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STRENGTH OF SOFT CLAY REINFORCED WITH GROUP CRUSHED
POLYPROPYLENE (PP) COLUMNS
NURAINI BINTI YUSUF
Thesis submitted in fulfilment of the requirements for the award of the degree of Bachelor of
Civil Engineering
Faculty of Civil Engineering
UNIVERSITY MALAYSIA PAHANG
JUNE 2015
vi
ABSTRACT
The use of granular columns as soil reinforcement technique has proved useful in
problems of foundation stability and settlement, as well as improving soft clay for
foundation construction. The purpose of this study is to investigate the enhancement of
shear strength of soft kaolin clay when it is reinforced with group crushed polypropylene
(PP) columns. Since PP is a waste material, the cost of soil improvement can be reduced
which currently was disposed totally in large quantity into landfill. In order to proceed the
study, physical and mechanical properties of materials used that are kaolin (soil sample)
and PP (reinforcing columns) must be identify first. Then, consolidated kaolin as soft clay
was reinforced with group crushed PP columns, and subsequently tested under Unconfined
Compression Test (UCT). A total of 7 batches of kaolin sample including control sample
had been tested to identify the shear strength. Each batches involved of four samples to find
the average value of maximum stress. The variables used for the columns installation were
the column height that are 60 mm, 80 mm and 100 mm, where the column penetrating ratio
are 0.6, 0.8 and 1.0 respectively. In addition, different values of columns diameter had been
used that are 6 mm and 10 mm for every different height of columns. A total of 28
unconfined compression tests had been conducted on kaolin samples. The kaolin samples
had the dimensions of 50 mm in diameter and 100 mm in height. For the group PP
reinforcement, shear strength increased about 2.13%, 13.51% and 12.84% for 1.44% area
replacement ratio and 6.85%, 14.26% and 13.79% for 4% area replacement ratio at sample
penetration ratio 0.6, 0.8, 1.0 respectively. In the other hand, the relationship of the
increment of shear strength with the various column penetration ratio show different
pattern. The shear strength of both area replacement ratio increases constantly as the
column penetrating ratio increased, but after it reach 80mm height of column, the shear
strength decrease slightly and this support the ‘critical column length’ idea. It can be
concluded that the shear strength parameters were affected by the diameter and the height
of the columns and the presence of PP column greatly improve the shear strength.
vii
ABSTRAK
Penggunaan tiang granular sebagai teknik pengukuhan tanah telah terbukti
berguna dalam masalah kestabilan asas dan mendapan, serta memperbaiki tanah liat lembut
untuk pembinaan asas. Tujuan kajian ini adalah untuk menyiasat peningkatan kekuatan
ricih tanah liat kaolin lembut apabila ia diperkuatkan dengan tiang berkumpulan
polipropilena (PP) hancur. Memandangkan PP adalah bahan buangan, kos pembaikan tanah
boleh dikurangkan yang kini telah dilupuskan sama sekali dalam kuantiti yang besar ke
tapak pelupusan. Untuk meneruskan kajian ini, sifat-sifat fizikal dan mekanikal bahan-
bahan yang digunakan iaitu kaolin (sampel tanah) dan PP (tiang pengukuhan) mesti dikenal
pasti terlebih dahulu. Kemudian, kaolin yang disatukan sebagai tanah liat lembut
diperkukuh dengan tiang berkumpulan PP hancur, dan kemudiannya diuji di bawah Ujian
Mampatan Tak Terkurung (UCT). Sebanyak 7 kumpulan sampel kaolin termasuk sampel
kawalan telah diuji untuk mengenal pasti kekuatan ricih. Setiap kumpulan mempunyai
empat sampel untuk mencari nilai purata tekanan maksimum. Pemboleh ubah yang
digunakan untuk pemasangan tiang tersebut ialah ketinggian tiang iaitu 60 mm, 80 mm dan
100 mm, di mana nisbah ruang menembusi adalah 0.6, 0.8 dan 1.0. Di samping itu, nilai-
nilai garis pusat tiang yang berbeza telah digunakan iaitu 6 mm dan 10 mm untuk setiap
ketinggian tiang yang berbeza. Sebanyak 28 ujian mampatan tak terkurung telah dijalankan
ke atas sampel kaolin. Sampel kaolin mempunyai dimensi garis pusat 50 mm dan
ketinggian 100 mm. Bagi kumpulan PP tetulang, kekuatan ricih meningkat kira-kira 2.13%,
13.51% dan 12.84% untuk nisbah penggantian kawasan 1.44% dan 6.85%, 14.26% dan
13.79% bagi nisbah penggantian kawasan 4% pada nisbah penembusan sampel 0.6, 0.8,
1.0. Di sisi lain, hubungan antara kenaikan kekuatan ricih dengan pelbagai nisbah
penembusan ruangan mempunyai corak yang berbeza. Kekuatan ricih kedua-dua nisbah
penggantian kawasan sentiasa meningkat apabila nisbah ruang menembusi meningkat,
tetapi selepas ia mencapai ketinggian tiang 80mm, kekuatan ricih menurun sedikit dan ia
disokong oleh idea 'panjang tiang kritikal'. Dapat disimpulkan bahawa parameter kekuatan
ricih terjejas oleh garis pusat dan ketinggian tiang dan kehadiran tiang PP banyak
meningkatkan kekuatan ricih.
viii
TABLE OF CONTENTS
Page
SUPERVISOR’S DECLARATION ii
STUDENT’S DECLARATION iii
DEDICATION iv
ACKNOWLEDGEMENTS v
ABSTRACT vi
ABSTRAK vii
TABLE OF CONTENTS viii
LIST OF TABLES xii
LIST OF FIGURES xiv
LIST OF APPENDICES xviii
LIST OF SYMBOLS xix
LIST OF ABBREVIATIONS xxi
CHAPTER 1 INTRODUCTION
1.1 Background of Research 1
1.2 Problem Statement 5
1.3 Objectives 6
1.4 Scope of Study 6
1.5 Research Significance 8
CHAPTER 2 LITERATURE REVIEW
2.1 Soft Clay 10
2.1.1 Compressibility and Consolidation 12
2.1.2 Shear Strength 14
2.2 Polypropylene (PP) 16
ix
2.2.1 Particle Size 17
2.2.2 Specific Gravity 22
2.2.2 Compaction 23
2.2.4 Shear Strength and Tensile Strength 27
2.2.5 Permeability 30
2.2.6 Compressibility 31
2.3 Vertical Granular Column 33
2.3.1 Shear Strength 34
2.3.2 Consolidation Around Vertical Granular Column 37
2.3.3 Stress Strain Behavior 39
CHAPTER 3 METHODOLOGY
3.1 Introduction 43
3.2 Laboratory Works 45
3.3 Laboratory Tests For Determination of Physical Properties 46
3.3.1 Atterberg Limit Test 46
3.3.2 Specific Gravity Test 48
3.3.3 Sieve Analysis Test 49
3.3.4 Hydrometer Test 50
3.3.5 Relative Density Test 51
3.4 Laboratory Tests for Determination of mechanical Properties 52
3.4.1 Standard Compaction Test 53
3.4.2 Falling Head Permeability Test 54
3.5 Reinforcing Soft Kaolin Clay with Group Crushed PP Columns 56
3.5.1 Samples Preparation 56
3.5.2 Installation of PP Columns 58
3.5.3 Unconfined Compression Test (UCT) 62
x
CHAPTER 4 RESULTS AND DISCUSSIONS
4.1 Background 64
4.2 Physical Properties 65
4.2.1 Atterberg Limit Test 66
4.2.2 Specific Gravity Test 68
4.2.3 Particle Size Distribution 69
4.2.4 Relative Density Test 71
4.3 Mechanical Properties 72
4.3.1 Standard Compaction Test 72
4.3.2 Falling Head Permeability Test 74
4.4 Reinforcing Soft Kaolin Clay With Group Crushed PP Columns 75
4.4.1 Effect of PP Columns on shear Strength 75
4.4.2 The Effect of Area Replacement Ratio 85
4.4.3 The Effect of Column Penetration Ratio 88
CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusion 91
5.2 Recommendation 93
REFERENCES 94
APPENDICES 98
A Properties of Polypropylene 98
B Atterberg Limit Test 99
C Specific Gravity Test 101
D Sieve Analysis Test 102
E Hydrometer Test 104
F Relative Density Test 106
G Standard Compaction Test 108
xi
H Falling Head Permeability Test 110
I Unconfined Compression Test 112
xii
LIST OF TABLES
Table No. Title
Page
1.1 Consumption rate for different types of plastics resin per day of the
respondent companies
4
1.2 Samples with Different Variables
8
2.1 General clay characteristics
12
2.2 Typical value of compression index of different type of soil offered
by Prof. Juan M. Pestana-Nascimento
14
2.3 Mechanical properties of the compaction
26
2.4 Range of Saturated Hydraulic Conductivity of Various Soil Material
30
2.5 Permeability value of PP to various gaseous
31
2.6 Comparison of the pressure response of similar semi-crystalline
polymers with different volume (room temperature)
32
2.7 Result of Unconfined Compression Test for group columns with
different height of columns
42
3.1 Summary of Laboratory Testing Program
45
3.2 Sample with variables of crushed PP installation
59
3.3 Summarization of the area replacement ratio calculations for 100
mm height of column
62
4.1 Basic properties of kaolin clay and PP
65
4.2 Specific gravity value for several type of soils
69
4.3 Type of soil with its unit weight
73
4.4 Permeability coefficient for different soils
74
4.5 Average value of shear strength for controlled sample
76
4.6 Average value of shear strength for reinforced column of 6 mm
diameter and 60 mm height
77
xiii
4.7 Average value of shear strength for reinforced column of 6 mm
diameter and 80 mm height
78
4.8 Average value of shear strength for reinforced column of 6 mm
diameter and 100 mm height
79
4.9 Average value of shear strength for reinforced column of 10 mm
diameter and 60 mm height
81
4.10 Average value of shear strength for reinforced column of 10 mm
diameter and 80 mm height
82
4.11 Average value of shear strength for reinforced column of 10 mm
diameter and 100 mm height
83
4.12 Summary of Analysis on Unconfined Compression Test
84
4.13 Effect of area replacement ratio for fully penetrating columns of
several studies
86
xiv
LIST OF FIGURES
Figure No. Title
Page
1.1 Installation of granular column
2
1.2 Consumption rate of plastics according to resin types
4
1.3 Unconfined Compression Test (UCT)
7
2.1 Quaternary Sediments in Peninsular Malaysia
11
2.2 The Relationship between Void Ratio, e and Log P for Normally
Consolidated and Overconsolidated Soil
13
2.3 Strength of Klang Clay
15
2.4 Crushed PP in pellet form
17
2.5 The Scanning Electron Microscopy photographs of PP powder
18
2.6 Particle size distribution of ELTEX P powders with different
grade
19
2.7 Particle size distribution between ELTEX P powder, other
commercial powders and group PP pellets
20
2.8 (a) SEM photomicrograph of morphology
(b) Particle size distribution of HPP-plastomer blend
21
2.9 (a) SEM photomicrograph of morphology
(b) Particle size distribution of HPP-EPR blend
22
2.10 (a) Comparison of specific gravities of fibres
(b) 1 kg of PP of equivalent coverage yields 20-41% more yarn
than other fibres, giving higher yield for the same weight
23
2.11 Effects on compaction on pore space
24
2.12 Moisture-density curve of soil for a given compactive effort
25
2.13 The effect of PP on shear strength of sand under normal load 28
kPa
29
xv
2.14 The effect of PP on the shear strength of the sand under three
different normal loads
29
2.15 Stone Column Installation
33
2.16 Effect of column height over column diameter ratio on
undrained shear strength
35
2.17 Column arrangement
36
2.18 Mechanisms of load transfer for (a) rigid pile and (b) a stone
column
37
2.19 Consolidation response for a group of columns
38
2.20 Excess pore pressure during consolidation
39
2.21 The variation of deviatoric stress and volumetric strain with
axial strain (a) Ac/As=7.9% (b) Ac/As=17.8% (c) Ac/As=31.2%
40
3.1 Flowchart of Project Methodology
44
3.2 Cone Penetration Method
47
3.3 Small pycnometers are leaved under vacuum
49
3.4 (a) Sieve shaker (b) Sieve analysis set
50
3.5 Equipment set up for the hydrometer test
51
3.6 Relative Density Test Equipment set up on vibrating table
52
3.7 The typical apparatus of the standard proctor test that are
standard compaction mold (left) and standard compaction
hammer (right)
54
3.8 The setup of apparatus for falling head test
55
3.9 Preparation of samples using customized mold
57
3.10 Drilling process of specimen
58
3.11 (a) Detailed arrangement of columns for diameter of 6 mm
(b) Detailed arrangement of columns for diameter of 10 mm
60
xvi
3.12 (a) 2D arrangement of columns with 6 mm diameter of PP
column
(b) 2D arrangement of columns with 15 mm diameter of PP
column
61
3.13 (a) Before installation of PP columns into the kaolin clay
(b) After installation of PP columns into the kaolin clay
62
3.14 Equipment set up for unconfined
63
4.1 Graph of penetration versus moisture content for liquid limit test
67
4.2 Plasticity Chart
68
4.3 Particle Size Distribution of Kaolin
70
4.4 Particle Size Distribution of PP
71
4.5 Dry unit weight versus average moisture content of kaolin
73
4.6 Relationship of strain and stress for controlled sample
76
4.7 Relationship of strain and stress for reinforced column of 6 mm
diameter and 60 mm height
78
4.8 Relationship of strain and stress for reinforced column of 6 mm
diameter and 80 mm height
79
4.9 Relationship of strain and stress for reinforced column of 6 mm
diameter and 100 mm height
80
4.10 Relationship of strain and stress for reinforced column of 10 mm
diameter and 60 mm height
81
4.11 Relationship of strain and stress for reinforced column of 10 mm
diameter and 80 mm height
82
4.12 Relationship of strain and stress for reinforced column of 10 mm
diameter and 100 mm height
83
4.13 Improvement of shear strength versus area replacement ratio,
Ac/As
85
4.14 Relationship of strain and stress for reinforced column of 6 mm
diameter with 60 mm, 80 mm and 100 mm height
87
xvii
4.15 Relationship of strain and stress for reinforced column of 10 mm
diameter with 60 mm, 80 mm and 100 mm height
87
4.16 Improvement of shear strength versus column penetration ratio,
Hc/Hs
88
4.17 Relationship of strain and stress for reinforced column of 6 mm
and 10 mm diameter with 60 mm height
89
4.18 Relationship of strain and stress for reinforced column of 6 mm
and 10 mm diameter with 80 mm height
90
4.19 Relationship of strain and stress for reinforced column of 6 mm
and 10 mm diameter with 100 mm height
90
xviii
LIST OF APPENDICES
Appendix Title
Page
A
Properties of Polypropylene 98
B Atterberg Limit Test
99
C Specific Gravity Test
101
D Sieve Analysis Test
102
E Hydrometer Test
104
F Relative Density Test
106
G Standard Compaction Test
108
H Falling Head Permeability Test
110
I
Unconfined Compression Test
112
xix
LIST OF SYMBOLS
Ac Area of column
As Area of sample
c Cohesion
Cc Compression index
Cc Coefficient of gradation
Cu Uniformity coefficient
e Void ratio
ε Strain
Gs Specific gravity
Hc Height of column
Hs Height of sample
i Hydraulic gradient
k Permeability coefficient
m Moisture content
Se Elastic settlement
Sc Primary consolidation settlement
Ss Secondary consolidation settlement
ST Total settlement
Pc Maximum pressure the soil has been subjected to in past
ρd Dry density
ρd-max
Maximum dry density
ρd-min Minimum dry density
xx
q Deviator stress
qmax Maximum deviator stress
Rd Relative density
So Sorting coefficient
su Undrained shear strength
v Velocity
γd Dry unit weight
γt Wet unit weight
γsat Saturated unit weight
φ Angle of internal friction
σ Normal stress
xxi
LIST OF ABBREVIATIONS
ABS Acrylonitryl Butadien Styrene
AASHTO
American Association of State Highway and Transportation
Officials
ASTM American Society for Testing and Materials
BS British Standard
BSCS British Soil Classification System
CL Clay low plasticity
CH Clay high plasticity
EPR Ethylene-propylene rubber
FYP Final Year Project
HDPE High-density polyethylene
HPP Homo-polymer Polypropylene
LL Liquid limit
LDPE Low-density polyethylene
MDPE Medium-density polyethylene
MH Silt high plasticity
ML Silt low plasticity
MPMA Malaysian Plastics Manufacturer Association
NP Non-plastic
PC Polycarbonate
PE Polyethylene
PI Plasticity index
xxii
PL Plastic limit
PP Polypropylene
PS Polystyrene
PT Peat
SL Shrinkage limit
UCT Unconfined Compression Test
USCS Unified Soil Classification System
CHAPTER 1
INTRODUCTION
1.1. BACKGROUND OF RESEARCH
Recently, due to urbanization and industrialization that increase the development,
the building construction such as housing and commercial are being built massively. Soft
clays exist in most coastal plains of Peninsular Malaysia and all land including soft soil has
to utilize to overcome the massive construction. Clay is widely distributed, abundant
mineral resources of major industrial importance for an enormous variety of uses (Ampian,
1985). Development of activities on those sites such as road embankment, earth dams and
others involve problems of stability and excessive settlement. There are many available
methods to improve the properties of soft clay soil since this type of soil usually causes
problems to the civil engineer as it has high compressibility and low shear strength.
The settlement behavior of soil must be understand to find the solution for it
because it may impose stability problem to the superstructure where the rate of settlement
is different all over the area of the developed ground if the uneven settlement occurred.
Uneven settlement might cause toppling of the said superstructure, meanwhile for uniform
settlement, foundation settlement problem can occur in excessive settlement (Halim, 2012).
Thus, settlement of soil must be solved before the superstructure being constructed.
Therefore, ground improvement techniques may be necessitated to modify the soil
properties. There are many available methods to improve the properties of soft clay such as
sand drain, piling, stone (granular) column, using admixtures and many more. Recently,
2
stone column are gaining acceptances in geotechnical field and have been widely used all
around the world including Malaysia. This method is applied commonly for road
embankments and railway area, lightly loaded foundation, and storage tanks (Murugesan
and Rajagopal, 2010). Besides it promotes the compaction of the soil and allows water to
rise up by acting as a channel, additional bearing capacity is also provided to the soil.
This Final Year Project (FYP) concentrates on the strength of soft clay reinforced
with group crushed Polypropylene (PP) columns. Basically, concept of crushed PP columns
with stone column is the same, but the result from this process is slightly different depends
on the properties of the PP itself. However, this ground improvement technique has been
successfully applied to reduce the settlement as well as increasing the bearing capacity of
the soils and accelerating the settlement process (Ambily and Gandhi, 2007).
Previous studies have been proven that when the granular column is inserted into
soft soil as shown in Figure 1.1, a composite soil mass that has a greater strength and
improved stiffness will be produced compared to the unreinforced soil. The columns act as
piles that transfer the structure load to greater depth. Thus, this is one of the most practical
techniques to improve the mechanical properties of soft soil (Black et al., 2007).
Figure 1.1: Installation of granular column
Source: Juan Manuel et al. (2010)
3
PP is a thermoplastic which means those materials can be melted again and again
and also can be heated to a certain temperature and will harden again as they cool. It has an
intermediate level of crystallinity which located between low-density polyethylene (LDPE)
and high-density polyethylene (HDPE). It is known for its low strength to density ratio
compared to HDPE and LDPE which the density can range from 0.90 to 0.92 g/cm3. PP
yields the greatest volume of fibre for a given weight because of its low specific gravity
which means that PP provides good bulk and cover while being lighter in weight. The
porous PP molecule has a series of CH3 groups that oriented on one side of the carbon
backbone which is making PP stiffer, creates higher degree of crystallinity and more
resistance to the tendency to flow under stress as compared to polyethylene (PE). It is also
harder and more opaque to withstand somewhat higher temperature up to 160 °C, or 320 °F
without melting.
The rapid economic growth in Malaysia has generated 0.5-08 kg waste
material/person/day and in rural areas the figure increased to 1.7 kg/person/day (Kathirvale
et al., 2003). The authors noted that plastics materials constitute the largest component of
waste material by weight at 18.9 %, apart from food and paper. Findings from study
indicated that plastics materials are disposed at rate of 2.943 kg/day, an approximation of 5
% from the daily consumption of plastics material. This finding is in agreement with the
results obtained by Rossbach (1979) at 5.3 %. The results from Malaysian Plastics
Manufacturer Association (MPMA) (2004) clearly indicated that polyolefin such as
polypropylene (27 %) and polyethylene (10 %) monopolized the plastics industry in
Malaysia and it reported that the consumption of poly olefins as the highest, at 67.7 %.
Figure 1.2 and Table 1.1 show the consumption rate for different types of plastics resin
(MPMA, 2004). Currently, the recycling and fully utilization of waste materials have
attracted great attention in construction field to fulfill the current interest in long term and
sustainable development, as well as to reduce the cost of managing the landfill.
4
Table 1.1: Consumption rate for different types of plastics resin per day of the respondent
companies
Plastic resin kg day-1
Polypropylene (PP) 12827
Polyethylene (PE) 4588
Polystyrene (PS) 9413
Polycarbonate 1825
Acrylonitrile butadiene styrene (ABS) 13218
Others 4966
Total consumption per day 46837
Source: Malaysian Plastics Manufacturers Association, MPMA (2004)
Figure 1.2: Consumption rate of plastics according to resin types
Source: Malaysian Plastics Manufacturers Association, MPMA (2004)
5
1.2. PROBLEM STATEMENT
Chen and Morriss (2000) stated that the design of foundation on soft clay has been
the concern of engineers since the beginning of soil engineering. Therefore, structures
constructed on soft soils may experience excessive settlements, large lateral flow and slope
stability (Abdullah and Edil, 2007). This has leads to the findings and applications of
various type of ground improvement, for example granular columns. This technique is
preferable because it gives the advantage of reduced settlements and accelerated
consolidation settlements due to reduction in flow path lengths. One of the major factors
that could lead to high settlement is the high compressibility properties of soft clay. This
condition due to finer particles of soft clay and the presence of water make it being too
cohesive. High settlement is so dangerous because it affects the movement of whole
structure and end up with structure failures.
Due to the rapid development of building construction and highway infrastructure,
the settlement of soft soil become one of the main problems for foundation design. For
example, there is an increase of stress in the soft ground as well as the strain or settlement
when a road embankment is constructed over soft ground. Excessive yielding in vertical
and lateral direction of the soft ground will occur if the surcharge load due to filling and
constructions traffic load is high near the ultimate bearing capacity of the supported soft
ground. Moreover, this situation will followed by tension crack, deep seated rotational or
translational slip when the deformation is large and extensive.
Therefore, in this study, the strength of soft soils reinforced with group crushed PP
as replacement material in granular column had been investigated. Expecting the analysis
result may give the positive progress to the soil improvement such as the undrained shear
strength of sample reinforced was greatly improved compared with that of the unreinforced
samples. Indirectly, it will solve the PP disposal problem by reusing the material to
reinforce the soft soils, besides, the landfill in Malaysia also have been limited due to the
increasing of daily waste. Furthermore, since the PP is a waste material, the cost of soil
6
improvement can be reduce and hopefully the analysis result will help to make further
progress to the soil improvement of the soft clay.
1.3. OBJECTIVES
The aim of this study is to investigate the strength of soft clay reinforced with group
crushed PP columns. The soft clay has been represented by compacting kaolin paste. This
study is carried out to achieve the objectives as follow:
i. To determine the physical characteristics of kaolin clay and PP and
morphological characteristics of PP;
ii. To determine the undrained shear strength of soft clay reinforced with
various dimensions of group PP columns.
1.4. SCOPE OF STUDY
The materials used in this study were kaolin as soil sample and crushed PP as
reinforcing columns. To determine the physical properties of kaolin and PP and the
morphological characteristics of PP, the following laboratory tests were carried out:
i. Atterberg Limit Test
ii. Specific Gravity Test
iii. Sieve Analysis Test
iv. Hydrometer Test
v. Relative Density Test
vi. Standard Compaction Test
vii. Falling Head Permeability Test