KRRIRRUKSR2 Rail Technology Seminar

1
KRRI/RRUK/SR2 Rail Technology Seminar

• Institution of Mechanical Engineers, London
• 27 September 2006
• Infrastructure
• William Powrie University of Southampton

2
OUTLINE

• Overview of the asset base
• Challenges
• Rails
• Track foundations
• Earthworks (embankments and cuttings)
• Bridges
• Concluding remarks

3
THE ASSET BASE

• 16 652 route km
• 33 796 track km
• 3 000 embankments
• 3 000 cuttings
• 40 000 bridges
• (Source http//www.railway-technical.com/statisti
  cs.html)

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Challenges 1 DESIGN LIFE

• Design life for infrastructure (albeit this is a
  modern concept) is commonly 120 years
• We cannot afford to replace the asset base on a
  120-year cycle
• ? WE MUST FIND WAYS OF EXTENDING THE LIFE OF THE
  ASSET BASE

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Challenges 2 INCREASED LOADS

• Higher speeds (225 km/h) increasingly becoming
  standard CTRL genuinely high speed (300 km/h)
• Pendolino trains enable higher speeds on old
  track geometry ? higher cornering loads
• More trains/ more congested network
• Replacement of 1st generation locos coaches by
  2nd generation dmus led to reductions in axle
  loads, now being reversed by crashworthiness
  requirements of 3rd generation dmus
• Climate change effects

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Challenges 3 MAINTENANCE

• Increased loads and ageing asset base (previous
  slides) require more maintenance
• Expectation of 24/7 railway operation (less time
  for maintenance)
• Population/demographics/social changes mean fewer
  workers prepared/able to do heavy manual
  maintenance
• ? WE MUST FIND WAYS OF AUTOMATING/ REDUCING
  MAINTENANCE NEEDS

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MEETING THE CHALLENGE

• Better scientific understanding of underlying
  mechanisms of material and structure behaviour
• Experiments
• Modelling
• Observation
• Analysis
• Improved design
• Decisions based on whole life costs

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MEETING THE CHALLENGE

• Rails (Newcastle, Birmingham)
• Track (Southampton, Birmingham)
• Earthworks (Southampton)
• Bridges (Southampton)

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RAILS BACKGROUND

• Rail grinding practised by BR to eliminate
  corrugations
• Practice discontinued as corrugations disappeared
  
• Use of hardened mill heat treated (MHT) rail
  slowed rate of natural wear
• With hardened rails, crack growth is faster than
  wear
• Cracks join up ? Hatfield (rolling contact
  fatigue)
• Need to understand relative rates of wear and
  crack growth in selection and planning
  maintenance of rail steels

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RAIL STEEL STUDIES AT NEWCASTLE and BIRMINGHAM
(Ajay Kapoor and Claire Davis)

• Modelling and metallurgical studies to
  investigate relative rates of crack growth and
  wear in different types of rail steel
• ? Optimisation of steel type for different
  service loading and conditions

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RAIL STEEL STUDIES Analysis of rail
microstructure

• Chemical, optical, electron microscope
  examination of worn and cracked rail and twin
  disc test samples to examine crack initiation
  mechanisms.
• Nano-hardness testing of the individual strained
  phases near-surface to determine straining
  response.
• Observation of short cracks initiating along the
  ferrite bands

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RAIL STEEL STUDIES Testing and Simulations

• Analyses and simulations show that cracks form in
  the sheared ferrite bands
• Hence rail life will be longer for steels with a
  higher proportion of pearlite

Improved random microstructure.
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TRACK FOUNDATIONS BACKGROUND
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TRACK FOUNDATIONS BACKGROUND

• Traditional maintenance by tamping to maintain
  line and level
• We proof the ballast against vertical loads by
  loading it horizontally!
• Ballast memory effects
• Tamping does not seem to cure voids below
  sleepers ? stoneblowing (placing small stones
  into voids below sleepers)
• Influence of sub-soil

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MEASUREMENT OF TRACK DEFECTS

• New Measurement Train recording carried out at
  225 km/h but we measure the deflected position of
  the track and rails
• Cannot establish an absolute datum on the move
• Therefore do not know about deflections under
  load, i.e. track and sub-base stiffness
• ? NEED TO DEVELOP WAYS OF MEASURING TRACK
  DEFLECTIONS DURING TRAIN PASSAGE

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Measurement techniques
Remote video monitoring

• Webcam captures digital video images of a
  target from which displacement is calculated
  using computer algorithm.
• Current webcam records at 30fps

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Measurement techniques
Geophones
Front view of access pit
Cross section through track structure
Track structure (ballast, sleeper, rail)
A
A
200
Access pit A
B
B
800
3 m
C
C
200
C
D
D
D
1 m
Approx. 6 m
Geophones- LF 24 1 Hz natural frequency Logged
at 500Hz Mounted on sleeper or positioned in
borehole at differing depths in formation
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Channel Tunnel Rail Link
To monitor dynamic displacement during
tunnelling under line 8 targets (and geophones)
attached to sleepers Measurements taken before,
during and after tunnelling Monitoring in
addition to static measurements All trains
captured were full Class 373/1 Eurostar sets with
the trailers having a near uniform axle loading
of approximately 15 tonnes.
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CTRL cont-
Typical displacement response for CTRL
track. Lower plot shows variation in sleeper
displacement for section of CTRL. Sleeper No 4
shows highest deflection and may be hanging.
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CTRL cont-
Comparison between geophone and PIV show that
both are in agreement. Using a frame rate of
30fps for the video monitoring equated to an
image being acquired for every 880mm of travel
compared to 53mm for the geophones (500Hz). Given
these limitations both methods easily capture the
displacements due to individual axles.
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Loughborough
Investigation of embankment on Great Central
Railway line near East Lake, Loughborough.
Single line heritage track carrying gypsum to
nearby factory Class 60 Loco pulling 18 wagons.
Line limited to 10mph 0.2Hz Joint monitoring
with BGS and University of Birmingham
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Loughborough cont-
Nearly 6mm of deflection was recorded for Class
60 Loco pulling 18 empty wagons. For the loaded
train the deflections were so large the target
moved out of the field of view of the webcam
during the train passage. Manual estimates showed
maximum deflections for wagons around 7.7mm.
Sensitivity of geophone and filtering process
underestimates deflections at low speeds
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Track/ballast interface stability
Aim to investigate the lateral stability of the
track/ballast interface under loads applied by

• Tilting trains cornering at high speed
  Side-winds
• Dynamic effects (hunting) Thermal effects in CWR

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Track/ballast interface stability

• Test rig
• Measurement of lateral resistance from base,
  shoulder and crib ballast
• Geophone measurements
• Measuring dynamic sleeper movements on a curve of
  the West Coast Main Line (WCML)
• Modelling
• Results from laboratory / field tests will be
  used to development conceptual and numerical
  models

Sleepers rig under construction
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EARTHWORKS

• Pile stabilisation of embankment slopes
• Effects of vegetation and climate change

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Stabilisation of earthworks slopes using discrete
piles
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Hildenborough
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Hildenborough
Piles contain inclinometer tubes and 6 pairs of
strain gauges
Inclinometer tubes midway between piles
A
B
C
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Hildenborough slope displacements
Day 42 after pile construction (10 May 2001)
shortly after rockfill regrading
Day 1345 after pile construction (01 Dec 2004)
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Hildenborough pile displacements
Day 42 after pile construction (10 May 2001)
shortly after rockfill regrading
Day 1345 after pile construction (01 Dec 2004)
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Hildenborough pile slope displacements
Rockfill
Day 42
EFC
Difference between pile and soil displacements
Day 1345
Weather-ed and intact WC
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Mill Hill
Discrete pile stabilised Anglian Till embankment,
13 m high
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Grange Hill
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Vegetation effects

• London Clay cut slope on the A34 near Newbury,
  7.5m high, 16 slope

Instrumented section of slope
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Newbury site - background

• London Clay cut slope, 7.5m high, 16 slope

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Flushable piezometers, tensiometers (both measure
suction to 90 kPa), Equitensiometer to measure
suction to 1500 kPa
Datalogger and weather station, including
measurements of rainfall and the parameters
required to calculate evapotranspiration
Instrumentation of a London Clay cut slope at
Newbury
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Newbury measured change in pore water pressures
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Newbury envelope of pore water pressure changes
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Calculated and measured SMD
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Effect of climate change on soil moisture deficit
BETWIXT climate data set for Heathrow (daily
BETWIXT data derived from Hadley 02 climate
model) For London Clay assuming rough grass cover
with grass rooting to 1.2m depth Water in profile
readily available to plants 80mm, total
available water 200mm
Measured data
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Bridges and struts

• Many are old, of uncertain design / materials
• e.g. wrought iron masonry
• Some need to be replaced others can be repaired
  / strengthened to prolong service life
• e.g. carbon fibre composites (CFC) reinforcement
  of iron struts (Shadwell) and bridges

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Struts Shadwell Station
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Wrought Iron (WI) bridges strengthening with
CFC (background)

• WI produced by repeated beating and rolling
  whilst heated close to melting ? laminar
  structure
• Six rollings produced the best quality WI
• Slag fibres aligned in the direction of rolling ?
  with-grain and cross-grain properties are very
  different
• With-grain there is good ductility (elongation to
  failure gt 12) but cross-grain it is brittle
  (elongation about 2.5)
• Concern that strengthening using carbon fibre
  composite would cause delamination of WI.

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Wrought Iron bridges strengthening with cfc
(findings)

• Strength is greater in compression but stiffness
  is about the same. At yield in compression,
  specimens delaminate.
• Considerable variability, between specimens from
  one source and between sources from different
  locations.
• CFRP strengthening is possible but care must be
  taken with the position of the neutral axis of
  the strengthened section
• If neutral axis is too close to the tension
  flange, compressive stresses will increase which
  could lead to delamination

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CONCLUDING COMMENTS Infrastructure Needs

• Prolong design / service life of infrastructure
• not affordable to replace on 120 year cycle
• Reduce maintenance requirements
• 24/7 railway ageing population
• Assess / repair / modify for increasing loads
• More / faster trains climate change effects

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CONCLUDING COMMENTS the way forward

• Increased understanding of underlying mechanisms
  of material and overall behaviour, through
  theory, experiment, observation and analysis
• Use this understanding to understand whole life
  costs (capital vs recurrent/maintenance
  expenditure)
• Plan and design infrastructure accordingly, with
  emphasis on whole life costs

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KRRI/RRUK/SR2 Rail Technology Seminar

• THANK YOU FOR YOUR ATTENTION
• William Powrie University of Southampton

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INFLUENCE OF SUB-SOIL
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Finite element analysis
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Stress distribution
Vertical stress contour at centre plane
(compressive stress as negative)
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Calculated principal stress rotations
(a)
(b)
PSR under different initial stress states (a) K0
0.5 (b) K0 2.0
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Hollow cylinder apparatus
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Principal stress rotation (PSR)
Cyclic triaxial test
Cyclic hollow cylinder test
Courtesy of Dr Hannes Grabe
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Axial Strains with and without PSR
Courtesy of Dr Hannes Grabe