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ENHANCED SHEAR RESISTANCE OF RAILTRACKS WITH
BALLAST-RUBBER COMPOSITES: A LABORATORY STUDY
SITI FARHANAH BINTI S.M JOHAN
A dissertation project submitted in partial fulfilment of the requirement for the
award of the degree in Master of Science in Railway Engineering
CENTRE FOR GRADUATE STUDIES
UNIVERSITI TUN HUSSEIN ONN MALAYSIA
2015
v
ABSTRACT
Railway ballast, which form an integral part of rail tracks, are highly susceptible to
subsistence due to both vibration transmitted by the passing trains, as well as the
influence of the weathering and contamination effect. The resulting subsistence
necessitates regular monitoring and maintenance, involving cost and time consuming
remedial actions, such as stone-blowing and ballast renewal. It would be desirable if
some measure can be taken in minimize the maintenance costs of railway tracks,
consequently to optimizing the passenger comfort. This paper describes the
exploratory work on ballast-rubber composites to enhanced the shear resistance of
rail tracks and identify the effects of ballast exposure to the weathering and oil
contamination. The rubber elements were sourced from tyre inner tubes commonly
used for motorcycles, cut and shaped accordingly to produce strips, shreds and
circular patch respectively and were arranged in various pre-determined
configurations within the ballast layer. Granitic stones of suitable sizes were sieved
and used as representative samples of typical ballasts as the tests were mainly carried
out with a standard direct shear test setup, i.e. shear box measuring 60 mm x 60 mm.
In order to identify the shear resistance deterioration of aggregate-rubber mixture
under poor drainage conditions by soaked a batch of aggregates in water, acid and
lubricant oil to create the effect from moisture and contamination for 14 days prior to
mixing and testing. The direct shear test results indicated that rubber inclusion could
effectively improve the shear resistance of ballasts to various degrees, though the
configurations clearly played an important role in the improvement observed. Both
type of rubber (i.e. new and used), show similar result due to the degradation of used
rubber tube does not too extensive. The shear resistance did not rise dramatically
with the rubber reinforcement. This susceptible shear strain plots indicate ductile
behaviour on the aggregates-rubber composites. This is evident by the linear rise of
shear stress with strain up to approximately 10 % for the control samples (CS) until
it reaches a constant value. Note that all the specimens including CS are in a loose
state during the testing because there were no tamping been applied on the samples.
Overall the circular patch (CP) specimen was the most favourable in all conditions
vi
(dry, acid and oil). At ε = 5%, CP (D) already governed the τave with 170 kPa than
the others. In addition, the friction angle for all configurations (dry, acid, oil) was in
the ranged 87◦- 88
◦ with the critical specific volume, vcrit was 2.160. It was followed
by the ST (H), which was found to allow better deformation capability with
increased ductility of the composite, while the shreds (SH) absorbed impact and
reduced breakages of the ballasts. Both mechanisms contributed to the reduced
overall subsistence, accompanied by an increase in the shear resistance. The
inclusion of rubber elements apparently prevented the dilation of the granular
material when approaching the shear failure and the reducing the settlement.
vii
ABSTRAK
Balast keretapi, merupakan sebahagian daripada infrastruktur landasan kereta api. Ia
sangat terdedah pada kerosakan disebabkan daripada getaran dari keretapi berlalu,
serta balast akan pecah apabila beban dikenakan berulangan serta pengaruh dari
cuaca dan kesan pencemaran terutamaya dari minyak yang tertumpah dari gearabak
kerata api.. Maka, pemantauan secara berkala amat diperlukan dan kekerapan
penyelenggaraan bertambah yang akan melibatkan kos yang tinggi serta makan masa
untuk pemulihan. Antara contoh penyelenggaraan dan pemulihan landasan keretapi
seperti „stone-blowing’dan pembaharuan balast. Ianya sangatlah wajar jika terdapat
langkah-langkah yang boleh diambil untuk mengurangkan haus dan lusuh daripada
kesan lalu lintas kereta api untuk memanjangkan jangka hayat balast. Kajian ini
bertujuan untuk mengetahui penggunaan elemen getah dalam tangani masalah ini
serta keaadan batu yang berbeza. Elemen getah digunakkan adalah daripada tiub
motosikal yang dipotong dan dibentukkan dengan sewajarnya untuk menghasilkan
pelbagai konfigurasi untuk kajian ini. Batuan granite dengan saiz yang sesuai telah
disaring dan digunakan sebagai sampel yang mewakilikan balast biasa telah banyak
dijalankan dengan kaedah kotak ricih yang berukuran 60 mm x 60 mm. Bagi
mengenal pasti kebolehkerjaan dengan campuran batu-getah akan direndam asid dan
minyak pelincir untuk mewujudkan kesan dari kelembapan dan pencemaran selama
14 hari sebelum pencampuran dan ujian. Tiub getah dipotong dan dicincang dengan
sewajarnya untuk menghasilkan jalur dan corak-carik masing-masing, dan telah
disusun dalam pelbagai konfigurasi yang telah ditentukan dalam lapisan balast.
Keputusan ujian ricih langsung menunjukkan bahawa penggunaan getah amat
berkesan dengan meningkatkan rintangan ricih balast untuk pelbagai darjah, dengan
susunan sampel. Ia juga memainkan peranan penting dalam peningkatan yang
diperhatikan. Ini dapat dilihat dengan peningkatan tegasan ricih dengan tekanan
sehingga kira-kira 10% bagi CS sehingga ia dalam nilai yang tetap. Tambahan
bahawa semua sampel termasuk CS berada dalam keadaan longgar semasa ujian.
Keseluruhan kajian ini menunjukkan bahawa CP adalah contoh yang paling baik
dalam semua keadaan (kering, asid dan minyak). Pada ε = 5%, CP (D) telah ditadbir
viii
τave dengan 170 kPa daripada yang lain. Di samping itu, sudut geseran untuk semua
konfigurasi (kering, asid, minyak) adalah 87◦- 88
◦ dengan specific volume, vcrit adalah
2.160. Ia diikuti oleh ST (H), didapati berkeupayaan untuk ubah bentuk yang lebih
baik dengan kemuluran meningkat daripada komposit, manakala corak-carik (SH)
memberi kesan penyerapan impak terhadap pepecahan terhadap balast dapat
dikurangkan. Keseluruhan dalam kajian ini mendapati bahawa membenarkan
keupayaan ubah bentuk dengan kemuluran yang meningkat, Kedua-dua mekanisme
ini telah menyumbangkan kepada penggurangan sara hidup secara keseluruhan, ia
juga telah meningkatan rintangan ricih.
ix
CONTENTS
ACKNOWLEDGEMENTS iv
ABSTRACT v-vi
ABSTRAK vii-viii
LIST OF TABLES xii
LIST OF FIGURES xiii-xv
LIST OF EQUATIONS xvi
LIST OF SYMBOLS xvii
LIST OF APPENDICES xviii-xix
CHAPTER 1 INTRODUCTION
1.1 General 1-6
1.2 Problem Statement 6-7
1.3 Scope of Study 8
1.4 Aim and Objectives 9
1.5 Significance of Study 9
1.6 Organisation of the Dissertation 10
1.7 Summary 10
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction 11
2.2 Rail track
2.2.1 Track Components 11-13
2.2.2 Track Forces 13-14
2.2.3 Track Maintenance 14-15
2.3 Ballast
2.3.1 Ballast Properties 16
2.3.2 Functions of Ballast 17
2.3.3 Ballast Specification and Testing 17-18
2.3.4 Ballast Degradation and Fouling 18-19
2.4 Particle Breakage on Aggregates 19-21
2.5 Ballast Contamination 22-23
2.5.1 Acid rain effect 23-24
x
2.5.2 Lubricant oil effect 24-25
2.6 Rubber Tyres 25-26
2.6.1 Rubber tubes 27-28
2.6.2 Shredded Tyres 29
2.6.3 Strip rubber 30
2.6.4 Crumb rubber 30-31
2.7 Shear stress-strain relationship
2.7.1 Shear stress 31
2.7.2 Shear strain 31-32
2.7.3 Stress-strain relationship for aggregates 32-33
2.8 Shear strength of granular materials 33-34
2.9 Shear strength for granular-rubber mixtures 34-35
2.10 Summary 35-36
CHAPTER 3 RESEARCH METHODOLOGY
3.1 Introduction 37-38
3.2 Raw materials
3.2.1 Ballast aggregates 39
3.2.2 Rubber tube 40
3.2.3 Hydrochloric acid (HCL) 41-42
3.2.4 Lubricant oil 42-43
3.3 Physical properties tests
3.3.1 Particle size distribution 43-45
3.3.2 Specific gravity 45
3.3.3 Particle shape 46-47
3.3.4 Aggregates impact value 47-48
3.4 Methodology
3.4.1 Preparation of aggregates 48-49
3.4.2 Preparation of rubber elements 50-52
3.4.3 Direct shear test 53-57
3.5 Summary 57-58
xi
CHAPTER 4 RESULTS AND DISCUSSIONS
4.1 Introduction 59
4.2 Physical properties of material 60
4.2.1 Particle size distribution 60-62
4.2.2 Specific gravity 62
4.2.3 Aggregates shape (flakiness & elongation index) 63
4.2.4 Aggregates impact value (AIV) 63-64
4.3 Particle breakage 64-65
4.4 Direct shear test
4.4.1 Comparison between new and used rubber tube 65-71
4.4.2 Comparisons between all configurations for dry 71-81
specimens
4.4.3 Comparisons between all configurations for acid 82-90
specimens
4.4.4 Comparisons between all configurations for oil 91-99
specimens
4.4.5 The effect of moisture and contamination 100-101
4.5 Summary 102
CHAPTER 5 CONCLUSIONS AND RECOMMENDATION
5.1 Conclusion 103-104
5.2 Recommendations 104
REFERENCES
APPENDICES
VITA
PUBLICATIONS
xii
LIST OF TABLES
2.1 The specification for ballast particle size distributions 18
3.1 Properties of HCL 39
3.2 Details of configurations 49
4.1 Observation data from dry sieving 57
4.2 Result of specific gravity 58
4.3 Summary of flakiness and elongation index 59
4.4 Summary of Aggregates Impact Value (AIV) 60
4.5 Summary of data for CS (D), NRT (D) and URT (D) specimens 70
4.6 Summary of ɛ =5% corresponding τave for dry specimens 73
4.7 Summary of data for dry specimens in all configurations 81
4.8 Summary of ɛ =5% corresponding τave for acid specimens 83
4.9 Summary of data for acid specimens in all configurations 90
4.10 Summary of ɛ =5% corresponding τave for oil specimens 92
4.11 Summary of data for oil specimens in all configurations 99
4.12 Summary of failure envelope for all configurations 101
4.13 Summary of friction angle for all configurations 101
xiii
LIST OF FIGURES
1.1 ETS KTM at KL Sentral Station 2
1.2 KLIA Express at Salak Tinggi Station 2
1.3 KL Monorail at Bukit Nanas Station 3
1.4 LRT Rapid KL at Kelana Jaya Station 3
1.5 Typical infrastructure for ballasted track 4
1.6 Rail track Infrastructure 4
1.7 Rail track infrastructure 5
1.8 Tracks fouls due to ballast degradation and contamination 6
2.1 Typical of railway track components 12
2.2 Principle of track structure for longitudinal structure 12
2.3 (a) Layout of track forces 14
2.3(b) Layout of track forces 14
2.4 Stone blowing wagon 15
2.5 Fouling ballast 19
2.6 Ballast breakage index (BBI) calculation method 21
2.7 Shape of ballast particle changes after the force contact 21
2.8 Ballast contamination due to clay pumping in Ashfield,
New South Wales, Australia 23
2.9 Ballast contamination due to coal contamination in
Rockhampton, Queensland, Australia 23
2.10 Ballast gravels contaminated by lubricant oil 25
2.11(a) Structure of tyres 25
2.11(b) Component of tyre 25
2.12 Structural comparison of tube and tubeless 28
2.13 Rubber inner tube 28
2.14 Rubber shreds 29
2.15 Strip rubbers 30
2.16 Crumb rubber 31
2.17 Shear stress –strain relationship 32
xiv
2.18 Shear plane for granular particles in shear box 34
3.1 Methodology flow chart 36
3.2 Aggregates for direct shear test (6.3 mm) 37
3.3 Rubber tube 38
3.4(a) Hydrochloric acid (HCL) 40
3.4(b) Apparatus and chemical for diluting concentrated HCL 40
3.5 Acid preparation 40
3.6 Mechanical sieve machine 43
3.7 Aggregate impact test apparatus 46
3.8 Specimens of aggregates (gravels) 47
3.9 Configurations of rubber tube 48
3.10 Illustration for ST with gravels in shear box 49
3.11 Illustration for SH with gravels in shear box 50
3.12 Illustration for CP with gravels in shear box 50
3.13 Mohr-Coulomb failure envelope 52
3.14 Direct shear machine and instruments 52
3.15 Rubber inclusions in various configurations 53
4.1 Particle size distribution of ballast aggregates used in DST 62
4.2(a) Stress-strain curves 67
4.2(b) Vertical-horizontal displacement of dry specimens for
NRT (D) and URT (D) 67
4.3 (a) Volumetric strain, ɛvol - shear strain, ɛ of dry specimens for
NRT (D) 68
4.3 (b) Volumetric strain, ɛvol - shear strain, ɛ of dry specimens for
URT (D) 68
4.4 (a) Specific volumes, v-shear strain, ɛ of dry specimens for
NRT (D) 69
4.4 (b) Specific volume, v-shear strain, ɛ of dry specimens for
URT (D) 69
4.5 Failure envelopes for CS (D), NRT (D) and URT (D) specimens 70
4.6 Sketches of specimens based on results from Table 4.6 72
4.7 Sketch of the aggregates movement (dilation) 74
xv
4.8 Sketches of the aggregates rolls over during shearing 74
4.9 (a) Stress – strain, (b) Vertical-horizontal displacement for CS (D) 74
4.10 (a) Stress – strain, (b) Vertical-horizontal displacement for ST(V)_D 75
4.11 (a) Stress – strain, (b) Vertical-horizontal displacement for ST(H)_D 75
4.12 (a) Stress – strain, (b) Vertical-horizontal displacement for SH(C)_D 76
4.13 (a) Stress – strain, (b) Vertical-horizontal displacement for SH(F)_D 76
4.14 (a) Stress – strain, (b) Vertical-horizontal displacement for CP_D 77
4.15 Volumetric strain-shear strain for dry specimens in all configurations 78
4.16 Specific volume, v for dry specimens in all configurations 79
4.17 Failure envelope for dry specimens in all configurations 80
4.18 Sketches of specimens based on results from Table 4.8 82
4.19 (a) Stress – strain plot, (b) Vertical-horizontal displacement for CS (A) 84
4.20 (a) Stress – strain plot, (b) Vertical-horizontal displacement for ST (V) 85
4.21 (a) Stress – strain plot, (b) Vertical-horizontal displacement for ST (H)_A 85
4.22 (a) Stress – strain plot, (b) Vertical-horizontal displacement for SH (C)_A 86
4.23 (a) Stress – strain plot, (b) Vertical-horizontal displacement for SH (F)_A 86
4.24 (a) Stress – strain plot, (b) Vertical-horizontal displacement for CP_A 87
4.25 Volumetric strain-shear strain for acid specimens in all configurations 88
4.26 Specific volume (v)-shear strain for acid specimens in all configurations 89
4.27 Failure envelope for acid specimens in all configurations 90
4.28 Sketches of specimens based on results from Table 4.10 93
4.29 (a) Stress-strain plot, (b) Vertical-horizontal displacement for CS_O 93
4.30 (a) Stress – strain plot, (b) Vertical-horizontal displacement for ST(V)_O 94
4.31 (a) Stress – strain plot, (b) Vertical-horizontal displacement for ST(H)_O 94
4.32 (a) Stress – strain plot, (b) Vertical-horizontal displacement for SH(C)_O 95
4.33 (a) Stress – strain plot, (b) Vertical-horizontal displacement for SH(F)_O 95
4.34 (a) Stress – strain plot, (b) Vertical-horizontal displacements for CP_O 96
4.35 Volumetric strain-shear strain for oil specimens in all configurations 97
4.36 Specific volume (v)-shear strain for oil specimens in all configurations 98
4.37 Failure envelope for oil specimens in all configurations 99
xvi
LIST OF EQUATIONS
2.1 Ballast Breakage Index (BBI) 20
2.2 Shear Strength 33
3.1 Molarity of Chemicals 39
3.2 Uniformly Coefficient 42
3.3 Coefficient of Curvature 42
3.4 Mass Passing 42
3.5 Cumulative Percentage Passing 42
3.6 Specific Gravity 43
3.7 Flakiness Index 44
3.8 Elongation Index 45
3.9 Aggregates Impact Value 45
3.10 Shear Failure 51
3.11 Shear Stress 52
4.1 Young’s Modulus 62
4.2 Poisson’s Ratio 63
4.3 Volumetric strain, ɛvol 64
4.4 Shear strain, ɣ 64
4.5 Specific volume, v 64
xvii
LIST OF SYMBOLS
LRT Light Rail Transit
ERL Express Rail Link
KTM Keretapi Tanah Melayu
KL Kuala Lumpur
ROW Right of Way
KLIA Kuala Lumpur International Airport
BS British Standard
AREMA American Railway Engineering and Maintenance
ASTM American Standard Testing Method
PSD Particle Size Distribution
BBI Ballast Breakage Index
pH Water Properties
HCL Hydrochloric Acid
Cu Uniformly Coefficient
Cc Coefficient of Curvature
Gs Specific Gravity
τ Shear Stress
ɣ Shear Strain
ɛ Strain
ϕ Friction Angle
σ Total Stress
∆h Horizontal Displacement
∆v Vertical Displacement
CS Control Samples
ST Strips
SH Shreds
CP Circular Patch
kPa KiloPascal
R2
Regression
CL Cross Line
xviii
LIST OF APPENDICES
A 1-1 Graph for shear stress-strain for dry specimens
(All configurations) (used tube rubber)
A1-2 Graph for shear stress-strain for acid specimens
(All configurations) (used tube rubber)
A 1-3 Graph for shear stress-strain for oil specimens
(All configurations) (used tube rubber)
B 1-1 Graph of failure envelope for dry specimens
(All configurations) (used tube rubber)
B 1-2 Graph of failure envelope for acid specimens
(All configurations) (used tube rubber)
B 1-3 Graph of failure envelope for oil specimens
(All configurations) (used tube rubber)
C 1-1 Graph of volumetric strain-shear strain for dry specimens
(All configurations) (used tube rubber)
C 1-2 Graph of specific volume-shear strain for dry specimens
(All configurations) (used tube rubber)
C 1-3 Data of volumetric strain and specific strain for dry specimens
(All configurations) (used tube rubber)
D 1-1 Graph of volumetric strain-shear strain for acid specimens
(All configurations) (used tube rubber)
D 1-2 Graph of specific volume-shear strain for acid specimens
(All configurations) (used tube rubber)
D 1-3 Data of volumetric strain and specific strain for acid specimens
(All configurations) (used tube rubber)
E1-1 Graph of volumetric strain-shear strain for oil specimens
(All configurations) (used tube rubber)
E 1-2 Graph of specific volume-shear strain for oil specimens
(All configurations) (used tube rubber)
E 1-3 Data of volumetric strain and specific strain for oil specimens
(All configurations) (used tube rubber)
xix
F 1-1 Data from direct shear test for dry specimens
(All configurations) (used tube rubber)
F 1-2 Data from direct shear test for acid specimens
(All configurations) (used tube rubber)
F1-3 Data from direct shear test for oil specimens
(All configurations) (used tube rubber)
CHAPTER 1
INTRODUCTION
1.1 General
Railway line in Malaysia has been upgraded either in their system or infrastructure in
order to parallel with the country development. Based on Lowtan (2004), there are
several railway transport services in Malaysia such as heavy rail, express rail link
(ERL), light rail transit (LRT) and monorail shown in Figure 1.1, 1.2, 1.3 and 1.4.
Lowtan (2004) mentioned that Keretapi Tanah Melayu (KTM) is the only
heavy rail operator in Malaysia providing services for passengers and freight. ERL
is the high speed train in Malaysia which link between KL Sentral and the Kuala
Lumpur International Airport (KLIA). Only the KTM and ERL provide ballasted
track along the route as their right of way (ROW). Meanwhile, LRT and monorail
could be found in the urban area and both services have their own concrete structure
as their route (Lowtan, 2004).
2
Figure 1.1: ETS KTM at KL Sentral Station (www.ktmb.com.my, 2015)
Figure 1.2: KLIA Express at Salak Tinggi Station (malaysiagazette.com, 2015)
3
Figure 1.3: KL Monorail at Bukit Nanas Station (Molon A., 2015)
Figure 1.4: LRT Rapid KL at Kelana Jaya Station (Schwandal R., 2007)
The rail track infrastructure shown in Figures 1.5, 1.6 and 1.7 are termed
ballasted track. The superstructure consists of rail, fastening, sleeper and it acts as
the main function in the rail track foundation (Bonnett, 2005). The substructure such
as ballast, subballast and subgrrade provides a foundation layer to support the
superstructure. Indraratna et al. (2007) also pointed out that the superstructure attains
optimum performance by transmitting the traffic load to the subgrade via the
substructure.
4
Figure 1.5: Typical infrastructure for ballasted track (Dahlberg, 2004)
Figure 1.6: Rail track Infrastructure (Depot KTM Gemas, 2013)
5
Figure 1.7: Rail track infrastructure (Station in KTM Gemas, 2013)
The term „ballast‟ used in railway engineering refers to the coarse aggregates
above the subballast layer and subgrade. Studies carried out by Bhanitiz (2007) and
Indraratna et al. (2001) reported on the behaviour of ballast deformation and
breakage under static and dynamic loading. Khabbaz and Indraratna (2009) also
found ballast to break down under the cyclic load from heavy trains as shown in
Figure 1.8.
As summarised by Selig and Waters (1994), vertical and horizontal
movements caused by traffic loads are attributed mainly to the deformation and
densification of the ballast. Rail track performance depends on the ballast as the
main material and leads to poor ride quality, requiring either speed restrictions or
maintenance to realign the tracks (Anderson and Key, 2000).
Ballast has to be tough, dense, weather-resistant and mechanically stable
(Dahlberg, 2004). Generally, rail track ballast is exposed to the dry and wet weather,
as well as the contamination caused by the braking wheels and oil leak from the
train. There could lead to negative effects on the rail track performance. Thus, it is
very important to ensure the quality and durability of ballast from such deterioration.
6
Figure 1.8: Tracks fouls due to ballast degradation and contamination
(ARTC, 2015)
1.2 Problem statement
In railway engineering, ballast play a crucial part in transmitting and distributing the
wheel load to the rail track foundation as well as support the rails and sleepers
(Indraratna et al., 2007). Ballast are highly susceptible to subsistence due to both
vibration transmitted by the passing trains, as well as the breakage of the ballasts
themselves with repeated impact. Based on conventional triaxial tests, Janardhanam
and Desai (1983) concluded that the particle size of ballast significantly affect the
overall resilient modulus, volumetric and shear behaviour. It follows that track
settlement is very much dependent on the ballast quality and its response to traffic
load.
Tennakoon et al. (2014) stated that contamination on ballast layer influence
the conditions of its drainage and shear strength. This contamination could decrease
an overall shear strength and impede the drainage of the track. According to
Khabbaz and Indraratna (2009), the main factors on ballast breakage that related to
the particles and loading conditions as example the confining pressure, ballast
7
gradation, presence of water or ballast moisture, dynamic loading pattern and the
frequency.
Ballast is able to allow the track misalignment caused by from the lateral
movement from the passing trains on curved track (Lam and Wang, 2001). In
addition, weather and water also could cause damage and crushing of ballast by axle
weight. The damage on ballast will lead to tracks “pumping” with the train‟s
passing, which eventually causes damage to the rail or sleepers (Railway Technical,
2014). Track “pumping” is a continuous loop of ballast and subgrade movement
which creates on up -down motion. This affects the comfort of passengers on board
as well as imposing additional wear on the rolling stock (Esveld, 2001). Fouling is
the proven ballast when it starts to damage, contamination, gradation changes and
performance reduction to suffer form. This condition affects the ballast size
distribution under the sleepers in certain areas along the rail track, resulting in
uneven support of the rail tracks (Siddique and Naik, 2004).
Degradation of ballast also contributes to increase frequency of maintenance
and rehabilitation cost too. It would be desirable if measures could be taken to
minimize the wear and tear effect of the rail traffic, consequently prolonging the life
span of the ballast. This because the wear and tear on the ballast could increase the
maintenance cost by realign the rail, replacement of tracks. Khabbaz and Indraratna
(2009) highlighted that the main causes of ballast degradation include excessive
dynamic loading, vibration, temperature, moisture fluctuation and impact load from
severe braking.
Rubber Manufacture Association (2006) had reported that discarded rubber,
especially waste tyres significantly increased the volume of solid waste. Some of
these rubber tyres and tube are left stockpiled in landfills or illegally dumped and
this could be harmful to the environment. It results in environmental hazards
worldwide and has indeed become a serious problem in many countries. The
quantity of used tyre can be beneficially used in geotechnical applications because
8
the tyres do not decompose and it is susceptible to fire hazards (Vinot and Singh,
2013).
1.2 Scope of study
This study is an exploratory work on the ballast-rubber tube composites
which involves measurements with the direct shear test. The rubber inclusions are
incorporated in the specimen in various configurations. The use of new inner tube as
the rubber elements was to ensure the consistency of the specimen tested.
Rail track ballast regularly exposed to the weather and oil contamination. Oil
contamination could happen due to the fuel leak and friction from wheel braking.
Simulations of the ballast with these conditions were achieved by submerging the
ballast with water, acid and lubricant oil for two weeks (14 days). A total of 132
specimens were tested:
i) Control sample (dry, wet, acid and lubricant oil)
ii) Dry aggregates + rubber tube (new and used)
iii) Wet aggregates + rubber tube (new and used)
iv) Hydrochloric acid aggregates + rubber tube (new and used)
v) Lubricant oil aggregates + rubber tube (new and used)
The shear box test was conducted on specimen of various configurations
such as coarse and fine shreds, vertical and horizontal strips and circular patch,
where three vertical stresses were applied respectively for each specimen.
9
1.4 Aim and objectives
The ultimate goal of this study is to verify that rubber inclusion could be more
effectively improve the shear resistance in ballast layer with various configurations.
The objectives for this research work are:
a) To determine the shear resistance of ballast aggregates with rubber inclusions
in various configurations through direct shear test.
b) To identify the effect of simulated exposure to moisture, acid and oil
contamination on the composite material (ballast-rubber mix).
1.5 Significance of study
The importance of this study is to determine the potential of rubber inclusions in
increasing the shear resistance of ballast aggregates in several predetermined
configurations. By having the rubber inclusion in the ballast layer, shear resistance
could be increased, consequently reducing the wear and tear for better and longer
performance.
Considering the cost-effectiveness, availability and practicality of ballast,
advancement in railway technology would arguably outrun the material substitution
or total replacement in the near future (Eisenmann, 1995). The rubber inclusion
could also enhance the shear resistance under exposure to the effects of chemical
attack and natural weathering. However, analysis of the composite‟s performance
under dynamic load was carried out too by adopting a number of empirical
correlations from part related work. In this study, only static test was conducted on
the ballast-rubber composites.
10
1.6 Thesis outline
Outline of this dissertation is summarized as follows. Chapter 1 presents the
problem statement, objectives and scope of the study. Chapter 2 presents the
literature review on the project, which included the background and significance of
the ballast aggregates as the part of railway track components and the properties of
materials. It also includes reviews on the rubber inclusion with granitic aggregates
and granular materials by using the standard direct shear box.
Chapter 3 presents details of the measurements and tests for collecting the
laboratory test results. Chapter 4 analyses and the results mainly from shear box
test. The discussions include assessment from the results obtained. Chapter 5
presents the conclusions and recommendation for future work.
1.7 Summary
This chapter highlights the general background of this study, including the aims and
objectives of the research, followed by an outline of the thesis.
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
This chapter presents a literature review related to ballast and rubber elements. This
literature review focuses on the following sections:-
a. Ballast and the rail track environment
b. Particle breakage and the associated with the ballast degradation
c. Ballast contamination
d. Rubber elements and its related functions
e. Shear strength associated with granular materials and rubber mixtures
2.2 Rail track
2.2.1 Track components
Railway track were laid down since in eighteenth century which was wagon that
used for carried collieries and quarries (Bonnett, 2005). Since then lot of invention
had been made in the railway engineering till now especially for railway tracks and
their infrastructures. Components in railway track are dividing by two main
components such as superstructure and substructure. Superstructure normally
consists of rails, sleepers, rail pads and fastening. Meanwhile for substructure
components consists of ballasts, sub-ballast and subgrade layered as shown in Figure
2.1 and 2.2 for typical components in railway track.
12
Figure 2.1: Typical of railway track components (Esveld, 2001)
Figure 2.2: Principle of track structure for longitudinal structure (Esveld, 2001)
The rails made from the steel girders that carried the axle load of train
(Bindra, 1976). Therefore, the material for rails should be required in qualities of
strength, fatigue endurance, wear and the resistance in corrosion (Bonnett, 2005).
The functions of rails were to distribute the wheel load from train and transfer it to
the sleepers system then to the substructure system. Fastening system for rails was
between rails and sleepers in order to resists the forces from vertical, lateral,
longitudinal and overturning movements of the rails (Wee, 2004).
Meanwhile, the sleepers which in monobloc shape is to spread the wheel
loads to ballast then transmits the lateral and longitudinal forces also functions to
hold the rails gauge and inclination (Bonnett, 2005). Subgrade is the last support to
sustain and distribute the resultant downward dynamic loading along its infinite
13
depth (Wan Azlan, 2012). According to Bhanitiz (2007), subgrade was the track
foundation which from the existing natural soil and also similar with other
foundation behaviour that has excessive settlement should be avoided. Li and Selig
(1995) mentioned that the excessive track settlement is generally due to the
accumulated plastic deformation of ballasts and substructures layers. However, this
gradual accumulation of permanent strains with traffic loads is often overlooked as
dynamic records often show negligible elastic deformation of the track support
system, where only static measurements reveal the accrued plastic strains (Yoo and
Selig, 1979). Furthermore, Dwyer-Joyce et al. (2003) simulated rail-wheel contact
with ballast and found that crushed ballast do not only indent and roughen the metal,
but inadvertently increase the traction level and reduce the residual fatigue life of the
contact.
2.2.2 Track forces
According to Bhanitiz (2007), the railway track has some forces such as vertical,
lateral and longitudinal directions act on the track structure due to the movement
traffic and the changing temperature. The acceleration and braking from the trains
had created the longitudinal forces and gave the thermal expansion or contraction of
the rails.
While for lateral forces, Bhanitiz (2007) had stated that lateral forces usually
comes from the lateral wheel force because of the friction between rail and wheel.
As shown in Figure 2.3 (a) and (b), vertical forces can be subdivided into downward
and upward force. Wan Azlan (2012) stated that railway track structures is primarily
analysed and over designed by considering the static and dynamic loads on the track
structures is to avoid from the excessive loading which could induce damage to the
railway foundation..
14
Figure 2.3 (a): Layout of track forces (Bhanitiz, 2007)
Figure 2.3(b): Layout of track forces (Bhanitiz, 2007)
2.2.3 Track maintenance
The railway track should have some maintenance in order to provide good
performance and comfort to the train passengers. The track ballast in railway system
exists for more than 150 years in the railway industry and it has become the basic
thing in track design (Edwards, 1990).Therefore, the maintenance usually takes plan
in one to three years.
According to Dahlberg (2004), because of the settlement of railway tracks,
regular maintenance work is necessary, for rail tracks without proper maintenance
could dangerous, such as resulting in train derailment.
15
Maintenance techniques had reached the high standard of development with
adoption of mechanization in most of the operations (Edwards, 1990).The
maintenance for the railway track have two methods such as tamping and
stoneblowing, as shown in Figure 2.4. The frequency of maintenance the track based
on the frequency of train runs in a year. It depends on the defects on the rail track
and the foundation. Due to the new technology, the defects or deformation on the
track can be detect by using the track circuit which transfer the information to the
control room operators to make the action.
According to Khabbaz and Indraratna (2009), there are two types of track
such as slab track and ballasted track. For slab track, it can be more effective in the
cost when the life-cycle maintenance were considered. Slab track also could provide
some advantages such as free of maintenance, less traffic disruption and no dust
emission. However, this type of track may not be favourable due to the high cost in
construction. As such, ballast track is still widely used due to its effectiveness,
efficiency and relatively easy maintenance.
Figure 2.4: Stoneblowingwagon (www.harsco.com)
16
2.3 Ballast
2.3.1 Ballast properties
In railway track components, ballast is the most important for the track that placed
on top of the track subgrade in order to support the weight of track structure and the
dynamic loading from passing trains. Usually ballast providing tensionless elastic
support, a free-draining coarse aggregate layer typically composed of crushed stones,
gravel and crushed gravel (Wan Azlan, 2012).
According to Pires and Dumont (2013), the depth of ballast structure in rail
track is 300-500 mm. Ballast should in angular shape of gravel that has granular
fractions between 22 mm and 63 mm. Materials for the ballast mostly include
dolomite, rheolite, gneiss, basalt, granite and quartzite which is composed of
medium to coarse gravel sized aggregates (Indraratna et al., 2007). Ballast is made
up of stones from granites or a similar that should be rough in shape to improve the
locking of stones. In Malaysia, granite is commonly used as track ballast, as can be
seen at KTM and ERL operations.
Good quality materials for railway ballast are angular shape, high specific
gravity, high shear strength, high toughness and hardness. The high resistance to the
weathering, rough surface and minimum hairline cracks also important properties of
railway ballast (Khabbaz and Indraratna, 2009). The important elements in the
railway track that related to the mechanical and hydraulic properties also the
efficiency in the maintenance.
17
2.3.2 Functions of ballast
Based on Selig and Waters (1994), Mundrey (2000), Esveld (2001), Dahlberg
(2003), Kaewunruen and Remennikov (2008), the fundamental functions for ballast
in railway track engineering can be summarised as follows:-
(a) Provides and resists vertical, lateral and longitudinal forces stability to track.
(b) Distributes the load from sleepers in order to resist the subgrade from high
stresses so that there will not have permanent settlement occur on track.
(c) Ballast also could absorb the shock from dynamic loading by providing
resilience bed for sleeper.
(d) Facilitate water drainage flow from track structure.
(e) It also gives easy maintenance surfacing and lining operations.
(f) Protects formation against rains and winds.
(g) Protect the sleepers form capillary moisture of structure.
(h) It can slow the vegetation growth and the fouling effect can be resist from
surface-deposited materials.
(i) Reduce bearing stresses from the sleepers to acceptable stress levels for
underlying layers
(j) Allow optimum global and local settlement
2.3.3 Ballast Specification and Testing
All the specification and types of testing that need to conduct should be referring to
the standard. In Malaysia, standards used British Standard (BS), United States
(AREMA) or Japanese Standard. The standard usage is based on client demand and
suitable for this country. In this case, ballast specification and testing by referring to
British Standard and American Standard Testing method (ASTM).
This specification part purposely to ensure the ballast materials is from good
quality when in testing after manufacturing process by the quarry. Based on BS EN
13450 (2013), which are five specifications for ballast properties to define as the
18
ballast track specification which are ballast grading, Los Angeles Abrasion (LAA),
micro-Deval attrition (MDA), flakiness index and elongation. The particle size
distribution for ballast is shown in Table 2.1.
Table 2.1: The specification for ballast particle size distributions
2.3.4 Ballast degradation and fouling
Ballast could be damaged because of the cementation with the accumulation of fines
which occur from the tamping action and other loads. This could reduce the ballast
size in certain area under sleepers and along the railway track. It also could result in
uneven support of the railway (Lam and Wang, 2011).
According to Khabbaz and Indraratna (2009), the degradation on ballast can
occurs because of the excessive dynamic loading and vibration, temperature and
moisture fluctuation and also impact load on ballast due to severe braking. Three
ways in ballast particles to degradation as following:-
(a) Small-scale asperities by grinding off (abrasion).
(b) Fracture or split of individual particles.
(c) The fragments and angular projection by breaking of that influence the initial
settlement.
Square Mesh Sieve (mm) Cumulative % by mass passing BS Sieve
6.3 100
50 70-100
40 30-65
31.5 0-25
22.4 0-3
32-50 ≥50
19
When ballast start damaged, contaminated, gradation changes and
performance reduce then this process called as fouling. The effect for the fouling
ballast depends on the types of the material, the degree it fouling and water contents
(Wee, 2004).
Drainage is one of the main purposes in railway ballasted track by providing
the large voids and storage of fouling materials. This could be happen because when
the fouling degree increases, large voids will fill in with slowly by the fouling
materials and the permeability of ballast become decrease such in Figure 2.5.
Therefore, this will create pore water pressure and the fouling materials mix with the
water (Wee, 2004).
Figure 2.5: Fouling ballast (Indraratna et al. 2014)
2.4 Particle breakage on aggregates
According to Bhanitiz (2007), particle breakage in an aggregate probably increases
when the macroscopic stress been applied, the increasing in particle size and the
reduction in number of contacts with other particles. When there has effect on the
sizes, the particle become larger and the strength will reduced.
Furthermore, the loads have been distributed through in many contact points
on the surface and then reducing the tensile stress. On the other hand, if the number
in coordination effects had dominates over the size effect, then small particles could
20
break easily. Based on conventional triaxial test, Janardhanam and Desai (1983)
concluded that the particle size of ballast significantly affect the overall resilient
modulus, volumetric and shear behaviour. It follows that track settlement is very
much dependent on the ballast quality and its response to traffic load.
There has an alternative that introduced by Indraratna et al. (2005), about the
ballast breakage index (BBI) based on particle size distribution (PSD) curves. BBI is
calculating on the basics changes in fraction passing a range of sieve as shows in
Figure 2.6. The increasing in degree of breakage could cause the PSD curve to shift
further towards the smaller particles size region on the PSD conventional plot. At
area A between the initial and final, PSD increases results in a greater BBI value. If
BBI has a lower limit of 0, means that there has no breakage happen then the limit
must be upper limit of 1. BBI can be calculated with the Equation 2.1 by referring to
the linear particle size axis. Figure 2.7shows when the ballast reaction or condition
after received some contact forces to the ballast surface.
Where,
A = area
B = the potential breakage or area between the arbitrary boundary of
maximum breakage and the final PSD.
A
BBI = (2.1)
A + B
21
Figure 2.6: Ballast breakage index (BBI) calculation method
(Indraratna et al. 2005)
Figure 2.7: Shape of ballast particle changes after the force contact
(Bhanitiz, 2007)
22
2.5 Ballast contamination
Contamination on ballast which cause by subgrade pumping and other lubricant for
example coal is one of major problem for track deterioration in many countries over
the world. Tennakoon et al. (2014) stated that any lubricant may induce load bearing
capacity or shear strength on ballast layer reducing and impede the drainage of track.
Ballast contamination could effect on the ballast layer and also transfer the pollutants
into the soil or underground water.
Ballast gravels were also constantly exposed to the other pollutants such as
acid rain because it lay on top of the rail track. Figure 2.8 and 2.9 shows the picture
of ballast contamination due to clay pumping and coal contamination. Other than
that, the contamination frequently happened due to the leaking from fuel tank, grease
dropping and heavy metals which produced from the train. It could occur from the
contact between wheel and rail or wheel and brake pad when braking (Cho et al.
2008).
Ballast also regularly exposed to weathering including the effect of freeze-
thaw, thermal effects, water, water slurries and acid rain. This could cause the ballast
particles breakdown as they are subjected to the mechanical and environmental
factors. In addition, ballast breakdown and fouling over three quarters can occur
during transportation and handling or over time due to chemical interactions (Selig
and Waters, 1994).
23
Figure 2.8: Ballast contamination due to clay pumping in Ashfield, New South
Wales, Australia (Tennakoon et al., 2014)
Figure 2.9: Ballast contamination due to coal contamination in Rockhampton,
Queensland, Australia (Tennakoon et al., 2014)
2.5.1 Acid rain effect
Ballast was constantly exposed to the other pollutants such as acid rain because it lay
on top of the rail tracks. Acid rain contamination or pollution often happens in
Southeast Asia especially in Malaysia. Nordberg et al. (1985) and Spengler et al.
24
(1990) had mentioned the contamination of toxic gasses into the main cause of acid
rain especially in urban and industrial areas.
Acid rain can be any other form precipitation that will create it become
acidic. Means that, acid rain consists of hydrogen ions but in a low pH. Based on
United States Environmental Protection Agency (2012), acid rain primarily
emissions of sulphur dioxide (SO2) and nitrogen oxides (NOx). It occurs when the
gasses reacts in the atmosphere with water, oxygen and other chemicals to form
various acidic compounds. The strongest compounds in rainwater were hydrochloric
acid (HCI), HNO, H2SOl bisulphite and ammonia (NH, HSO,).
2.5.2 Lubricant oil effect
As mentioned before, ballast could be contaminated by grease and lubricant oil due
to the wheel braking and fuel leaking from the train as in Figure 2.10. This
contamination could affect the ballast to become fouling and damage. Lubrication oil
or lube oil is the most commonly widely used because of the possible applications.
There have two basic categories of lube oil which are mineral and synthetic.
Naturally for mineral oils are refined from petroleum or crude oil. The synthetic oils
were manufactured from hydrocarbon or ester oil.
When the ballast layer was contaminated with either coal or oil, the voids
will significantly decrease the track drainage capacity due to the clogging from the
fine particles. This could cause the heaving on the pore water pressure when under
imposed load from train (Tennakoon et al. 2014).
105
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