Track 21
• 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
15 key findings and outputs
Areas covered
• What lies beneath
• Ballast and sleepers
• Track system performance
• Noise and vibration
• Critical zones
• Economic and environmental
performance modelling
1. Behavioural mechanisms have been
identified for discrete piles used to
stabilise embankment and cutting slopes,
that have led to more economic design
and construction
Discrete pile stabilization of
infrastructure slopes
Strain gauges
and
inclinometer
tubes in piles
Inclinometer
tubes in
between piles
Also:
• Inclinometer
tubes at toe and
crest of slope
• Piezometers
• Raingauge
Discrete pile stabilization: monitoring
Discrete piles: mechanisms
(a) Hildenborough
(b) Mill Hill, short term
Displacement
(c) Mill Hill, long term and Grange Hill
Pressure
Displacement
Pressure
Major driving
pressure is inward
shrinkage of
embankment
Pressure on the
top of the pile is
downslope
Estimated financial benefits (from REF2014
impact case study on rail infrastructure): slope
stabilization
• £900k in cost (50%), 2 months (33%) in time,
emergency remedial works at Acton Town,
winter 2011
• £1.5M in cost (40%), 4 months (50%) in time
at Cannons Park, January 2012 (Olympicscritical)
• Estimated savings £65M to £100M over a 5year period
2. Seasonal shrink/swell is minimised if
high water demand trees are more than
the tree height away from the tracks
3. Leaving the trees in place at the toe of
an embankment retains winter suctions
Ballast
Grass
Trees
(b)
(a)
(c)
End of winter (February 2001) pore water pressure contours (a) For a slope with
trees at the toe only (b) for a grass covered slope and (c) for a tree covered slope
Benefits (from REF2014 impact case study on
rail infrastructure): vegetation and slope stability
• Influenced NR vegetation management guidance
and strategy, with estimated national savings of
£1M over the preceding two years from reduced
costs and delays
• Influenced LUL vegetation management guidance
and strategy
• Improved risk assessment of earthworks in NR
adverse weather management strategy, reducing
risk of trains running into landslides during
periods of high rainfall by 14%
Principal stress rotation
As a train
approaches,
recedes,
accelerates or
brakes a soil
element in the
sub-base layer of
a railway track
experiences a
rotation in
principal stresses.
Fig. 1.1 (a) Principal stress rotation redrawn from Brown (1996)
Hollow cylinder sample
with local
instrumentation
4. Increasing the clay content reduces the
susceptibility of the subsoil to failure in
principal stress
rotation
5. Principal stress rotation can reduce
sub-base resilient modulus by 20% of its
value under pure axial load. An increase
in water content (loss of suction) can
reduce it by almost 90%.
6.
Response of old
embankments
to axle load is
highly nonlinear
(add-on work with
Mott MacDonald,
funded by RSSB)
7. Under-sleeper pads increase the number
of particle contacts, reduce contact
stresses and reduce long-term settlement
USPs tested: results with monoblock
Technical ID
Thickness
Weight
Stiffness (CStat)
Core material
Type of USPs in the LAB tests
(made by Tiflex)
USPA - Hard
USPB - 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
Sleeper/ballast interface with USPs under Mono-block
Baseline test
Mono-block
Hard USP
Soft USP
8. Altering the ballast grading curve by the
addition of finer particles reduces particle
contact stresses and long term settlements
Increasing proportion of
finer material
9. Random fibre
reinforcement
increases ballast
ductility...
…and reduces long term settlements
10. Reducing the shoulder slope, or
constraining the ballast from lateral
movement, has the greatest effect on
reducing long-term settlements
Reducing the shoulder slope
Reducing the shoulder slope
Ballast particle movements
(a) start, (b) 0.25 million cycles (c) end
twin-block sleeper test
Shoulder slope 1V:1H
RPS slope test
Shoulder slope 1V:2H
Subtraction of contrast: identical gives a black image. Where particles have
moved about, the subtraction is not zero and shows as a shade of grey/white
11. Ballast disturbance features are caused
by excessive movements, arising from soft
features, sudden changes in support, or
abnormal loads
Migration (dynamic loads or soft support)
Soft support (wetbed)
Bridge expansion joints (dynamic loads, varied support)
Ballast migration reproduced in discrete
element analysis using potential particles
12. Measurement train data can be
correlated …
… with deflections measured
at the trackside
13. Ballast
fouling by
sand
increases
stiffness
and
reduces
long term
settlement
14. Track renewal can increase noise
•
•
•
•
•
Case study: track renewal at Fishbourne.
New track was slightly smoother (~1 dB)
Old track: stiff pads; new track: soft pads
Modern EMU – relatively small wheels.
Noise increased by 3-4 dB. Correctly predicted by the TWINS
model.
Controlling track noise
• Treating the track alone can give significant noise reductions
of 4–5 dB.
• Rail dampers: much less intrusive than noise barriers (and
cheaper).
15. Varying the ballast gradation has more
potential for controlling noise than varying
the ballast stiffness
Life cycle cost modelling
Issues
• Limited knowledge of the financial benefits
of improved track maintenance and renewal
measures
• Wider benefits of improved track
maintenance and renewal measures largely
unknown
TRACK21 research - ongoing
• Quantification of cost implications of track
system interventions
– Direct impacts on maintenance and renewal
costs
– Noise and vibration levels
– Passenger comfort
– Maintenance-associated train delays
– Rolling stock damage
TRACK21 research - ongoing
• Whole-life carbon modelling of track system
interventions
– Impacts of changes in renewal and maintenance
activities
– Embedded carbon in track materials
– Wider emission impacts
• 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
Thank you