Ballast and Sleeper Fundamentals Track21 Workshop, June 2014

Ballasted Track Enhancements:
some outcomes of the Track21 Programme
Antonis Zervos, William Powrie
Louis Le Pen, John Harkness, Taufan Abadi, Femi Ajayi,
Edgar Ferro
What is Track21
• Programme Grant funded by EPSRC
• £3.1M, 2010-2015
• Universities of Southampton (lead),
Birmingham and Nottingham
• Aim: to develop new understandings and
insights into track system and civil
engineering infrastructure behaviour
Areas covered
•
•
•
•
•
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What lies beneath
Ballast and sleepers
Track system performance
Noise and vibration
Critical zones
Economic and environmental performance
Ballast and sleepers
Objectives
1. Understand the role / requirements of ballast grading
2. Investigate “soft” techniques.

Geogrids and random fibre reinforcement
3. Investigate different sleeper types and sleeper/ballast
interface modifications such as under-sleeper pads
Ballast grading: the effect of finer material
NR: 1639kg/m3
3a: 1703kg/m3
4:
1648kg/m3
Full scale laboratory tests
Southampton Railway
Testing Facility
Load: 5 to 98.1kN
Frequency: 3Hz
Cycles ≥ 3M
Settlement vs no. of cycles: effect of ballast gradation
D50 = 27mm
D50 = 38-33mm
 Mixing in finer material, or even placing finer particles
(D50 = 16mm) on top, gives a more stable ballast layer.
 Even better: re-profiling the shoulder to 1V:2H slope
Settlement vs no. of cycles: effect of ballast gradation
1V:2H shoulder
Two-layer
 Mixing in finer material, or even placing finer particles
(D50 = 16mm) on top, gives a more stable ballast layer.
 Even better: re-profiling the shoulder to 1V:2H slope
Resilient stiffness vs no. of cycles
1V:2H shoulder
D50 = 27mm
D50 = 34mm
D50 = 38mm
Permanent settlement vs resilient stiffness
Sleeper-ballast contact analysis
Schematic graphic of Sleeper type G44, base area 2.5 m by 0.285 m
200 mm
250 mm
Pressure sensitive paper shows contact history at selected
locations below sleeper after 2.5M load cycles
Baseline
test
Increasing
finer
proportion
Visualising ballast particle movement
Start
0.25M cycles
End
Shoulder slope 1V:1H
Shoulder slope 1V:2H
Subtraction of contrast: identical photos give a black image.
Level of of gray/white shading corresponds to the magnitude of particle movement.
Fundamentals: Ballast and sleepers
Objectives
1. Understand the role / requirements of ballast grading
2. Investigate “soft” techniques.

Geogrids and random fibre reinforcement
3. Investigate different sleeper types and sleeper/ballast
interface modifications such as under-sleeper pads
Why fibre reinforcement? Seems to work in sands.
Fibre reinforced LB sand, D50 = 1.8 mm
Fibre reinforced ballast, D50 = 42 mm
Possible advantages
Understanding required
• Mechanical strength improvement
• Reduced deformation
• Influence of fibres on packing of larger
aggregates
• Could be tamped if need be
• Scaling relationships
Materials
1/5 SB
D50 ≈ 8mm
1/3 SB
D50 ≈ 14mm
Full-scale ballast
D50 ≈ 40mm
Polyethylene fibres
Effect of fibres on density
 We quantify the amount of
fibres using the
𝑉𝑓
volumetric fibre ratio, 𝑉𝑓𝑟 =
𝑉𝑠
 Fibres disrupt packing: max. and min. densities reduce with Vfr
 Even maintaining the same bulk density, the introduction of fibres (i.e.
increasing Vfr) results to a material of higher relative density.
Effect of fibres on mechanical properties
• 150 mm dia.
• 300 mm height
• Confining stress = 30 kPa
• Monotonic loading
• ~ emin (at constant relative density)
Parameters
• Vfr
• 𝐿𝑁 =
𝐿𝑓
𝐷50
• 𝑊𝑁 =
; Lf = 100mm
𝑊𝑓
𝐷50
; Wf = 35mm
Effect of fibre length for fibre content Vfr = 1.6%, 1/3rd scale ballast
Effect of fibre width for fibre content Vfr = 1.6%, 1/3rd scale ballast
• LN and WN both influence mobilised strength.
• At large strains, the influence of LN on the mobilised strength is
more prominent than WN
Scaling laws
D50 = 8mm & 14mm
D50 ~ 42mm
 Do materials with the same Vfr behave the same regardless of D50?
 Particle volume scales with (size)3
 Fibre volume for constant fibre thickness scales with (size)2
 As D50 increases, maintaining constant Vfr leads to more fibres
present for the same number of particles: different material!
 A measure other than Vfr is needed.
Scaling laws
D50 = 8mm & 14mm
D50 ~ 42mm
≈
Particle, D50
𝑁𝑓𝑝
Sphere, D50
𝑁𝑓
=
𝑁𝑝
Fibre number
Avg. no. of particles, Np
Fibres, Nf
 Materials with the same Nfp behave the same
regardless of D50
Full scale tests
LN = 7.5
WN = 2.5
Nfp = 1.33 (Vfr ≈ 0.6%)
Fibre reinforced ballast
24
The effect of fibres on settlement
Ncycles = 3 million
Fibre reinforced ballast
Unreinforced ballast
Ncycles ≈ 2 million
The effect of fibres on longitudinal pressure
Longitudinal pressure, P
Fundamentals: Ballast and sleepers
Objectives
1. Understand the role / requirements of ballast grading
2. Investigate “soft” techniques.

Geogrids and random fibre reinforcement
3. Investigate different sleeper types and sleeper/ballast
interface modifications such as under-sleeper pads
Effect of USP on long-term settlement
Technical ID
Thickness
Weight
Stiffness (CStat)
Core material
Type of USPs in the LAB tests
(made by Tiflex)
USP1 - Hard
USP2 - Soft
FC500
FC208GF
4 mm
9 mm
2
6 kg/m
5.6 kg/m2
0.228-0.311
0.079-0.105
N/mm3
N/mm3
Trackelast
Bonded cork
FC500
 Lower settlement.
 Lower rate of settlement at large numbers of cycles.
Effect of USP on sleeper-ballast contacts
Baseline test
Hard USP
Mono-block
Soft USP
Approximated Particle Size Distribution
Visual idealisation (square packing)
D90
D10
2
3
Simplified equation:
Number of contacts=
Asleeper
N. D2A
.
2
1
3
DA
3
+
2
1
+…
3
DB
3
1
3
DN
2
3
1
3
DA
:
Results evaluated as a contact efficiency:
Sleeper type
Mono- block
Test
Baseline
+ USP 1
+ USP 2
Measured
contacts
147
314
447
Potential contacts
calculated for 5 steps
513
513
513
Contact Efficiency (%)
28.0%
61.2%
87.1%
Abadi, T. C., Le Pen, L. M., Zervos, A. & Powrie, W. (Submitted Spring 2014). Measuring the Contact Area
and Pressure Between the Ballast and the Sleeper. The International Journal of Railway Technology. SaxeCoburg Publications
Next steps
www.t2f.org.uk
Track to the Future
• New programme grant, £5M plus industry /
university contributions of £3.5M
• Takes forward promising ideas from T21 and
asks some new questions
• Huddersfield as a new partner
• Increased emphasis on ground-track-vehiclepassenger interaction
Track to the Future
• Three research challenges:
• Track4Life
– New track forms and components
– Stiffness, settlement and standard deviation
– Extending ballast life and facilitating re-use
• Designer crossings and transitions
• Noise-less track
Track to the Future
• Track4Life
– New track forms and components
• to develop, and demonstrate the effectiveness of, new
track forms or components and promising
interventions identified in Track21 e.g. under-sleeper
pads and random fibre ballast reinforcement
– Stiffness, settlement and standard deviation
– Extending ballast life and facilitating re-use
Track to the Future
• Track4Life
– New track forms and components
– Stiffness, settlement and standard deviation
• to develop an understanding of the relationships
between track stiffness and track settlement, and
geometrical standard deviation, taking into account the
interactions with rail geometry and vehicle dynamics
– Extending ballast life and facilitating re-use
Track to the Future
• Track4Life
– New track forms and components
– Stiffness, settlement and standard deviation
– Extending ballast life and facilitating re-use
• to extend ballast life by reducing or eliminating the
factors leading to its degradation, assessing the
feasibility of design for the degraded state & facilitating
re-use rather than downcycling or disposal
Southampton Boldrewood
Innovation Campus
National Infrastructure Laboratory
£35M, of which £28M from UKCRIC*
*UK
40
Collaboratorium for Research in Infrastructure
and Cities
Acknowledgements
Industry Steering Group
• Network Rail
• HS2
• London Underground
• Tata Steel
• Pandrol
• Balfour Beatty Rail
• Aecom
• RSSB
• Rail Industry Association
• ATOC
• Transport Research Laboratory
University of Nottingham
• Glenn McDowell
• Jean-Francois Ferellec
• Sydney Laryea
• Mohamed Safari
EPSRC
Thank you
Any questions?