Analysis of Potential Sand Dune Impacts on Railway Tracks ...
Transcript of Analysis of Potential Sand Dune Impacts on Railway Tracks ...
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Analysis of Potential Sand Dune Impacts on
Railway Tracks and Methods of Mitigation
Duncan A. Phillips, Ph.D., P.Eng.
Senior Consultant / Principal
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Acknowledgements
• The information presented here is based
on the work of many bright and committed
people.
• They teach me things every day.
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Outline
• Statement of Problem
• Available Information for GCC
– Sand properties
– Meteorology
• Options Available
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Problem Statement
Sand and railways don’t mix…
Specific challenges / problems include:
• Track blockages
• Ballast ingress / contamination
• Fouling of electrical systems
• Jamming of switch / gear boxes
• etc.
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Problem Statement
The consequences of sand on tracks
include:
• Increased track maintenance – cleaning
• Changes in track bed damping
• Reduced traffic speeds
• Schedule delays
• Safety concerns
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Problem Statement
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Images reproduced from: Zhang, K.C., J.J. Qu, K.T Liao, Q.H. Niu, and Q.J Han (2010), Damage by wind-blown sand and its control along Qinghai-Tibet Railway in China, Aeolian Research 1 (2010) 143–146.
These challenges exist anywhere that deserts and
infrastructure meet. Examples from China:
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Options to Reduce Impact of Sand on Operations
1) Adjust route to avoid moving sand
– Be aware of risks before planning route
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Options to Reduce Impact of Sand on Operations
2) Reduce quantity of sand landing on tracks
– Plan the upwind slopes properly
• Profiles
• Materials
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Options to Reduce Impact of Sand on Operations
3) Make is easier for sand to leave tracks
– Make track aerodynamically smooth
• This will require some design work
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Options to Reduce Impact of Sand on Operations
4) Reduce the severity of the presence of
sand
– Choose sand resistant track beds
• Slab track in the worst regions?
• Elevated?
• Covered ballast?
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Other Locations Deal with Particle Problems – Elevating Structures
Photo by BAS
View Direction
Can be jacked up
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Halley V South Pole Research Station
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Some Strategies Need Maintenance
Existing
Proposed
Time instance 1 Time instance 2
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The physics of wind blown sand
Wind Speed Threshold
• minimum wind speed needed to start sand grains saltating (m•s-1).
Saltation
• movement of sand in successive hops across a surface (hop lengths & trajectories dependent on various surface, sand, and wind characteristics)
Sand Flux
• Bulk sand transport rate / amount of sand in motion (kg•m-1•yr-1)
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The physics of wind blown sand
How are these determined?
• Field measurements
– site-specific biases and complications,
difficult to reproduce results, expensive
• Portable / open-floor wind tunnels
– Limited access to equipment, site-
specific biases / complications,
expensive
• Laboratory wind tunnels
– Highly controlled environment,
reproducible, limited sample sizes
cause biases
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© G. Wiggs
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Characteristics of aeolian sands
HafeetD = 0.161 mm
KhatimD = 0.153 mm
LahbabD = 0.176 mm
RAK SouthD = 0.179 mm
TaweelahD = 0.173 mm
0 5
mmApprox. scale:
Aeolian (wind-blown) sand is similar the world over. Different colours are typically a result of environmental conditions (e.g., reddish grains suggest iron staining) that do not affect wind speed threshold or flux rates. Examples from UAE shown below.
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AUH
DBX
SHJ
RKT
AAN
Meteorology Differs Across the Region
Win
d S
pe
ed
(m
/s)
Meteorological conditions vary widely over large geographic
areas yet it is rare to find robust meteorological data at high
spatial resolution and of a sufficiently long period of record,
especially in remote, desert environments.
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This can be used to
generate site-specific
climate models.
Meteorology
Cannot rely on unrepresentative airport observations.
Using computer simulations it is possible to generate gridded meteorological fields over large areas at relatively high spatial and temporal resolutions.
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Meteorology
200–400 VU ~ 17–33 m3•m-1•yr-1
This method has been used
to generate crude maps of
sand drift potential over
large desert regions but not
specifically for local areas
or infrastructure projects.
For example, Fryberger et
al. (2006) report average
drift values of 18 m3•m-1•yr-1
in northeastern Saudi
Arabia, with a maximum of
29 m3•m-1•yr-1 in high wind
areas.
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Meteorology & Sand Drift Risk
Abu Dhabi
Liwa
Dubai
Al Ain
Example: Annual hours above threshold (example year).
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Meteorology & Sand Drift Risk
The data permits us to analyse the issues in new ways and greater
detail…
In Egypt, the values exceed 40 m height: this is sand dune.
Example: Annual flux potential in kg•m-1•yr-1 (example year).
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0 m
10 m
5 m
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Sand Drift Risk
Typical Sand Transport StatisticsLocation SEG-A
FREQUENCY (HOURS/YR) 1152
MAGNITUDE OF SAND FLUX (1000KG/M/YR)
9.3
NET SAND DRIFT (1000KG/M/YR) 3.2
NET DRIFT RATIO 34.4%
DRIFT VECTOR 289
# SIGNIFICANT BLOWING SAND EVENTS PER YEAR
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Frequency (hrs•yr-1)
• Total hours per year above threshold.
Magnitude Sand Flux (kg•m-1•yr-1)
• Total amount of sand (kg) that moving per
unit width (m) in a given year.
Net Sand Drift (kg•m-1•yr-1)
• Amount of sand (kg) contributing to the net
dune migration / vector.
Net Drift Ratio
• Percent of total sand transport that
contributes to the net drift vector.
Drift Vector
• Compass direction of drift (dune migration).
No. Significant Blowing Sand Events per Year
• Number of times a year when wind is above
threshold for three or more consecutive
hours
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Mitigation Options
• Many options have been tried– Environmental issues with surface coating with oil
– Porous fencing is expensive to maintain / replace
– Ballast cleaning is expensive and affects schedules
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Zhang, K.C., J.J. Qu, K.T Liao, Q.H. Niu, and Q.J Han
(2010), Damage by wind-blown sand and its control
along Qinghai-Tibet Railway in China, Aeolian
Research 1 (2010) 143–146.
Dong, Z., G. Chen, X. He, Z. Han,and X. Wang
(2004), Controlling blown sand along the
highway crossing the Taklimakan Desert,
Journal of Arid Environments, 57, (2004), 329–344.
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Mitigation Strategies
• Mitigation must work with Mother Nature
and the natural equilibrium between wind
and sand.
• Strive for multiple layers of protection
– Eliminate sand sources
– Design for smaller likelihood of deposition
– Encourage re-entrainment of sand at track
– Reduced impact if sand does deposit
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An optimal cross-section should encourage
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Wind-porous track profiles can help reduce build up of sand
Deposition of sand upwind / away from the rail embankment
Higher wind speeds over the track embankment and rails: accelerate wind
… reduce the “carrying capacity” of the wind …
… accelerate the wind flow …
Create an aerodynamically smooth surface
Ballast stone is a problem; not a solution….
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Mitigation
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WIND
42 31
c
road
Not to Scale - for illustrative purposes ONLY
Theoretical Mitigation Option
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Closing / Synopsis
• Drifting and blowing sand is a significant challenge to the GCC rail network.
• The success rate of mitigation options is mixed; none are fool proof.
• Mitigation must work with Mother Nature and the natural equilibrium between wind and sand.
• New tools exist that allow us to look at these issues in more holistic ways.
• There are some track topologies that need testing.
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