Negative Impacts on Railway Embankments Exposed to Wind-Blown Sand and Optimizing

Mechanics, Materials Science & Engineering, May 2017

ISSN 2412-5954

24

Ahmed Abdelmoamen Khalil 1 Assistant Professor of Railway Engineering, Civil Engineering Department, Shoubra Faculty of Engineering, Benha University, Postal Code: 11629 Egypt a

ahmed.khalil@feng.bu.edu.eg DOI 10.2412/mmse.39.59.615 provided by Seo4U.link

Keywords: railway, embankment, track contamination, wind, sand, FLUENT.

ABSTRACT. Railway lines in deserts suffer from risks of migration of sand dunes, transport of sand by wind and its accumulation over the tracks. This paper focuses on causes, types, and different characteristics of sand movement in desert that affecting safety and performance of running trains. Risk and potential impact of accumulation of sand on Bahariya railway line located in Western Desert of Egypt such as; several derailments and contamination of track components are analysed. The purpose of this paper is to study the impact of embankment height on sand accumulation.

Thus, ANSYS FLUENT software is used to simulate the blown wind on the railway embankment to obtain the wind velocity vectors and contours. Hence, embankment height that reduces deposition and accumulation of sand over the track is obtained and recommended to 6 m. Cost analysis has been conducted to compare between the recent and the recommended embankments. It is concluded that cost of the recommended embankment is about 63% of the overall cost of the recent case.

Introduction. Wind is the main cause of sand movements, therefore; attention to the direction and the velocity of the winds is also of importance. Needs for attention to this issue is especially important when considering various preventive methods such as designing a wall [1]. In Egypt, sand deposits and other aeolian forms cover about 27% of the whole country [2]. Morphologically these landforms are subdivided into sand seas (ergs), isolated dunes and dune fields and sandy plains and sheets [2].

At several localities in Egypt, sand encroachment causes hazards to farmlands, highways, population centers and other infrastructures. According to [3], sand encroachment over the inhabitable areas of Egypt is classified into the following categories; (i) Severe dune migration ( > 15 m/year); it occurs in South Al-Bardaweil (North Sinai) and Kharga-Baris and Dakhla in the South Western Desert, (ii) Moderate dune migration (5 15 m/year); it prevails in Central Sinai, east of the Suez Canal, Siwa, Abu Mongar, Farafra, Bahariya and El Rayan; (iii) Slight dune migration ( < 5 m/year); it occurs on both sides of the Nile Delta, northern coast of the Nile Delta and along the Mediterranean Coastal Zone. Source of the sand in the Sahara Desert is attributed to the fluvial processes which thereafter reworked and deposited elsewhere by wind in later dryer ages [4].

Climate of western desert is too dry to have any rains. However the average value of rains is 3.6 mm/year. The average temperature is 29o C in the period from May to September in the north, but it raises up to 32o C in the south. Maximum temperature reaches 50o C. January is the coldest month in the year where the temperature reaches 13o C. However the minimum temperature lies between 0o C and 5o C. Wind blows from the north most of the year but it diverts to blow from the west in winter. The wind speed reaches 20 m/s and it is usually high in the spring, hence sandstorms are caused due to the high intensity of wind [5]. Railways had been established in the west desert of Egypt in 1900 when the government offered the Company of the Oases of West Deserts a concession to construct a railway line to connect the Oases with the Nile Valley. However, the company went 24

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bankrupt and the government seized the railway line in 1909. The line expanded from Mowasla station to Kasr Elkharga station with a length of 210 km.

When the mining communities have been established in the west desert, especially with emergence of iron and phosphorus ores, the railway transportation map has been changed where Egyptian State has constructed Bahariya railway line. This line carried iron ore from Bahariya mines to the steel factories in Helwan (South of Cairo). The line is also used to transport loamy clay from Oswan (South of Egypt) to station (km 48), as well as ballast from a query at station (km 66) to different locations in Egypt [6]. Nowadays, Bahariya railway line is a single track of length 346 km with 10 stations including the start station in Bahariya mines and the end station at Helwan. During the wind blowing period from November to end of April, sand which moves by the wind covers about 40% of the west desert surface. So, land transportation including Bahariya railway line crashes in this period of the year as shown in Fig. 1 [6]. This sand is transported by the wind which blows from the North-West direction with an average speed of 15 m/s [6]. Bahariya railway line is about to be closed during that period due to accumulation of sand over the tracks with average height of 0.10 m over the rail surface.

Thus, transportation of iron ore and other materials transferred to other transportation modes, e.g. roadways, which have high cost. This transformation causes many losses to the Authority of Egyptian National Railways (ENR) due to losing one of the most important sources of revenues.

Fig. 1. Bahariya railway track during the period of blowing sand.

It is also observed that accumulated sand affecting the track components with many negative impacts such as; increasing the rail surface roughness which causes wear to the rails and train wheels, wear and loosening of the rail fastening system. Because of those impacts, the train wheels are derailed causing many derailment accidents. The derailment accidents result also in severe defects and damages of the track sleepers and the whole stability of the track alignment. In addition to the damages of track components and instability of the track system, ENR provided the line with two sand sweepers and 7 loaders to remove the accumulated sand periodically. The annual deposited sand on the track is about 250,000 m3 [7]. As the equipment removes sand and distribute it alongside the railway line, the blown wind re-carries it causing re-covering the track. Investigation that carried by [1] shows, by studding the direction and the intensity of the wind and identifying the removal and sediment zones, one can design an optimize route through dunes with minimum dilemma. In [8] studied the accumulation of fine sand in canals network in Toshka project which located in western desert in Egypt. This researcher found that accumulation of fine sand is causing serious hydraulics and biological problems such as rising of bed level which in turn change the hydraulic characteristics of the canal (discharge, velocity, heads etc.). Also, the researcher recommended protecting means was determined for the most regions exposed to active sand dunes movement as follow design of MMSE Journal. Open Access www.mmse.xyz

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wind breaks, fixation the surface of one active sand dune by using stones on the sand dune surface against the most common wind directions and construction of trenches on the bank of El Sheik Zayed canal for trapping the moving sand.

This paper focuses on the negative impacts of wind- blown sand on the track of Bahariya railway line and contributes in finding an optimized solution to reduce these impacts. Thus, the following objectives are the core of this paper: a) Investigating and detecting the railway track to assess and analyze the impact of sand accumulation, b) Analyzing the wind simulation that has been carried out by the author using ANSYS FLUENT software to find out the effect of the embankment height, c) Determination of the optimized embankment height that reduces sand accumulation, d) Recommend and check cross section for side ditches to minimize sand accumulation over the track.

The applied research methodology in this paper is based on collecting the different statistical data from ENR reports, measurements and field observations of track deterioration and derailment accidents that have been caused by the wind blown sand; hence the negative impact is determined.

The author conducted a simulation using basics of Computational Fluid Dynamics (CFD) through ANSYS FLUENT software to analyze the impact of changing the embankment height and side slopes on deposition of sand above the railway track. This simulation generates wind velocity vectors and contours which indicate locations of sand deposition [9]. Also, a cost comparison between the recent and the recommended embankments is carried out to determine the effectiveness of the optimized embankment height.

Material and Methods Characteristics of Bahariya Railway Line Bahariya line is a single track of length 346 km with 10 stations including the start station in Bahariya mines and the end station at Helwan. Other eight stations take their names from their kilometrages, i.e. station 48, station 88, station 133, station 175, station 211, station 260, station 307, and station 328. Design speed of the line is 70 km/h and the operation speed is 50 km/h. Track is ballasted with continuous welded rails of UIC 54 and wooden sleepers. Most of the longitudinal profile is filling; hence the predominant depth of the embankment varies from 0.0 m to 2 m except three sections; from kilometrage 37 to kilometrage 44, from kilometrage 277 to kilometrage 281and from kilometrage 336 to kilometrage 346 where the depth is about 6 m. A sample of the longitudinal profile in a section of the predominant embankment and a typical cross section of the track are shown in Fig. 2 and Fig. 3 respectively (ENR, Design drawings of Bahariya railway line, unpublished).

Fig. 2. A Sample of Bahariya railway longitudinal profile.

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Fig. 3. Typical cross section of Bahariya railway track.

Field Statistics and Observations Train derailments that occurred from 1/1/ 2011 to 2/9/2014 due to rebounding of train wheels and sand accumulating above rails, their locations and costs in L.E are shown in Table 1 (ENR, Train`s accident monthly records, unpublished reports). Although, ENR has distributed some equipment to sweep sand; in addition to appointing special labors in some locations on the line, the efforts are not sufficient to keep the line performs adequately. Distribution of equipment and the required labors on the railway line is demonstrated in Table 2 (ENR, Bahariya railway line`s site technical records, unpublished reports).

Table 1. Statistics of Derailments from 1/1 2011 to 2/9/2014 and Costs in L.E. Year

2011

2012

2013

2014

No. of derailments/ year

10

6

12

8

Locations of derailments (km)

9.56 -23.4367.45 -103.2117.87-181.2219.18-259.40 275.90-301.29

23.90 -45.6765.32-69.90206.95301.84

8.80-21.43 - 65.34104.13-106.14 110.11-178.39 182.00 -219.70 305.10-311.21315.03

Delay cost

454125

272475

500272

310200

Derailments removal cost

420000

252000

470320

300015

Track repair cost

47212

31015

52500

27122

Source: ENR, Train`s accident monthly records, unpublished reports

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8.00 -19.8721.00 -206.50 211.32 - 219.06 258.46 -304.29

Mechanics, Materials Science & Engineering, May 2017

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Table 2. Distribution of equipment and the required labors on the railway line.

Station

Km48

Km88

Km211

Km260

Km307

Km328

Km340

Sand sweeper

1

1

-

-

-

-

-

Loader

1

1

1

1

1

1

1

Labors

3

4

2

3

2

2

4

Source: ENR, Bahariya railway line`s site technical records, unpublished reports Site visits have been done to detect and record the impact of sand accumulation on the track components deterioration and on the track stability. It is observed that there is a reduction in the thickness of rail seats especially in the location of heavy sand accumulation such as in km 36 and km 176. A loosening in the track fasteners (screw spikes) in those locations has been observed. A slight surface roughness and vertical wear on the rail head have been recorded as 1mm to 2mm. Also, it has been observed that track ballast contamination as a result of deposition of sand within the ballast, in addition to track buckling, i.e. a lateral movement. Distances in meters of worn rails, fasteners and contaminated ballast due to sand that have been changed according to ENR statistics are given in Table 3 [10]. The time intervals of closing the line due to blown sand and its removal costs are shown in Tables 4 and 5 respectively [10].

Table 3. Distances in Meters of Worn Rails, Fasteners and Contaminated Ballast.

Year

2011 2012 2013 2014

Rails

180

144

120

360

Ballast

540

810

650

900

Source: ENR, Maintenance Annual Statistical Reports, 2014 Table 4. Time Intervals of Closing the Line in Days.

Year

2011 2012 2013 2014

Time interval 60

93

80

70

Source: ENR, Maintenance Annual Statistical Reports, 2014 Table 5. Annual Cost of Sand Removal in L.E. Year Cost

2011

2012

3200000 3360000

2013

2014

3528000

3704000

Source: ENR, Maintenance Annual Statistical Reports, 2014 Simulation of Wind-Blown Sand on Embankment The wind flow is commonly studied experimentally, theoretically or numerically. An alternative to constructing a physical experiment is to perform a numerical analysis called (CFD) [9]. The govern equations of the numerical process are very complicated and should be solved simultaneously to provide solution. Therefore, the problem should be solved by making use of computers as a computational tool [11] and [12]. This involves taking a meshed geometry, and using a CFD software MMSE Journal. Open Access www.mmse.xyz

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package to create a simulation resembling the real world flow. The affected domain of the problem is discretized into a finite set of cells, which is called mesh or grid. Plots for contours and vectors are the output tools of examining the results of simulation [13]. Thus, a simulation has been constructed by the author based on CFD in ANSYS FLUENT using the wind roses and velocity field measurements that have been obtained and illustrated in Fig. 4 [5]. An average value of wind speed (15 m/s) has been set up in a height of 10 m above the embankment upper level of Bahariya railway line [5]. Properties of the wind- blown sand in the simulation process are described as follows: air density = 1.225 kg/m3, air viscosity = 1.85 * 10-5 and particle density = 1760 kg/m3 [14]. The boundary conditions and prepared mesh of the simulated model that have been used in processing the calculation by the software are shown in Fig. 5 and Fig. 6 respectively. The simulation output of the stream-wise velocity contours and vectors has been obtained for the predominant embankment cross sections of 2 m and 4 m heights and shown in Figs 7, 8, 9 and 10 respectively.

Fig. 4. Wind roses affecting Bahariya railway line [5].

Fig. 5. Boundary Conditions of the simulated model.

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Fig. 6. Prepared mesh for the simulated model.

Fig. 7. Contours of X velocity for 2.0 m height embankment.

Fig. 8. Velocity vectors for 2.0 m height embankment.

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Fig. 9. Contours of X velocity for 4.0 m height embankment.

Fig. 10. Velocity vectors for 4.0 m height embankment.

Results and Discussion. Records of derailments and their locations which are shown in Table 1 indicate that derailments have been occurred in locations of 2 m height embankment as it is noticed from the kilometrages where the accumulated sand is very heavy such that it covers the track including the running rails and track components. It is, also, observed from records in Table 2 that despite of the existence of the illustrated equipment and labor that have been appointed by ENR on the line, the derailments were not eliminated. Regarding the magnitude of accumulated quantities of sand, numbers of equipment and labor are not comparable.

Comparing the records of wear measurements of track components with the similar components on other lines of ENR, it is noticed that vertical wear values of Bahariya rails is higher. The main reason of that observation is the accumulation of sand over the track, which results in higher friction between train wheels and rail surface. It is also observed that a loss of material at the rail seat has been has led to track geometry problems such as gauge widening and loss of super-elevation.

Ballast contamination with sand that approaches the railway embankment due to deposition of sand within the ballast has been noticed in most of the line. This contamination reduces the adhesion forces, which are necessary to interlock the ballast grains. Thus, these types of track defects have increased the derailment risk by altering the ratio of lateral to vertical forces and consequently reducing the stability of the railway track. Because of problems associated with these defects and derailments, the service life of many sleepers in service on Bahariya railway line has been reduced.

Estimation of Different Costs Due to Blown Sand The financial impact of the blown sand can be categorized in 4 items: a) Cost of derailments, MMSE Journal. Open Access www.mmse.xyz

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b) Cost of track maintenance, c) Cost of sand removal, d) Cost of closing the line.

Total annual cost of derailments item (a) which is estimated from Table 1, and the average cost are given in Table 6.

Table 6. Total Annual and Average Costs of Derailments in L.E. Year

2011

2012

2013

2014

Cost of derailments

921,337

555,490

1,023,092

637,337

Average cost

784314

Cost of track maintenance (item b) includes changing the worn rails and contaminated ballast can be estimated as follows: Cost of changing one rail and its fasteners (18m) including the prices is 1200 L.E. Total lengths of changed rails and related fasteners in 4 years = 180+144+120+360 = 804 m Total lengths of changed ballast = 540+810+650+900 = 2900 m Volume of one meter length of ballast = 1.05 m3 3

Cost of changing 1m3 ballast = 150 L.E Thus, average annual cost of track maintenance = 241,200 +114,187.5 = 355,387.5 L.E Average annual cost of sand removal (item c) which is estimated from table 5 = 3,448,000 L.E Cost of closing the line (item d) is estimated according to closing time intervals which have been given in table 4 as follows: Cost of transporting 1 ton.km of iron ore = 0.25 L.E Total closed time = 60+93+80+70 = 303 days Total hauled distance = 345 km 21,000 L.E. Average annual cost of closing the line = 62,721,000/4 = 15,680,250 L.E Thus, the total average annual cost due to blown sand = 784,314 + 355,387.5 + 3,448,000 + 15,680,250 = 20,267,951.5 L.E. Analysis of Simulation Results The used CFD bases are upon that sand accumulates over the track in case of low friction velocities whereas in case of high friction velocities, the crossing wind will transport sand from one side to the other side without deposition over the track [11], [14], [15]. After the simulation was run; velocity contours which give visualization for the wind directions; were compared among the various cross section models. After comparing velocity contours, the velocity vectors which express the velocity magnitudes have been analyzed. According to fluid dynamic concepts, the lower magnitude of velocity causes larger quantities of sand deposition and vice versa. Analyzing the simulation results, MMSE Journal. Open Access www.mmse.xyz

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it is observed for the case of embankment of 2 m height that low friction velocity that represented by down contours and vectors (Fig. 7 and Fig. 8) is dominant and covered all the area including the railway track. For the case of embankment of 4 m height as obtained in Fig. 9 and Fig. 10, the friction velocity increases over the track; even though a low friction velocity exists over the area around the embankment and over the side slopes.

According to the bases of sand deposition that have given by CFD, the low friction velocity in the first case is due to very short height of the embankment which results in sever accumulation of sand over the track; whereas in the second case, the magnitude of friction velocity raises over the track.

Thus, wind transports the sand from the blowing direction to the other direction of the embankment with less accumulation of sand over the track. Result obtained in the second case assured that 4 m height of the embankment is not enough to eliminate sand accumulation over the track and whole embankment cross section. Therefore, other two suggested cases with 6 m height embankment accompanied with right and left ditches of variable slopes have been simulated. The elements of mesh which are processed by the software for this case are shown in Fig. 11. A side slope 3:2 for the ditches is shown in Fig. 12, but the nearest side slope of ditches to the embankment is suggested to be 6:1 as shown in Fig. 13. It is observed that raising height of embankment to 6 m and digging the ditches with side slope 6:1 contributed in minimizing the accumulation of sand over the track than the case of side slope 3:2, regardless the sand which has been accumulated in the ditches as shown in Figures 13 and 14.

To calculate the cost of raising the embankment to 6 m, it is assumed according to ENR prices in 2015 and referring to the cross section that is shown in Fig. 3: Required volume of earthworks to raise the embankment from 2 m to 6 m = 29,420 m3, thus total volume of 306 km = 9,002,520 m3, the price of 1 m3 = 67.98 L.E. Assuming that discount rates of initial cost equals the escalation rate of maintenance cost and life time of embankment = 70 years, thus, Average annual construction cost = 612,000,000/70= 8,742,857.14 L.E It is, also, assumed that quantity of removed sand from side ditches is the same as in the actual case without raising the embankment, so, Average annual cost of sand removal from ditches = 3,448,000 L.E.

Fig. 11. Elements of mesh size for case of 6 m.

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Fig. 12. Contours of X velocity for 6.0 m height embankment with suggested ditches of slope 3:2.

Fig. 13. Contours of X velocity for 6.0 m height embankment with suggested ditches of slope 6:1.

Fig. 14. Velocity vectors for 6.0 m height embankment with suggested ditches of slope 6:1.

To calculate the cost of raising the embankment to 6 m, it is assumed according to ENR prices in 2015 and referring to the cross section that is shown in Fig. 3: Required volume of earthworks to raise the embankment from 2 m to 6 m = 29,420 m3, thus total volume of 306 km = 9,002,520 m3, the price of 1 m3 = 67.98 L.E.

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Assuming that discount rates of initial cost equals the escalation rate of maintenance cost and life time of embankment = 70 years, thus, Average annual construction cost = 612,000,000/70= 8,742,857.14 L.E It is, also, assumed that quantity of removed sand from side ditches is the same as in the actual case without raising the embankment, so, Average annual cost of sand removal from ditches = 3,448,000 L.E. Cost Comparison To compare the costs which resulted from blown sand and raising the embankment, it is assumed that: - Rate of train derailment in the case of raising the embankment is considered as in the other lines which are not exposed to blown sand. This rate is found to be half the rate in the case of Bahariya railway line.

- Cost of track maintenance in the case of raising the embankment is half the cost in the case of Bahariya railway line. Therefore: Average annual cost of derailments in t Total annual cost in the case of raising the embankment = 8,742,857.14 + 3,448,000 +392,157+ 177,693.75 = 12,760,707.89 L.E Total annual cost in the case of raising the embankment / Total average annual cost due to blown sand Summary. The conducted simulation by ANSYS FLUENT in this paper concluded that: 1) The embankment height and side ditch slopes have a major effect on movement of wind and sand accumulation above the railway track.

2) The major reason of sand accumulation on the track is the short height of the embankment and those heights from 0 m to 4m are not adequate.

3) The optimized height of track embankment should be more than 4 m, thus the case of 6 m embankment height which is accompanied with side ditches will be proper for new lines.

Also, the cost analysis concluded that: 1) Total average annual cost due to negative impacts of wind- blown sand on Bahariya railway track is 20,267,951.5 L.E. 2) Total average annual cost of raising the height of embankment to 6 m is 12,760,707.89 L.E. Thus, the cost of raising the embankment is about 63% of the cost of negative impacts of wind- blown sand; therefore, raising the embankment to 6 m height is recommended to avoid consequences of wind- blown sand such as train derailments and track deterioration.

Acknowledgements I am grateful to engineer H. Fadel, the head of railway maintenance department in Cairo, as he provided me with the necessary technical reports and facilitate my site visits to Bahariya railway line.

I would also like to appreciate M. Salah, the chief engineer of Bahariya railway line who accompanied me in the site visits.

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[2] Gifford, A.W., Warner, D.M., and El-Baz, F. 1979. Orbital observations of sand distribution in the Western Desert of Egypt. Apollo-Soyuz Test Project Summary Science Report, vol. II, p. 219236.

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