Analysis of Potential Sand Dune Impacts on Railway Tracks and Methods of Mitigation

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1 Analysis of Potential Sand Dune Impacts on Railway Tracks and Methods of Mitigation Duncan A. Phillips, Ph.D., P.Eng. Senior Consultant / Principal Duncan.Phillips@rwdi.com Canada USA UK UAE India China wdiair.com

2 Acknowledgements The information presented here is based on the work of many bright and committed people. They teach me things every day. 2

3 Outline Statement of Problem Available Information for GCC Sand properties Meteorology Options Available 3

4 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. 4

5 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 5

6 Problem Statement These challenges exist anywhere that deserts and infrastructure meet. Examples from China: 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)

7 Options to Reduce Impact of Sand on Operations 1) Adjust route to avoid moving sand Be aware of risks before planning route 7

8 Options to Reduce Impact of Sand on Operations 2) Reduce quantity of sand landing on tracks Plan the upwind slopes properly Profiles Materials 8

9 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 9

10 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? 10

11 Remove sand manually 11

12 Other Locations Deal with Particle Problems Elevating Structures Halley V South Pole Research Station Can be jacked up View Direction Photo by BAS 12

13 Some Strategies Need Maintenance Time instance 1 Time instance 2 Existing Proposed 13

14 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 ) 14

15 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, sitespecific biases / complications, expensive G. Wiggs Laboratory wind tunnels Highly controlled environment, reproducible, limited sample sizes cause biases 15

16 Characteristics of aeolian sands 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. Taweelah D = mm Lahbab D = mm RAK South D = mm Approx. scale: 0 5 mm Khatim D = mm Hafeet D = mm 16

17 Meteorology Differs Across the Region Wind Speed (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. RKT DBX SHJ AUH AAN 17

18 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. This can be used to generate site-specific climate models. 18

19 Meteorology VU ~ m 3 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 m 3 m -1 yr -1 in northeastern Saudi Arabia, with a maximum of 29 m 3 m -1 yr -1 in high wind areas. 19

20 Computer Meteorology Models can Provide Annual Information 20

21 Meteorology & Sand Drift Risk Example: Annual hours above threshold (example year). Dubai Abu Dhabi Al Ain Liwa 21

22 Meteorology & Sand Drift Risk The data permits us to analyse the issues in new ways and greater detail 10 m Example: Annual flux potential in kg m -1 yr -1 (example year). 5 m 0 m In Egypt, the values exceed 40 m height: this is sand dune. 22

23 Sand Drift Risk Typical Sand Transport Statistics 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 Location 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 21 23

24 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 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), 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)

25 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

26 An optimal cross-section should encourage Deposition of sand upwind / away from the rail embankment Wind-porous track profiles can help reduce build up of sand reduce the carrying capacity of the wind Create an aerodynamically smooth surface Higher wind speeds over the track embankment and rails: accelerate wind accelerate the wind flow Ballast stone is a problem; not a solution. 27

27 Mitigation Theoretical Mitigation Option WIND c road Not to Scale - for illustrative purposes ONLY 28

28 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. 29

29 THANK YOU FOR YOUR KIND ATTENTION 30