analysis of potential sand dune impacts on railway tracks

Reputation Resources Results

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www.rwdiair.com

Analysis of Potential Sand Dune Impacts on

Railway Tracks and Methods of Mitigation

Duncan A. Phillips, Ph.D., P.Eng.

Senior Consultant / Principal

[email protected]


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:


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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2) Reduce quantity of sand landing on tracks

– Plan the upwind slopes properly

• Profiles

• Materials

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3) Make is easier for sand to leave tracks

– Make track aerodynamically smooth

• This will require some design work

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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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Reputation Resources Results 11

Remove sand manually


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


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


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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Computer Meteorology Models can Provide Annual Information

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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


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.


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


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….


Mitigation

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WIND

42 31

c

road

Not to Scale - for illustrative purposes ONLY

Theoretical Mitigation Option


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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THANK YOU FOR YOUR KIND

ATTENTION

[email protected]

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analysis of potential sand dune impacts on railway tracks

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