Have you wondered what a ballast is and its functions? If yes, then you have gotten to the right place. This article will be discussing on ballast, the advantages and disadvantages of ballast, types of ballast and their benefits.
Ballast is a granular material which is placed and packed below and around the railway sleepers. It can be gravel, sand, coal dust. Ballast stabilizes the track and provides some degree of drainage. It also bears the weight of locomotives, rolling stock, and associated tracks equipment above.
The main purpose of ballast is to achieve a good running track and keep the track work in place. Ballast is usually placed on top of the subgrade. A good ballasted track should be hard wearing, have a smooth surface, be able to carry heavy loads and able to drain properly.
The railway sleepers and the ballast jointly form a track structure which is designed to withstand the dynamic loads generated by trains or other traffic passing over it, so that it maintains its stability even through years of usage. This sub grade supports sleepers and rail soon after sleepers are laid in place.
What Is Ballast?
In case you want to know what is ballast let’s start from the beginning.
A rail track has different components; rails, ties, sleepers, ballast and sometimes bridges etc. All these components works together in the support of railway tracks which keeps the tracks in place and allows smooth movement from one point to another.
A rail consists of four parts:
The first part is a steel rail that is inserted between two layers of wood to form a sandwich plank. The second part is the iron strip called throat plate set into wooden sleepers. The third part is ties that are nailed onto the sleepers.
And finally, ballast which has the role of supporting the track so that it will remain in place through years of usage.
The throat plate is a rectangular plate made of iron. It is set into the sleeper to provide a smooth surface for roller bearing to run over. The sleeper provides a wooden bearing between the rails and ties, preventing lateral movement and guiding the wheel flange along track centre line.
The tie secures rails to sleepers and provides an anchor for ballast. This prevents longitudinal movement and ensures correct gauge of track i.e., distance between two adjacent rails.
The wooden sleepers provide stability and strength for the track and are set behind the track. They have nails with heads and lengths on them which secure them into place and allow the sleepers to support the weight of locomotives and trains.
Ballast consists of loose stones, crushed or pulverized stone, sand, gravel, small rock particles etc., usually mixed with some kind of binding substance such as asphalt or cement mortar, etc. Ballast comes in different sizes and shapes depending on the application requirements.
Apart from supporting rails and ties, the ballast provides drainage and the sub grade for track work. It bears the load of vehicles on top of it, and it drains rain water.
Now that we have known what the meaning of ballast, let’s have a look at the advantages and disadvantages of ballast.
Advantages And Disadvantages Of Ballast
Going into the advantages and disadvantages of ballast, we will be looking firstly at the advantages of ballast and later the disadvantages of ballast.
Advantages Of Ballast
A ballasted railway track has several advantages like it does not loose its original height over time (due to external forces), does not erode easily, does not allow water to flow through its bed etc.
Some of the main advantages of ballast includes:
- The advantage is that it provides a lot of weight to help stabilize the track which is needed for heavy trains or equipment to go on them.
- Another advantage is that ballast has drainage properties which keep your railroad from flooding.
- Another advantage is that ballasts could be laid directly on rocks without first having to remove the rocks. If you are laying a ballasted track, you don’t need to remove the underlying rock, just lay ballast and rails on it.
- Other advantages of ballast includes it lessens the effect of external forces, increases drainage and reduces the effect of earthquakes.
Now with the advantages of ballast, let’s have a look at the disadvantages of ballast.
Disadvantages Of Ballast
The major disadvantage of ballast is that it is hard to repair when defective. The tracks are heavy and cost a lot to replace especially when steel or manganese ones are used. When damage occurs in track work, rails or sleepers are easily replaced but it is not possible to repair damaged ballast due to its irregular shape and different sizes.
There are several other disadvantages of ballast which includes:
- Cost: it is costly to purchase and lay ballast, and repair when damaged.
- Harder to lay: if you want to place a rail track on a slope, ballast will require more work as compared to sleepers.
- Causes noise pollution: some materials used for ballast such as crushed glass and concrete, can cause noise pollution.
- Harder to maintain: it is more expensive to maintain a ballasted track than a sleeper track due to the use of special tools and skills required for smoothing the ballast surface etc.
Before any track work is undertaken to place any kind of ballast, an assessment must be carried out to determine if ballasting should take place. This is to ensure that all railway tracks are in good condition and repair before ballasting works commence.
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There are several methods used to assess the feasibility of ballast placement.
- Level gauge: it is used to determine the existing rail level with respect to track center level i.e., height of rails above the ground or other reference lines or surfaces. This gauge is obtained from a leveled track bed, superimposed on a drawing of rail profile, sleeper and sub grade thicknesses and projected onto the top of rail curves for measurement.
- Profile gauge: it is used to determine the existing rail profile with respect to track centerline i.e., vertical height of cross sections or curves above the ground or other reference lines or surfaces.
It is obtained from a leveled track bed, superimposed on a drawing of rail profile, sleeper and sub grade thicknesses and project on the top of rail curves for measurement.
- Profile indicator: it is used to measure existing angle between rail and track centerline i.e., vertical angle at which top and bottom of rail cross section meets the sub grade surface.
- Ideal gauge: it is used to measure rail profile with respect to track centerline, obtained from a leveled grade which can be obtained by a simple job like leveling a track bed and measuring the difference in height between two adjacent rails.
If level gauge, profile gauge and ideal gauge are not available, then other methods can be used for determining rail level such as leveling the track bed, taking measurements of existing rails at different levels and calculating the difference in height between them and then projecting these measurements onto the top of curves or profile.
Moving onwards, now we have made mention of the advantages and disadvantages of ballast and the methods involved, let’s also talk about the application of ballast.
Applications Of Ballast
Railway track is a huge network spread in different parts of the world. Usually, it consists of two parallel tracks on which trains run in opposite directions. The most common forms of ballast used are crushed stones and fine sand.
Some railways use other materials such as cinders and gravels. When gravels and cinders are used as ballast, they are mixed with bituminous compounds such as tar to enhance their strength and water resistance.
To lay the rails on bed of ballast, it is necessary to prepare a bed that can support rails and sleepers. This can be achieved by using ground granulated blast furnace slag (GGBS). This is known as ballast, it is the mixture of cement, sand and clay that can be used to bed a railway track.
Before preparation of ballast, it is necessary to check whether the subgrade soil and existing ground conditions are suitable to support the load of rail tracks. This can be achieved by performing a geotechnical evaluation.
Nowadays, it is not possible to prepare ballast directly on rock because rocks have various characteristics, which can also be affected by climate condition and weathering. So ballast has to be prepared in such a way that it suits on all type of soils.
This article has discussed the advantages and disadvantages of ballast and its applications. Hopefully, this article has helped you to understand ballast aesthetically.
The term “ballast” in the railway context refers to rocks and boulders used to stabilize tracks and prevent them from shifting. This has been around since the early days of railroads. In the 19th century, ballast was often made from rocks and boulders.
Due to the superior drainage property that it provides, this ballast is still widely used by railroads today. In addition to rock ballast, there are other different types of ballast which include gravel, sand, broken stone, bricks and moorum.
The easiest way of laying tracks on flat ground is through the use of fine sand or crushed stone base.
The determination of track location was done by leveling on grades such as rail bed and gradually placing successive courses of rails on beds – one over the other, until about three courses were laid.