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Track ballast

January 01, 1970

For other uses, see Ballast (disambiguation).

Track ballast is the material which forms the trackbed upon which railroad ties (UK: sleepers) are laid. It is packed between, below, and around the ties.[1] It is used to bear the compression load of the railroad ties, rails, and rolling stock; to facilitate drainage; and keep down vegetation that can compromise the integrity of the combined track structure.[1] Ballast also physically holds the track in place as the trains roll over it. Not all types of railway tracks use ballast.[2]

Good quality track ballast is made of crushed stone. The sharp edges help the particles interlock with each other.
Track ballast supports railway sleepers, which carry railway track.

A variety of materials have been used as track ballast, including crushed stone, washed gravel, bank run (unwashed) gravel, torpedo gravel (a mixture of coarse sand and small gravel), slag, chats, coal cinders, sand,[3] and burnt clay.[4] The term "ballast" comes from a nautical term for the stones used to stabilize a ship.[1]

Construction edit

The appropriate thickness of a layer of track ballast depends on the size and spacing of the ties, the amount of traffic on the line, and various other factors.[1] Track ballast should never be laid down less than 150 mm (6 inches) thick,[5] and high-speed railway lines may require ballast up to 0.5 metres (20 inches) thick.[6] An insufficient depth of ballast causes overloading of the underlying soil, and in unfavourable conditions, overloading the soil causes the track to sink, usually unevenly.[7] Ballast less than 300 mm (12 inches) thick can lead to vibrations that damage nearby structures. However, increasing the depth beyond 300 mm (12 inches) confers no extra benefit in reducing vibration.[8]

In turn, track ballast typically rests on a layer of sub-ballast, small crushed stones which provide a solid support for the top ballast and reduces ingress of water from the underlying ground.[1] Sometimes an elastic mat is placed between the sub-ballast and ballast, significantly reducing vibration.[8]

It is essential for ballast to both cover the ties and form a substantial "shoulder"[5] to restrain lateral movement of the track.[9] This shoulder should be at least 150 mm (6 inches) wide, and may be as wide as 450 mm (18 inches).[10] Most railways use between 300 and 400 mm (12 and 16 inches).

 
Ballast must be irregularly shaped to work properly.

Stones must be irregular, with sharp edges to ensure they properly interlock with each other and the ties to fully secure them against movement. Speed limits are often reduced for a period of time on sections of track where fresh ballast has been laid in order to allow it to properly settle.[11]

Ballast can only be cleaned so often before it is damaged beyond re-use. Ballast that is completely fouled can not be corrected by shoulder cleaning.[12] One method of "replacing" ballast is to simply dump fresh ballast on the track, jack the whole track on top of it, and then tamp it down.[13] Alternatively, the ballast underneath the track can be removed with an undercutter, which does not require removing or lifting the track.[12]

The dump and jack method cannot be used through tunnels, under bridges, or where there are platforms. Where the track is laid over a swamp the ballast is likely to sink continuously, and needs to be "topped up" to maintain its line and level. After 150 years of topping up at Hexham, Australia, there appears to be 10 m (33 ft) of sunken ballast under the tracks.[14] Chat Moss in the United Kingdom is similar.[citation needed]

Regular inspection of the ballast shoulder is important.[5] The shoulder acquires some amount of stability over time, being compacted by traffic, but maintenance tasks such as replacing ties, tamping, and ballast cleaning can upset that stability. After performing those tasks, it is necessary either for trains to run at reduced speed on the repaired sections, or to employ machinery to compact the shoulder again.[15][16]

If the trackbed becomes uneven, it is necessary to pack ballast underneath sunken ties to level the track again, which is usually done by a ballast tamping machine. A more recent, and probably better,[6] technique is to lift the rails and ties, and to force stones, smaller than the track ballast particles and all of the same size, into the gap. That has the advantage of not disturbing the well-compacted ballast on the trackbed, which tamping is likely to do.[17] The technique is called pneumatic ballast injection (PBI), or, less formally, "stoneblowing".[18] However, it is not as effective as fresh ballast, because the smaller stones tend to move down between the larger pieces of ballast and degrade its bonds.[19]

Quantities edit

The quantity of ballast used tends to vary with gauge, with the wider gauges tending to have wider formations, although one report states that for a given load and speed, narrowing the gauge only slightly reduces the quantity of earthwork and ballast needed. The depth of ballast also tends to vary with the density of rail traffic, as faster and heavier traffic requires greater stability. The quantity of ballast also tends to increase over the years as more and more ballast is piled onto an existing roadbed. Some figures from an 1897 report listing requirements for light railways (usually narrower than standard gauge) are:

  • first class line – 60 lb/yd (29.8 kg/m) rail – 1,700 cu yd/mi (810 m3/km).
  • second class line – 41.5 lb/yd (20.6 kg/m) rail – 1,135 cu yd/mi (539 m3/km).
  • third class line – 30 lb/yd (14.9 kg/m) rail – 600 cu yd/mi (290 m3/km).[20]

See also edit

Footnotes edit

  1. ^ a b c d e Solomon (2001), p. 18.
  2. ^ Tubular Modular Track
  3. ^ Kellogg, H. W. (1946). "Selection and Maintenance of Ballast" (PDF). American Railway Engineering and Maintenance-of-Way Association. Retrieved 27 March 2021.
  4. ^ Beyer, S. W.; Williams, I. A. (1904). . pp. 534–537. Archived from the original on 13 August 2010.
  5. ^ a b c Bonnett (2005), p. 60.
  6. ^ a b Bell 2004, p. 396.
  7. ^ Hay (1982), p. 399.
  8. ^ a b Bachmann 1997, p. 121.
  9. ^ Hay (1982), p. 407.
  10. ^ 150 mm (6 inches) is with 300 mm (12 inches) recommended for use in heavy traffic, or with continuous welded rail or concrete ties. A 450 mm (18 in) shoulder significantly increases lateral stability and reduces required maintenance, though little or no resistance to buckling is gained above this size. See Hay 1982, pp. 407–408; Kutz 2004, Section 24.4.2.
  11. ^ Bibel, George (2012). Train Wreck: The Forensics of Rail Disasters. Baltimore, MD: Johns Hopkins University Press. pp. 287–88. ISBN 9781421405902.
  12. ^ a b Solomon 2001, p. 43.
  13. ^ Solomon (2001), p. 41.
  14. ^ Nasir, Enamul. "Railway Materials Case Study". Retrieved 4 August 2016.
  15. ^ Hay 1982, p. 408.
  16. ^ Kutz (2004), Section 24.4.2.
  17. ^ Anderson & Key (1999).
  18. ^ Ellis (2006), p. 265, Pneumatic Ballast Injection
  19. ^ IFSC #37, ch. 9.
  20. ^ "LIGHT RAILWAYS". The Brisbane Courier. National Library of Australia. 29 September 1897. p. 5. Retrieved 21 May 2011.

References edit

  • Anderson, W. F.; Key, A. J. (1999). "Two layer ballast beds as railway track foundations". Twelfth European Conference on Soil Mechanics and Geotechnical Engineering (Proceedings). AA Balkema. ISBN 90-5809-047-7.
  • Bachmann, Hugo; et al. (1997). Vibration Problems in Structures: Practical Guidelines. Birkhäuser. ISBN 3-7643-5148-9.
  • Bell, F.G. (2004). Engineering Geology and Construction. Spon Press. ISBN 0-415-25939-8.
  • Bonnett, Clifford F. (2005). Practical Railway Engineering (2nd ed.). London, UK: Imperial College Press. ISBN 978-1-86094-515-1. OCLC 443641662.
  • Ellis, Iain (2006). Ellis' British Railway Engineering Encyclopaedia. Lulu.com. ISBN 1-84728-643-7.[better source needed]
  • Hay, William Walter (1982). Railroad Engineering. John Wiley and Sons. ISBN 0-471-36400-2.
  • Indraratna, Buddhima (2011). Advanced rail geotechnology--ballasted track. Leiden, The Netherlands: CRC Press/Balkema. ISBN 978-0-203-81577-9.
  • Institution of Civil Engineers (1988). Urban Railways and the Civil Engineer. Thomas Telford. ISBN 0-7277-1337-X.
  • International Federation for Structural Concrete (fédération internationale du béton) bulletin #37.
  • Kutz, Myer (2004). Handbook of Transportation Engineering. McGraw-Hill. ISBN 0-07-139122-3.
  • Selig, Ernest Theodore; Waters, John M. (1994). Track Geotechnology and Substructure Management. Thomas Telford. ISBN 0-7277-2013-9.
  • Solomon, Brian (2001). Railway Maintenance Equipment: The Men and Machines that Keep the Railroads Running. MBI Publishing Company. ISBN 0-7603-0975-2.

Further reading edit

External links edit

 
Wikimedia Commons has media related to Ballast.
  • Photos of ballast cleaners in the UK
  • Photos of ballast regulators in the UK

January 01, 1970
track, ballast, other, uses, ballast, disambiguation, material, which, forms, trackbed, upon, which, railroad, ties, sleepers, laid, packed, between, below, around, ties, used, bear, compression, load, railroad, ties, rails, rolling, stock, facilitate, drainag. For other uses see Ballast disambiguation Track ballast is the material which forms the trackbed upon which railroad ties UK sleepers are laid It is packed between below and around the ties 1 It is used to bear the compression load of the railroad ties rails and rolling stock to facilitate drainage and keep down vegetation that can compromise the integrity of the combined track structure 1 Ballast also physically holds the track in place as the trains roll over it Not all types of railway tracks use ballast 2 Good quality track ballast is made of crushed stone The sharp edges help the particles interlock with each other Track ballast supports railway sleepers which carry railway track A variety of materials have been used as track ballast including crushed stone washed gravel bank run unwashed gravel torpedo gravel a mixture of coarse sand and small gravel slag chats coal cinders sand 3 and burnt clay 4 The term ballast comes from a nautical term for the stones used to stabilize a ship 1 Contents 1 Construction 2 Quantities 3 See also 4 Footnotes 5 References 6 Further reading 7 External linksConstruction editThe appropriate thickness of a layer of track ballast depends on the size and spacing of the ties the amount of traffic on the line and various other factors 1 Track ballast should never be laid down less than 150 mm 6 inches thick 5 and high speed railway lines may require ballast up to 0 5 metres 20 inches thick 6 An insufficient depth of ballast causes overloading of the underlying soil and in unfavourable conditions overloading the soil causes the track to sink usually unevenly 7 Ballast less than 300 mm 12 inches thick can lead to vibrations that damage nearby structures However increasing the depth beyond 300 mm 12 inches confers no extra benefit in reducing vibration 8 In turn track ballast typically rests on a layer of sub ballast small crushed stones which provide a solid support for the top ballast and reduces ingress of water from the underlying ground 1 Sometimes an elastic mat is placed between the sub ballast and ballast significantly reducing vibration 8 It is essential for ballast to both cover the ties and form a substantial shoulder 5 to restrain lateral movement of the track 9 This shoulder should be at least 150 mm 6 inches wide and may be as wide as 450 mm 18 inches 10 Most railways use between 300 and 400 mm 12 and 16 inches nbsp Ballast must be irregularly shaped to work properly Stones must be irregular with sharp edges to ensure they properly interlock with each other and the ties to fully secure them against movement Speed limits are often reduced for a period of time on sections of track where fresh ballast has been laid in order to allow it to properly settle 11 Ballast can only be cleaned so often before it is damaged beyond re use Ballast that is completely fouled can not be corrected by shoulder cleaning 12 One method of replacing ballast is to simply dump fresh ballast on the track jack the whole track on top of it and then tamp it down 13 Alternatively the ballast underneath the track can be removed with an undercutter which does not require removing or lifting the track 12 The dump and jack method cannot be used through tunnels under bridges or where there are platforms Where the track is laid over a swamp the ballast is likely to sink continuously and needs to be topped up to maintain its line and level After 150 years of topping up at Hexham Australia there appears to be 10 m 33 ft of sunken ballast under the tracks 14 Chat Moss in the United Kingdom is similar citation needed Regular inspection of the ballast shoulder is important 5 The shoulder acquires some amount of stability over time being compacted by traffic but maintenance tasks such as replacing ties tamping and ballast cleaning can upset that stability After performing those tasks it is necessary either for trains to run at reduced speed on the repaired sections or to employ machinery to compact the shoulder again 15 16 If the trackbed becomes uneven it is necessary to pack ballast underneath sunken ties to level the track again which is usually done by a ballast tamping machine A more recent and probably better 6 technique is to lift the rails and ties and to force stones smaller than the track ballast particles and all of the same size into the gap That has the advantage of not disturbing the well compacted ballast on the trackbed which tamping is likely to do 17 The technique is called pneumatic ballast injection PBI or less formally stoneblowing 18 However it is not as effective as fresh ballast because the smaller stones tend to move down between the larger pieces of ballast and degrade its bonds 19 Quantities editThe quantity of ballast used tends to vary with gauge with the wider gauges tending to have wider formations although one report states that for a given load and speed narrowing the gauge only slightly reduces the quantity of earthwork and ballast needed The depth of ballast also tends to vary with the density of rail traffic as faster and heavier traffic requires greater stability The quantity of ballast also tends to increase over the years as more and more ballast is piled onto an existing roadbed Some figures from an 1897 report listing requirements for light railways usually narrower than standard gauge are first class line 60 lb yd 29 8 kg m rail 1 700 cu yd mi 810 m3 km second class line 41 5 lb yd 20 6 kg m rail 1 135 cu yd mi 539 m3 km third class line 30 lb yd 14 9 kg m rail 600 cu yd mi 290 m3 km 20 See also edit nbsp Trains portal Ballastless track Ballast tamper Gandy dancer Maintenance of way Track maintenanceFootnotes edit a b c d e Solomon 2001 p 18 Tubular Modular Track Kellogg H W 1946 Selection and Maintenance of Ballast PDF American Railway Engineering and Maintenance of Way Association Retrieved 27 March 2021 Beyer S W Williams I A 1904 The Geology of Clays pp 534 537 Archived from the original on 13 August 2010 a b c Bonnett 2005 p 60 a b Bell 2004 p 396 Hay 1982 p 399 a b Bachmann 1997 p 121 Hay 1982 p 407 150 mm 6 inches is with 300 mm 12 inches recommended for use in heavy traffic or with continuous welded rail or concrete ties A 450 mm 18 in shoulder significantly increases lateral stability and reduces required maintenance though little or no resistance to buckling is gained above this size See Hay 1982 pp 407 408 Kutz 2004 Section 24 4 2 Bibel George 2012 Train Wreck The Forensics of Rail Disasters Baltimore MD Johns Hopkins University Press pp 287 88 ISBN 9781421405902 a b Solomon 2001 p 43 Solomon 2001 p 41 Nasir Enamul Railway Materials Case Study Retrieved 4 August 2016 Hay 1982 p 408 Kutz 2004 Section 24 4 2 Anderson amp Key 1999 Ellis 2006 p 265 Pneumatic Ballast Injection IFSC 37 ch 9 LIGHT RAILWAYS The Brisbane Courier National Library of Australia 29 September 1897 p 5 Retrieved 21 May 2011 References editAnderson W F Key A J 1999 Two layer ballast beds as railway track foundations Twelfth European Conference on Soil Mechanics and Geotechnical Engineering Proceedings AA Balkema ISBN 90 5809 047 7 Bachmann Hugo et al 1997 Vibration Problems in Structures Practical Guidelines Birkhauser ISBN 3 7643 5148 9 Bell F G 2004 Engineering Geology and Construction Spon Press ISBN 0 415 25939 8 Bonnett Clifford F 2005 Practical Railway Engineering 2nd ed London UK Imperial College Press ISBN 978 1 86094 515 1 OCLC 443641662 Ellis Iain 2006 Ellis British Railway Engineering Encyclopaedia Lulu com ISBN 1 84728 643 7 better source needed Hay William Walter 1982 Railroad Engineering John Wiley and Sons ISBN 0 471 36400 2 Indraratna Buddhima 2011 Advanced rail geotechnology ballasted track Leiden The Netherlands CRC Press Balkema ISBN 978 0 203 81577 9 Institution of Civil Engineers 1988 Urban Railways and the Civil Engineer Thomas Telford ISBN 0 7277 1337 X International Federation for Structural Concrete federation internationale du beton bulletin 37 Kutz Myer 2004 Handbook of Transportation Engineering McGraw Hill ISBN 0 07 139122 3 Selig Ernest Theodore Waters John M 1994 Track Geotechnology and Substructure Management Thomas Telford ISBN 0 7277 2013 9 Solomon Brian 2001 Railway Maintenance Equipment The Men and Machines that Keep the Railroads Running MBI Publishing Company ISBN 0 7603 0975 2 Further reading editNew South Wales Ballast 1850 1987 Longworth Jim Australian Railway History December 2004 pp443 462External links edit nbsp Wikimedia Commons has media related to Ballast Photos of ballast cleaners in the UK Photos of ballast regulators in the UK Retrieved from https en wikipedia org w index php title Track ballast amp oldid 1199081215, wikipedia, wiki, book, books, library,

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