Behaviour of ballasted track during high speed train passage

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 



Background and 

Aims 



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? 



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 



Numerical modelling of 

track-bed displacements 

Effect of train speed 



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 



2D dynamic FE mesh 

Sleeper 0.2 

Ballast 

SSB 

SB 

A 

B 

Natural ground 

0.3 

0.2 

0.2 

0.2 

0.2 


Railways Day - 15 February 2011 

Pad (0.01m thick) Rail 

V1 V2 V3 V4 

0.38 

109.2 

E1 

0.27 

E2 

E3 

31.51

Typical results: deflections 



Variation of maximum displacement 

with speed 



Field monitoring: 

methods 



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

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 



Geophone data 

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). 



a 

c 

b 

d

Comparison: PIV and geophone data 

Displacement (mm) 

0.1 

0 

-0.1 

-0.2 

-0.3 

-0.4 

-0.5 

-0.6 

6 6.5 7 7.5 8 

Time (s) 

8.5 9 9.5 10 



Geophone 

Video 

Geophones and 

PIV data are in 

agreement. 

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? 



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 



Vertical displacement vs speed 

for similar trains on HS1 



Calculate subgrade modulus from Beam on 

Elastic Foundation (BOEF) model 



Track modulus from sleeper displacements 

assuming a constant (static) axle load 



Track modulus vs displacement for all 

sleepers; track modulus assumed constant 

for an individual sleeper 



Trend lines for different speeds at 

constant modulus 



Increase in dynamic load with speed 

• Dynamic FE analysis suggest that at o.5V c (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 



Ballast issues (1) 

Ballast migration 

(ballast circles) 





Ballast migration

Ballast migration investigation: 

instrument layout 

Vertical, lateral 

and longitudinal 

sleeper velocities 

measured using 

geophones 



Measured sleeper displacements 

Vertical displacement of high rail end of sleeper is 

about 2.2 times that of low rail end 



h 

Y e 

Q e 

α 

mv /R 

2 

s 



mg 

mgsinα 

Y i 

Q i 

h c 

For a Pendolino 

traversing a curve 

of radius 1230m 

radius at 

180km/h, quasi 

static analysis 

gives Q e = 85.0 kN 

and Q i = 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 

k outer 

/k inner 

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

Dynamic analysis using Vampire gives a maximum value 

of Q e of >100kN and a load ratio of up to at least ~2.5 



Proposed mechanism 

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. 



Idealised movement of 

sleeper

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. 



Ballast issues (2) 

Ballast flight 

(flying ballast) 



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) 



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? 





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) 



Instrumentation layout 



Aerodynamic equipment installed in between sleeper 

Accelerometer position in 

ballast

Instrumentation view 



Sleeper velocity – vertical 

At the site monitored, sleeper vertical velocity was 

typically around 20mm/s 



Sleeper displacements - vertical 



Accelerations 

Filtered accelerations from ballast are similar in magnitude to 

accelerations of sleeper obtained by differentiating sleeper velocity 



Air turbulence: visual observation 



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? 



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 



Conclusions 



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 



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 



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), 113- 

128, 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 



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 





Thank you for listening

Behaviour of ballasted track during high speed train passage

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