thus, the tensile
strength of the reinforcement is mobilized and helps in improving the load capacity of the
reinforced mass. The test result shows that the failure stress of reinforced specimen‟s increases
with fibre content both for standard and modified proctor density. The plots also reveal that at
given compacted density and fibre content, the 12mm size fibre gives higher strength than 6mm
size fibres. The fibres modifies the stress condition in the specimens and transfer the shear along
the failure plane to the surrounding mass by combined effect of adhesion and friction between
the fibre and ash particles. For shorter fibres (6mm) sufficient anchorage to fibre might not be
developed leading to pull-out failure and lesser mobilization of fibre capacity. In the present case
only two fibre lengths have been tried. However it is expected that for given compacted density
an optimum fibre length can be arrive at, which mobilizes the optimum strength of the fibre.
To have a better idea on the effect of fibre inclusion on the unconfined
compressive strength of the compacted pond ash, the unconfined compressive strength is
expressed in non-dimensional parameters of normalized unconfined compressive strength. The
normalized unconfined compressive strength is defined as the ratio of unconfined compressive
strength value of fibre reinforced pond ash specimens to that of unreinforced specimens at a
given density and moisture content. The variation of normalized unconfined compressive
strength with fibre content for fibre length of 6mm and 12mm is shown in Fig.4.31. The
normalized unconfined compressive strength is found to be 1.9 and 1.4 for samples reinforced
74
with 1% fibre content and with 6mm fibres to their standard and modified proctor density
respectively. Whereas, these values are 2.7 and 2.4 for samples reinforced with 12mm fibres at
fibre content of 1 %. This clearly indicates that the compressive strength of samples can be
improved with inclusion of discrete fibres and for the present test condition 12mm fibres are
found to more effective in increasing the compressive strength than 6mm fibres.
The stress ~ strain curves as given in Fig.4.26 to Fig.4.29 clearly indicates that
at a given density and increase in fibre content results in decrease of initial stiffness whereas the
failure strain increases. This indicates that inclusion of fibre give ductility to the specimens. It
can further be notice that reduction in post peak strain of a reinforced sample is comparatively
lower than the unreinforced sample. These properties are highly advantages for structures
subjected to dynamic or earthquake loading.
6
Fibre Content
Stress,(kN/m2)
5
0.00%
0.10%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
4
3
2
1
0
0
2
4
6
8
10
12
Strain,(%)
Fig.4.26 Stress~strain relationship of reinforced (6mm fibre) pond ash specimens at standard
proctor density
75
25
Fibre Content
0.00%
0.10%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
Stress,(kN/m2)
20
15
10
5
0
0
1
2
3
4
5
6
7
8
Strain,(%)
Fig.4.27 Stress~strain relationship of reinforced (6mm fibre) pond ash specimens at modified
proctor density
9
Fibre Content
8
0.00%
0.10%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
Stress,(kN/m2)
7
6
5
4
3
2
1
0
0
2
4
6
8
10
12
Strain,(%)
Fig.4.28 Stress~strain relationship of reinforced (12mm fibre) pond ash specimens at standard
proctor density
76
35
Fibre Content
0.00%
0.10%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
Stress,(kN/m2)
30
25
20
15
10
5
0
0
1
2
3
4
5
Strain,(%)
6
7
8
Unconfined Compressive Strength,(kN/m2)
Fig.4.29 Stress~strain relationship of reinforced (12mm fibre) pond ash specimens at modified
proctor density
40
6mm fibre (std.proc.density)
35
12mm fibre(std.proc.density)
6mm fibre (mod.proc.density)
30
12mm fibre (mod.proc.density)
25
20
15
10
5
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
Fibre Content,(%)
Fig.4.30 Variation of unconfined compressive strength with fibre content for reinforced (6mm
&12mm) pond ash at standard & modified proctor density
77
2.8
6mm fibre (std.proc.density)
12mm fibre (std.proc.density)
6mm fibre (mod.proc.density)
12mm fibre (mod.proc density)
2.6
Normalized UCS
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0
0.2
0.4
0.6
0.8
1
1.2
Fibre Content,(%)
Fig.4.31 Variation of normalized unconfined compressive strength with fibre content for
reinforced (6mm &12mm) pond ash at standard & modified proctor density
4.3.3.3 Effect of degree of saturation
The effect of degree of saturation on unconfined compressive strength were
studied by varying the moulding moisture content from 7.19 to 35.92% for samples compacted at
standard Procter density (11.08kN/m3) and from 5.66 to 36.79% for samples compacted at
modified Procter density (12.40kN/m3). The variations of stress and strain for the above
mentioned conditions are given in Figs. 4.32 & 4.33 respectively. Plots between variation of
failure strain with moisture content (Fig.4.34) show that the failure strain increases with degree
of saturation up to OMC and thereafter, the same as in constant at both in standard and modified
proctor density. However, in Fig.4.35 it shows variation of unconfined compressive strength with
moisture content. When the percent of water content reduces from the optimum moisture content
the unconfined compressive strength increases at a sustained degree of saturation of 13% and 14
% and then, decreases in standard and modified proctor density, it is due to the added water
78
lubricates the surface of ash particles. Pond ash which is non-plastic in nature possess no interparticular attraction (cohesion), however the compacted samples of specimens posses negligible
amount of cohesion (pseudo-cohesion/apparent cohesion) due to surface tension effect. The
apparent cohesion of compacted specimens of pond ash becomes zero as the sample becomes
completely dry or fully saturated, with the peak apparent cohesion in between. So, in the
presence case the maximum unconfined compressive strength is observed at of degree of
saturation of 13% and 14 % of the specimens.. This is obvious because most of the ash particles
are rounded/sub-rounded in shape, devoid of any interlocking properties.
14
Variation of M.C.
35.92%,OMC
32.33%
28.73%
25.14%
21.55%
17.96%
14.37%
10.78%
7.19%
12
Stress(kN/m2)
10
8
6
4
2
0
0
1
2
3
4
Strain(%)
5
6
7
8
Fig.4.32 Stress-Strain relationship of compacted pond ash specimens with moisture content at
MDD=11.08 kN/m3.
79
35
Variation of M.C.
36.79%
33.96%
31.13%
28.30%,OMC
25.47%
22.64%
19.81%
16.98%
14.15%
11.32%
8.49%
5.66%
30
Stress(kN/m2)
25
20
15
10
5
0
0
1
2
3
4
5
6
7
8
Strain(%)
Fig.4.33 Stress-Strain relationship of compacted pond ash specimens with moisture content at
MDD=12.40 kN/m3.
2.5
Modified Proctor Density
Failure Strain,(%)
2
Standard Proctor Density
1.5
1
0.5
0
0
5
10
15
20
25
30
Moisture Content,(%)
Fig.4.34 Variation of failure strain with moisture content.
80
35
40
Unconfined Compressive Strength,(kN/m2)
35
Modified Proctor Density
30
Standard Proctor Density
25
20
15
10
5
0
0
5
10
15
20
25
30
35
40
Moisture Content,(%)
Fig.4.35 Variation of unconfined compressive strength with moisture content.
4.3.4 CBR Value
CBR-value is used as an index of soil strength and bearing capacity. This value is broadly used
and applied in design of the base and the sub-base material for pavement. Pond ash is often used
for the construction of these pavement layers and also for embankments. CBR-test was
conducted to characterize the strength and the bearing capacity of the pond ash. In the present
experimental programm two series of test have been conducted in the first series, test have been
conducted unreinforced pond ash specimens compacted to either standard proctor and modified
density with varying degree of saturation. This is done to evaluate the degree of saturation on
CBR value of the specimens. In the second series, tests were conducted on specimens of pond
ash compacted to their MDD at OMC and with fibre content varying as 0%,
,0.2%,0.3%,0.4%,0.5%,0.75%, and 1%. This was done in order to evaluate the inclusion of fibres
on CBR values of reinforced specimens. The test results at presented in the following sections:
81
4.3.4.1 Effect of degree of saturation
The effect of degree of saturation on CBR value were studied by varying the
moulding water content from 3.59 to 43.10% for samples compacted at standard Procter density
(11.08kN/m3) and from 2.83% to 33.96% for samples compacted at modified Procter density
(12.40kN/m3). The load-penetration curves for pond ash were drawn in Fig4.36and Fig4.37
respectively. Plots between variation of CBR Value with moisture content (Fig.4.38) show that
the CBR value increases with decrease in degree of saturation upto a water content of 4% for
samples compacted at standard proctor density and 3% for samples compacted at modified
proctor density, there after the CBR value decreases with moisture content. The highest CBR
value is found to be 7.5% and 45% for samples compacted at standard proctor density and
modified proctor density which corresponds to degree of saturation of 4% and 3% respectively
.The trend observed in Fig. 4.40, the CBR value with moisture content is very much similar to
that observe with unconfined compressive strength value of specimens. This shows that for a
given compacted dry density higher unconfined compressive strength as well as CBR value can
be obtained with moulding water content much lower than the OMC value. This highlights the
influence of degree of saturation on the strength of compacted pond ash specimens.
Fig.4.39 shows that the variation of Normalized CBR with moisture content.
The normalized CBR value is defined as the ratio of CBR value of pond ash specimens at given
moisture content and MDD to that of CBR value of specimens compacted to MDD at OMC. The
trend observed between normalized CBR value and water content very much similar to that of
CBR value and moisture content of pond ash specimens. The maximum normalized CBR value
is found to be for sample compacted to standard and modified proctor density with moulding
82
water content of 4% and 3% respectively. This tells that the CBR value of the compacted pond
ash samples can be retained by protecting it from ingress of water.
9
water content(%)
33.96%
31.13%
28.30%,OMC
25.47%
22.64%
19.81%
16.98%
14.15%
11.32%
8.49%
5.66%
2.83%
0%
8
7
Load,(kN)
6
5
4
3
2
1
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
3
4
5
6
7
8
9
10
11
12
13
Penetration,(mm)
Fig.4.36 Load vs Penetration curve for different water content at dry density of 12.04kN/m3.
2
water content(%)
43.10%
39.51%
35.92%,OMC
32.33%
28.73%
25.14%
21.55%
17.96%
14.37%
10.78%
7.19%
3.59%
0%
1.8
1.6
Load,(kN)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
1
2
Penetration,(mm)
Fig.4.37 Load vs Penetration curve for different water content at dry density of 11.08kN/m3.
83
50
45
Standard Proctor Density
40
Modified Proctor Density
C.B.R (%)
35
30
25
20
15
10
5
0
0
5
10
15
20
25
30
35
40
45
50
Moisture Content,%
Fig. 4.38 Variation of CBR Value with moisture content.
4
Standard Proctor Density
3.5
Normalized CBR
Modified Proctor Density
3
2.5
2
1.5
1
0.5
0
0
5
10
15
20
25
30
35
40
45
Moisture Content,%
Fig. 4.39 Variation of Normalized CBR with moisture content.
84
50
35
Modified Proctor Density
30
Standard Proctor Density
UCS VALUE
25
20
15
10
5
0
0
5
10
15
20
25
30
CBR VALUE
Fig.4.40 Relationship between UCS versus CBR value.
3
Modified Proctor Density
UCS/CBR (kN/m3)
2.5
Standard Proctor Density
2
1.5
1
0.5
0
0
5
10
15
20
25
30
Moisture Content, (%)
Fig 4.41Variation of UCS/CBR with moisture content.
85
35
40
4.3.4.2 Effect of Fibre Content
The bearing resistance of the pond ash specimens reinforced with two
different sizes of fibres that is 6mm and 12mm length was determined for specimens compacted
to standard and modified proctor density with different percentage of fibre (i.e. 0.2%, 0.3%,
0.4%, 0.5%, 0.75%, and 1.0%). These tests were done in a standard CBR mould with a surcharge
load of 2.5kg. Typical load versus penetration curves of reinforced (6mm fibre) pond ash
specimens at standard and modified proctor density are given in Fig.4.42 and Fig.4.43
respectively. Similarly, Fig.4.44 and Fig. 4.45 shows load versus penetration curves of reinforced
(12mm fibre) pond ash specimens at standard and modified proctor density respectively.
Variation of bearing resistance with fibre content for reinforced (6mm and 12mm fibre) pond ash
specimens at different strains level are presented in Fig. 4.46, Fig.4.47 and Fig.4.48, Fig.4.49 for
samples compacted to standard and modified proctor density respectively. The bearing resistance
of specimens is found to increase with the fibre content. However, the rate of increase of strength
with fibre content is not uniform. At low strain levels the bearing resistance is found to remain
almost constant with fibre content. However at higher strain level the bearing resistance is found
to increases substantially with increase in fibre content. This shows that to mobilize the strength
of fibre higher strain is required furthermore; it is observed that for a given compacted density an
increase in fibre content results in decrease of initial stiffness whereas the failure strain increases.
This indicates that inclusion of fibre gives ductility to the specimens. It can further be notice that
reduction in post peak strain of a reinforced sample is comparatively lower than the unreinforced
sample. Randomly oriented discrete inclusions incorporated into granular materials improve its
load – deformation behavior by interacting with the soil particles mechanically through surface
friction and also by interlocking. The bonding and interlocking between the granular particle and
86
reinforcement facilitates the transfer of the tensile strain developed in the mass to the
reinforcement and thus, the tensile strength of the reinforcement is mobilized and helps in
improving the load capacity of the reinforced mass. The test result shows that the failure strain of
reinforced specimen‟s increases with fibre content both for standard and modified proctor
density. The plots also reveal that at given compacted density and fibre content, the 12mm size
fibre gives higher strength than 6mm size fibres. The fibres modifies the stress condition in the
specimens and transfer the shear along the failure plane to the surrounding mass by combined
effect of adhesion and friction between the fibre and ash particles. For shorter fibres (6mm)
sufficient anchorage to fibre might not be developed leading to pull-out failure and lesser
mobilization of fibre capacity. In the present case only two fibre lengths have been tried.
However it is expected that for given compacted density an optimum fibre length can be arrive
at, which mobilizes the optimum strength of the fibre.
4.5
Fibre Content
4
0.00%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
3.5
Load,(kN)
3
2.5
2
1.5
1
0.5
0
0
2.5
5
7.5
10
12.5
15
17.5
20
22.5
25
27.5
30
32.5
Penetration,(mm)
Fig.4.42 Typical load versus penetration curves of reinforced (6mm fibre) pond ash specimens at
standard proctor density
87
16
Fibre Content
14
0.00%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
Load,(kN)
12
10
8
6
4
2
0
0
2.5
5
7.5
10
12.5
15
17.5
20
22.5
25
27.5
30
32.5
Penetration,(mm)
Fig.4.43 Typical load versus penetration curves of reinforced (6mm fibre) pond ash specimens at
modified proctor density
6
Fibre Content
Load,(kN)
5
0.00%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
4
3
2
1
0
0
2.5
5
7.5
10
12.5
15
17.5
20
22.5
25
27.5
30
32.5
Penetration,(mm)
Fig.4.44 Typical Load versus Penetration curves of reinforced (12mm fibre) pond ash specimens
at standard proctor density
88
16
Fibre Content
14
0.00%
0.20%
0.30%
0.40%
0.50%
0.75%
1.00%
Load,(kN)
12
10
8
6
4
2
0
0
2.5
5
7.5
10
12.5
15
17.5
20
22.5
25
27.5
30
32.5
Penetration,(mm)
Fig.4.45 Typical Load versus Penetration curves of reinforced (12mm fibre) pond ash specimens
at modified proctor density
4
Strain Level
Bearing Resistance,(kN/m2)
3.5
5%
10%
15%
20%
25%
30%
40%
50%
3
2.5
2
1.5
1
0.5
0
0
0.2
0.4
0.6
Fibre Content,(%)
0.8
1
1.2
Fig.4.46 Bearing Resistance versus Fibre Content curves for reinforced (6mm fibre) pond ash of
different strain level at standard proctor density
89
16
Bearing Resistance,(kN/m2)
Strain Level
14
5%
10%
15%
20%
25%
30%
40%
50%
12
10
8
6
4
2
0
0
0.2
0.4
0.6
Fibre Content,(%)
0.8
1
1.2
Fig.4.47 Bearing Resistance versus Fibre Content curves for reinforced (6mm fibre) pond ash of
different strain level at modified proctor density.
4.5
Strain Level
Bearing Resistance,(kN/m2)
4
5%
10%
15%
20%
25%
30%
40%
50%
3.5
3
2.5
2
1.5
1
0.5
0
0
0.2
0.4
0.6
Fibre Content,(%)
0.8
1
1.2
Fig.4.48 Bearing Resistance versus Fibre Content curves for reinforced (12mm fibre) pond ash
of different strain level at standard proctor density.
90
14
Bearing Resistance,(kN/m2)
Strain Level
5%
10%
15%
20%
25%
30%
40%
50%
12
10
8
6
4
2
0
0
0.2
0.4
0.6
Fibre Content,(%)
0.8
1
1.2
Fig.4.49 Bearing Resistance versus Fibre Content curves for reinforced (12mm fibre) pond ash
of different strain level at modified proctor density.
91
CHAPTER-5
CONCLUSION
CONCLUSION
 The pond ash consists of grains mostly of fine sand to silt size with uniform gradation of
particles. The specific gravity of particles is lower than that of the conventional earth
materials.
 An increase in compaction energy results in closer packing of particles resulting in an
increase in dry density where as the optimum moisture content decreases.

Dry unit weight of compacted specimens is found to change from 10.90 to 12.70kN/m3 with
change in compaction energy from 357 to 3488kJ/m3, whereas the OMC is found to
decrease from 38.82 to 28.09%. This shows that pond ash sample responds very poorly to
the compaction energy.
 Both the unit cohesion and angle of internal friction increase with increase in compaction
energy. A nonlinear relation between these parameters is found to exist.
 The value of unit cohesion increases with degree of saturation up to the OMC and thereafter
the same decreases. The highest value of unit cohesion occurs at OMC for samples
compacted both at standard and modified densities. However, there is a continuous decrease
of angle of internal friction value with degree of saturation. Initially there is a sharp decrease
which gets stabilized at moisture contents higher than OMC.
 The unit undrained cohesion of reinforced specimens is found to increase with the fibre
content. However, the rate of increase of unit undrained cohesion with fibre content is not
linear. Initially the rate of increase is high thereafter the increase in unit cohesion is not that
prominent.
 The plots also reveal that at given compacted density and fibre content, the 12mm size fibre
gives higher strength than 6mm size fibres. The fibres modifies the stress condition in the
92
specimens and transfer the shear along the failure plane to the surrounding mass by
combined effect of adhesion and friction between the fibre and ash particles.
 When the percent of water content reduces from the optimum moisture content the
unconfined compressive strength increases at a sustained degree of saturation of 13% and 14
% and then, decreases in standard and modified proctor density, it is due to the added water
lubricates the surface of ash particles.
 The failure stresses as well as initial stiffness of samples, compacted with greater
compaction energies, are higher than the samples compacted with lower compaction energy.
However the failure strains are found to be lower for samples compacted with higher
energies. The failure strains vary from a value of 0.75 to 1.75%, indicating brittle failures in
the specimens.
 A linear relationship is found to exist between the compaction energy and unconfined
compressive strength.
 The UCS value is found to change from 1.2 to 17.0kN/m2 with change in compaction energy
from 357 to 3488kJ/m3 indicating that the strength can be modified suitably by changing the
compactive effort. It revealed from the test results that a linear relationship exists between
the initial tangent modulus with unconfined compressive strength and deformation modulus.
 The trend observed in the CBR value with moisture content is very much similar to that
observe with unconfined compressive strength value of specimens. This shows that for a
given compacted dry density higher unconfined compressive strength as well as CBR value
can be obtained with moulding water content much lower than the OMC value. This
highlights the influence of degree of saturation on the strength of compacted pond ash
specimens.
93
 The bearing resistance of specimens is found to increase with the fibre content. However,
the rate of increase of strength with fibre content is not uniform. At low strain levels the
bearing resistance is found to remain almost constant with fibre content.
 However at higher strain level the bearing resistance is found to increases substantially with
increase in fibre content. This shows that to mobilize the strength of fibre higher strain is
required furthermore; it is observed that for a given compacted density an increase in fibre
content results in decrease of initial stiffness whereas the failure strain increases.
 This indicates that inclusion of fibre gives ductility to the specimens. It can further be notice
that reduction in post peak strain of a reinforced sample is comparatively lower than the
unreinforced sample.
Hence, the strength parameters achieved in the present study is
comparable to the good quality, similar graded conventional earth materials. Hence, it can be
safely concluded that pond ash can replace the natural earth materials in geo-technical
constructions.
94
CHAPTER-6
SCOPE FOR FURTHER
STUDIES
SCOPE FOR FURTHER STUDIES
For effective functioning of structures made up of reinforced pond ash, some more aspects have
to be investigated.
 Effect of aspect ratio that is different fibre length on strength parameters and to arrive at
an optimum value.
 Compressibility and Consolidation characteristics of compacted pond ash.
 Bearing capacity of surface and embedded foundations.
 Effect of other natural and synthetic fibres on geo-engineering properties.
 Liquefaction succesbility of fibre reinforced pond ash.
 The decay of organic fibres, creep effect in fibres to be studied.
 The environment aspects arising out of the leachate from the compacted pond ash.
95
CHAPTER-7
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