Behaviour of ballasted
track during high speed
train passage
William Powrie and Jeffrey Priest
University of Southampton
High Speed Track
Railways Day - 15 February 2011
Outline of talk
• Background and Aims
• Sub-base issues: effect of train speed on
vertical track movements during train
passage
- numerical analysis
- field monitoring
• Ballast issues
- ballast migration
- flying ballast
• Conclusions
High Speed Track
Railways Day - 15 February 2011
Background and
Aims
High Speed Track
Railways Day - 15 February 2011
Background
• Increased train speeds on both new and classic railway
lines
• Lack of detailed analytical understanding of track system
/ sub-soil behaviour, even for traditional speed railways
• Not sure how well past experience and observation
(empiricism) will extrapolate to higher speed lines
• Application of recent advances in soil mechanics and
instrumentation ⇒ improved understanding of ballast
and sub-base performance ⇒ better whole life cost
modelling
• Is ballasted track the best choice for high speed rail?
High Speed Track
Railways Day - 15 February 2011
Aims
• To assess the effects of train speed on the
load/deformation response of the track
foundation, by analysis and field
measurements
• To investigate some additional problems
associated with the use of ballasted track
for high speed railway lines
High Speed Track
Railways Day - 15 February 2011
Numerical modelling of
track-bed displacements
Effect of train speed
High Speed Track
Railways Day - 15 February 2011
Method
• Dynamic, 2D finite element analysis using
ABAQUS
• Elastic, undrained response
• Interpretation in terms of total stresses
• Loading magnitude and geometry based on
Spoornet COALlink line (“Cape” gauge, 1067 mm)
• 130 kN maximum wheel load
• Analysis modelled the vertical centre plane along
the track, and passage of a three-wagon train
• Model validated with reference to field data
High Speed Track
Railways Day - 15 February 2011
2D dynamic FE mesh
Pad (0.01m thick)
Rail
0.38
Sleeper
0.27
0.2
V1
Ballast
0.3
SSB
0.2
V2
V3
V4
E1
0.2
A
0.2
B
0.2
E2
31.51
SB
E3
Natural ground
109.2
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Railways Day - 15 February 2011
Typical results: deflections
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Railways Day - 15 February 2011
Variation of maximum displacement
with speed
High Speed Track
Railways Day - 15 February 2011
Field monitoring:
methods
High Speed Track
Railways Day - 15 February 2011
Measurement techniques: remote
video monitoring
Webcam captures digital video images
of a target, from which displacement is
calculated using computer algorithm.
Digital camera frame rate up to 170fps
High Speed Track
Railways Day - 15 February 2011
Measurement techniques: geophones
Geophones: LF24, 1 Hz natural frequency, logged at 500Hz
Mounted on sleeper or positioned in borehole at different
depths in the ground
High Speed Track
Railways Day - 15 February 2011
Geophone data
a
b
c
d
Geophone produces a voltage proportional to velocity of the sensor (a). Knowing the response
characteristics of the geophone the velocity can be computed (b). Integration of data leads to calculated
displacement (c). Dominant axle and bogie frequencies can be obtained (d).
High Speed Track
Railways Day - 15 February 2011
Comparison: PIV and geophone data
Geophones and
PIV data are in
agreement.
0.1
Geophone
Video
0
Displacement (mm)
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
6
6.5
7
7.5
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Railways Day - 15 February 2011
8
Time (s)
8.5
9
9.5
10
Video frame rate
of 30fps gives an
image every
880mm of travel
compared with
53mm for 500 Hz
geophones. Both
methods capture
displacements due
to individual axles.
Field monitoring:
results
What happens in reality?
High Speed Track
Railways Day - 15 February 2011
Effect of train speed: HS1
• Standard gauge (1435 mm)
• Same trains (Class 390 Eurostar sets)
• Static axle load 15.36 tonne (wheel load ~ 75.3 kN)
• Speeds ~ 120 km/hr and 270 km/hr
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Railways Day - 15 February 2011
Vertical displacement vs speed
for similar trains on HS1
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Railways Day - 15 February 2011
Calculate subgrade modulus from Beam on
Elastic Foundation (BOEF) model
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Railways Day - 15 February 2011
Track modulus from sleeper displacements
assuming a constant (static) axle load
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Railways Day - 15 February 2011
Track modulus vs displacement for all
sleepers; track modulus assumed constant
for an individual sleeper
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Railways Day - 15 February 2011
Trend lines for different speeds at
constant modulus
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Railways Day - 15 February 2011
Increase in dynamic load with speed
• Dynamic FE analysis suggest that at o.5Vc (train
speed = 400km/h) dynamic load increases by less
than 10% of static, so at 260km/h dynamic load ≈
static load
• Field monitoring suggests dynamic load at
260km/h is around 1.2 – 1.3 × static
• At 260km/h, Li and Selig (1998) suggest dynamic
load increases to around 2.45 × static
High Speed Track
Railways Day - 15 February 2011
Ballast issues (1)
Ballast migration
(ballast circles)
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Railways Day - 15 February 2011
Ballast migration
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Railways Day - 15 February 2011
Ballast migration investigation:
instrument layout
Vertical, lateral
and longitudinal
sleeper velocities
measured using
geophones
High Speed Track
Railways Day - 15 February 2011
Measured sleeper displacements
Vertical displacement of high rail end of sleeper is
about 2.2 times that of low rail end
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Railways Day - 15 February 2011
2
mv /R
mgsinα
mg
Ye
α
h
Qe
hc
Yi
s
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Railways Day - 15 February 2011
Qi
For a Pendolino
traversing a curve of radius 1230m radius at 180km/h, quasi static analysis gives Qe = 85.0 kN
and Qi = 49.2 kN, i.e. a ratio of loads of 1.73 Train Run
Inner rail
δ mm
Outer rail
δ mm
Ratio
δinner /δouter
Ratio
kouter
/kinner
1
0.390
0.853
2.19
1.27
2
0.414
0.900
2.17
1.25
3
0.402
0.903
2.25
1.30
4
0.387
0.908
2.35
1.36
Ratio of deflections is greater than the ratio of quasi‐
static loads implying difference in support stiffnesses
High Speed Track
Railways Day - 15 February 2011
Dynamic analysis using Vampire gives a maximum value
of Qe of >100kN and a load ratio of up to at least ~2.5
High Speed Track
Railways Day - 15 February 2011
Proposed mechanism
Idealised movement of
sleeper
During loading sleeper rotates about the low rail end and
moves towards the high rail end. Due to shape of sleeper
ballast falls vertically during loading and is pushed up (down
slope) during unloading.
High Speed Track
Railways Day - 15 February 2011
WCML: vertical movements due to
loco + coaches vs Pendolino trainset
Class 87 locomotive produces displacements comparable with the Class
390 Pendolino train; displacements for Mk3 coaches are considerably less.
High Speed Track
Railways Day - 15 February 2011
Ballast issues (2)
Ballast flight
(flying ballast)
High Speed Track
Railways Day - 15 February 2011
Flying ballast
• Geotechnical and aerodynamic investigation
in collaboration with University of
Birmingham (aerodynamics: Professor Chris
Baker, Dr Andrew Quinn) and Network Rail
HS1 (David Hutchinson, Mick Hayward)
High Speed Track
Railways Day - 15 February 2011
Background
• During passage of a high speed train, ballast
particles become detached from the ballast bed
(“flying ballast”)
• Cause rail defects which require grinding to
repair
• Causes damage to undercarriages and exposed
equipment unless protection is provided
• At present the cause is not understood
• Is it mechanical, aerodynamic or a
combination?
High Speed Track
Railways Day - 15 February 2011
High Speed Track
Railways Day - 15 February 2011
Measurements
• Geophones to measure velocities of
sleepers during train passage
• Accelerometers to measure accelerations
of the ballast
• High speed camera to observe air
turbulence near sleeper (Professor Chris
Baker, University of Birmingham)
High Speed Track
Railways Day - 15 February 2011
Instrumentation layout
Aerodynamic equipment installed in between sleeper
Accelerometer position in
ballast
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Railways Day - 15 February 2011
Instrumentation view
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Railways Day - 15 February 2011
Sleeper velocity – vertical
At the site monitored, sleeper vertical velocity was
typically around 20mm/s
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Railways Day - 15 February 2011
Sleeper displacements - vertical
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Railways Day - 15 February 2011
Accelerations
Filtered accelerations from ballast are similar in magnitude to
accelerations of sleeper obtained by differentiating sleeper velocity
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Railways Day - 15 February 2011
Air turbulence: visual observation
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Railways Day - 15 February 2011
Does the track see this turbulence?
Slight increase in voltage is observed just before train arrives
(4.2 m ahead of first wheel). Is this caused by the turbulence?
High Speed Track
Railways Day - 15 February 2011
Ballast flight: findings
• Sleeper velocity was reasonably consistent for all train
passages and sleepers ~ 20 mm/s
• Maximum ballast accelerations were ~ 3 m/s
• Geotechnical effects (ground accelerations) alone are
insufficient to cause ballast flight: the cause is probably a
combination of aerodynamic and ballast acceleration effects
• Video recording showed pulse of air, which is quite
turbulent, travelling in front of train, which may give rise to
downward force into ballast
High Speed Track
Railways Day - 15 February 2011
Conclusions
High Speed Track
Railways Day - 15 February 2011
Conclusions
• Stresses and deflections increase with train speed perhaps more than analysis of “perfect” track would
suggest, but less than current empirical rules allow
• Differential forces on rails when curving at high cant
deficiency together with sleeper geometry and
trainset operation (⇒ 10 × the number of high load
events per train pass) can cause ballast migration
• Combined aerodynamic and ground vibrational
effects can lead to ballast flight
High Speed Track
Railways Day - 15 February 2011
Journal papers (1)
• Monitoring the dynamic displacements of railway track. D Bowness, W
Powrie, A C Lock, J A Priest and D J Richards. Proc I Mech E Part F, J
Rail and Rapid Transit 221 (F1), 13-22, March 2007. Awarded IMechE
John F Alcock Memorial Prize and Thomas Hawksley Gold Medal
• Stress changes in the ground below ballasted railway track during train
passage. W Powrie, L A Yang and C R I Clayton. Proc I Mech E, Part F, J
Rail and Rapid Transit 221 (F2), 247-261, May 2007
• Dynamic stress analysis of a ballasted railway track bed during train
passage. L Yang. W Powrie and J A Priest. J ASCE Geotechnical and
Geoenvironmental Engineering 135(5), 680-689, May 2009
• Determination of dynamic track modulus from measurement of track
velocity during train passage. J A Priest and W Powrie. J ASCE
Geotechnical and Geoenvironmental Engineering 135(11), 1732-1740,
November 2009
High Speed Track
Railways Day - 15 February 2011
Journal papers (2)
• A full-scale experimental and modelling study of ballast flight under
high-speed trains. A D Quinn, M Hayward, C J Baker, F Schmid, J A
Priest and W Powrie. Proc I Mech E, Part F, J Rail and Rapid Transit
224 (F2), 61-74, 2010
• Measurements of transient ground movements below a ballasted railway
line. J A Priest, W Powrie, L Yang, P J Gräbe and C R I Clayton.
Géotechnique 60(9), 667-677, September 2010
• Contribution of base, crib, and shoulder ballast to the lateral sliding
resistance of railway track: a geotechnical perspective. L M Le Pen and W
Powrie. Proc I Mech E, Part F, J Rail and Rapid Transit 225(F2), 113128, 2011
• An assessment of transition zone performance. B Coelho, P Hölscher, J A
Priest, W Powrie and F Barends. Proc I Mech E, Part F, J Rail and Rapid
Transit 225(F2), 129-139, 2011
High Speed Track
Railways Day - 15 February 2011
Acknowledgements
• EPSRC
• Daren Bowness, Chris Clayton, Tony Lock, Louis le
Pen, David Richards, Liang Yang; University of
Southampton
• David Hutchinson, Mick Hayward; Network Rail CTRL
• Chris Baker, Andrew Quinn; University of Birmingham
• Patric Mak, Mark Burstow, James Dean; Network Rail
High Speed Track
Railways Day - 15 February 2011
Thank you for listening
High Speed Track
Railways Day - 15 February 2011