Track ballast forms the trackbed upon which railway sleepers (UK) or railroad ties A railroad tie is a rectangular object used as a base for railroad tracks. Ties are members generally laid transverse to the rails, on which the rails are supported and fixed, to transfer the loads from rails to the ballast and subgrade, and to hold the rails to the correct gauge (US) are laid. It is packed between, below, and around the ties.[1] It is used to facilitate drainage The earliest archaeological record of an advanced system of drainage comes from the Indus Valley Civilization from around 3100 BC in what is now Pakistan and North India. The ancient Indus systems of sewerage and drainage that were developed and used in cities throughout the civilization were far more advanced than any found in contemporary urban of water, to distribute the load from the railroad ties, and also to keep down vegetation Vegetation is the plant life or the plant ground cover of a region, not the particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader than the term flora which refers exclusively to species composition. Perhaps the closest synonym is plant community, but vegetation can, and that might interfere with the track structure.[1] This also serves to hold the track in place as the trains roll by. It is typically made of crushed stone Crushed stone or angular rock is a form of construction aggregate, typically produced by mining a suitable rock deposit and breaking the removed rock down to the desired size using crushers. It is distinct from gravel which is produced by natural processes of weathering and erosion, and typically has a more rounded shape. Angular crushed stone is, although ballast has sometimes consisted of other, less suitable materials. The term "ballast" comes from a nautical term for the stones used to stabilize a ship.[1]

Contents

Material properties

A good ballast should be strong, hard-wearing, stable, drainable, easy to clean, workable, resistant to deformation, easily available, and reasonably cheap to purchase.[2] Early railway engineers did not understand the importance of quality track ballast; they would use cheap and easily-available materials such as ashes, chalk, clay,[3] earth, and even cinders from locomotive fireboxes.[4] It was soon clear that good-quality ballast made of rock In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids was necessary if there was to be a good foundation and adequate drainage The earliest archaeological record of an advanced system of drainage comes from the Indus Valley Civilization from around 3100 BC in what is now Pakistan and North India. The ancient Indus systems of sewerage and drainage that were developed and used in cities throughout the civilization were far more advanced than any found in contemporary urban.[3]

Good quality track ballast is made of crushed natural rock with particles between 28mm and 50mm in diameter;[5] a high proportion of particles finer than this will reduce its drainage properties, and a high proportion of larger particles result in the load on the ties being distributed improperly.[5] Angular The angular is a large bone in the lower jaw of amphibians, birds and reptiles, which is connected to all other lower jaw bones: the dentary , the splenial, the suprangular, and the articular stones are preferable to naturally rounded Erosion is the process of weathering and transport of solids in the natural environment or their source and deposits them elsewhere. It usually occurs due to transport by wind, water, or ice; by down-slope creep of soil and other material under the force of gravity; or by living organisms, such as burrowing animals, in the case of bioerosion ones, as these interlock with each other, inhibiting track movement.[5][1] Soft materials such as limestone Limestone is a sedimentary rock composed largely of the mineral calcite . Like most other sedimentary rocks, limestones are composed of grains; however, most grains in limestone grains are skeletal fragments of marine organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and are not particularly suitable, as they tend to degrade under load when wet, causing deterioration of the line; granite Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granites usually have a medium to coarse grained texture. Occasionally some individual crystals (phenocrysts) are larger than the groundmass in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is sometimes known as a porphyry, although expensive, is one of the best materials in this regard.[5]

In the early days of railroads in the United States, much material for ballast came from rock found in the local area. In the Midwest, for example, much use was made of quartzite Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of iron oxide (Fe2O3), while states in the southeast, such as Florida, made use of limestone Limestone is a sedimentary rock composed largely of the mineral calcite . Like most other sedimentary rocks, limestones are composed of grains; however, most grains in limestone grains are skeletal fragments of marine organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and. One specific type of quartzite used in the Midwest earned the name "Pink Lady" due to its color;[6] in other areas, the ballast can be a mix of light and dark colors called "Salt and Pepper".

Construction

The thickness of a layer of track ballast depends on the size and spacing of the ties, the amount of traffic expected on the line, and various other factors.[1] Track ballast should never be laid down less than 150 mm (6 inches) thick;[5] high-speed railway lines may require ballast up to half a metre (20 inches) thick.[7] An insufficient depth of ballast overloads the underlying soil Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics; in the worst cases, this can cause the track to sink.[8] If the ballast is less than 300 mm (12 inches) thick, this can lead to vibrations, which can damage nearby structures (though increasing the depth beyond this has no measurable effect).[9]

Track ballast typically sits on a layer of sub-ballast; the latter is typically made of small crushed stones. It gives a solid support for the top ballast, and seals out water from the underlying ground.[1] Sometimes, an elastic mat is placed under the ballast layer as well; this can allow for significant reductions in vibration Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.[9]

It is essential for ballast to be piled as high as the ties, and for a substantial "shoulder" to be placed at their ends;[5] the latter being especially important, since this ballast shoulder is, for the most part, the only thing restraining lateral movement of the track.[10] The ballast shoulder should be at least 150 mm (6 inches) wide under any circumstances, and may be as large as 450 mm (18 inches).[11]

Maintenance

New track ballast is placed at the Boxmeer railway station, The Netherlands. A ballast regulator shaping newly placed ballast Ballast tamping machine as used in railroad track maintenance -- Dade City, Florida

If ballast is badly fouled, the clogging will reduce its ability to drain properly; this, in turn, causes more debris to be sucked up from the sub-ballast, causing more fouling.[12][7] Therefore, keeping the ballast clean is essential.

It is not always necessary to replace the ballast if it is fouled, nor must all the ballast be removed if it is to be cleaned. Removing and cleaning the ballast from the shoulder is often sufficient, if shoulder ballast is removed to the correct depth.[13][14] While this job was historically done by manual labour,[14] this process is now, like many other railway maintenance tasks, a mechanised Mechanization or mechanisation is providing human operators with machinery that assist them with the muscular requirements of work. It can also refer to the use of machines to replace automatic labor or animals. A step beyond mechanization is automation. Even the use of hand powered tools is an example of mechanization as it reduces the work of one,[15] with a chain of specially-designed railroad cars A railroad car or railway carriage is a vehicle on a rail transport system that is used for the carrying of cargo or passengers. Cars can be coupled together into a train and hauled by one or more locomotives. Passenger cars can be self propelled in which case they can be single or multiple units handling the task. One wagon cuts the ballast and passes it via a conveyor belt A belt conveyor consists of two or more pulleys, with a continuous loop of material - the conveyor belt - that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt forward. The powered pulley is called the drive pulley while the unpowered pulley is called the idler. There are two main industrial to a cleaning machine, then the cleaning wagon washes the ballast, and deposits the dirt and ballast into other wagons for disposal and re-use, respectively.[13] Such machines can clean up to two kilometres of ballast in an hour.[16]

Cleaning, however, can only be done a certain number of times before the ballast is damaged to the point that it cannot be re-used; furthermore, track ballast that is completely fouled can not be corrected by shoulder cleaning.[17] In such cases, it is necessary to replace the ballast altogether. One method of "replacing" ballast, if necessity demands, is to simply dump fresh ballast on the track, jack the whole track on top of it, and then tamp it down;[14] alternatively, the ballast underneath the track can be removed with an undercutter, which does not require removing or lifting the track.[17]

Regular inspection of the ballast shoulder is important;[5] as noted earlier, the lateral stability of the track depends upon the shoulder. The shoulder acquires some amount of stability over time, being compacted by traffic; maintenance tasks such as replacing ties, tamping, and ballast cleaning can upset this stability. After performing these tasks, it is necessary for either trains to run at reduced speed on the repaired routes, or to employ machinery to compact the shoulder again.[18][19]

If the trackbed becomes uneven, it is necessary to pack ballast underneath sunk ties to level the track out again. This is, in the mechanized age, usually done by a ballast tamping machine. A more recent, and probably better,[7] 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 void. This has the advantage of not disturbing the well-compacted ballast on the trackbed, as tamping is likely to do.[20] This technique is called pneumatic ballast injection (PBI; or, less formally, "stoneblowing"[21]). However, this technique is not as effective with fresh ballast, as the smaller stones tend to move down between the larger pieces of ballast.[16]

References

Notes

  1. ^ a b c d e f Solomon 2001, p. 18.
  2. ^ Hay 1982, pp. 409-410.
  3. ^ a b Bonnett 2005, p. 59.
  4. ^ Solomon 2001, p. 60.
  5. ^ a b c d e f g Bonnett 2005, p. 60
  6. ^ Solomon 2001, p. 19.
  7. ^ a b c Bell 2004, p. 396.
  8. ^ Hay 1982, p. 399.
  9. ^ a b Bachmann 1997, p. 121.
  10. ^ Hay 1982, p. 407.
  11. ^ 150 mm is considered an absolute minimum, and 300 mm (12 inches) being recommended for use in heavy traffic, or with continuous welded rail Rail tracks (more commonly: railway tracks , railroad tracks or train tracks (US)) are the surface structures that support and guide trains or other rail-guided transportation vehicles or concrete ties. Most railways use between 300 mm and 400 mm (16 inches). A 450 mm shoulder significantly increases lateral stability and reduces maintenance effort, though little or no resistance to buckling is gained with a shoulder above this size. See Hay 1982, pp. 407-408; Kutz 2004 24.4.2.
  12. ^ Solomon 2001, p. 40.
  13. ^ a b Selig & Waters 1994, p. 1430.
  14. ^ a b c Solomon 2001, p. 41.
  15. ^ Institution of Civil Engineers 1988, p. 231.
  16. ^ a b IFSC #37, ch. 9.
  17. ^ a b Solomon 2001, p. 43.
  18. ^ Hay 1982, p. 408.
  19. ^ Kutz 2004, 24.4.2.
  20. ^ Anderson & Key 1999.
  21. ^ Ellis 2006, Pneumatic Ballast Injection, p. 265.

Sources

See also

External links

Further reading

New South Wales: Ballast 1850-1987 Longworth, Jim Australian Railway History Australian Railway History , is the premier magazine covering railway history in Australia. It is published monthly by the New South Wales Division of the Australian Railway Historical Society on behalf of the seven state and territory Divisions, December, 2004 pp443-462

Rail tracks Rail tracks (more commonly: railway tracks , railroad tracks or train tracks (US)) are the surface structures that support and guide trains or other rail-guided transportation vehicles
Track parts Axe ties • Breather switch • Chair (railway) • Datenail • Fishplate • Pandrol • Permanent way The permanent way is the elements of railway lines: generally the pairs of rails typically laid on ties embedded in ballast, intended to carry the ordinary trains of a railway. It is described as permanent way because in the earlier days of railway construction, contractors often laid a temporary track to transport spoil and materials about the • Rail fastening system • Rail profile In all but very early cast rails a rail is hot rolled steel profile of a specific shape or cross section designed for use as the fundamental component of railway track • Rail spike • Railroad tie A railroad tie is a rectangular object used as a base for railroad tracks. Ties are members generally laid transverse to the rails, on which the rails are supported and fixed, to transfer the loads from rails to the ballast and subgrade, and to hold the rails to the correct gauge • Railroad switch • Tie plate • Track ballast

Categories: Rail infrastructure Categories: Rail transport | Transport infrastructure

 

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