Why do people spread stones along railroad tracks?

Certainly many of us wonder why the railroad tracks always have a layer of rubble spread evenly beneath the tracks. The known rail design includes 2 rails that are placed parallel and fixed on Traverse sleepers and all are placed on a three-layer stone (ballast). How important is this rock layer and why?

A layer of ballast stone is banded along the railroad tracks.

The real term "ballast" comes from the use of stones to crush sailboats and its function on rails is similar. When a train passes, the railroad will suffer a great amount of stress . It should be noted that 99% of the time the railroad tracks lie dormant, but 1% of the time is when it must "carry" an entire train. Take, for example, BHP Iron Ore's iron ore train in Western Australia, which is 7,353 km long, consisting of 682 bare cars, 8 GE AC6000 engines and weighs nearly 100,000 tons with 82,262 tons of ore and this is also the union. The longest and heaviest ship in the world according to Guinness Book of Records. The sleeper underneath helps to fix the rail to create a rail gauge and also has the function of transferring pressure from the rail to the ground below. To ensure that the pressure is evenly spread down while keeping the track stable under the dynamic load of a running ship, sleepers are placed on a ballast. In addition, rails are often exposed, so they face weather factors such as thermal expansion, ground movement, seismic, rain and many other natural factors such as weeds and wild plants. sprouting from below.

The world's longest and heaviest train BHP Iron Ore.

Since 200 years ago, railway engineers have begun to use a variety of materials to solve all these problems. In the past, iron slag and crushed coal were used as a base for the tracks. However, since the 1840s, paving stones have started to be widely used and become an important element in the rail structure. Paving stones are crushed stones of a size of less than 40 mm. They are sprayed under and around sleepers and possess a characteristic called " frictional inner rock aggregation ". This internal friction depends on the arrangement, shape and size of a small set of stones. Common types of hard rock are granite, quartz, trap stone, etc. If these stones are not available, sandstone and limestone can be used. How important is this internal friction ? To make it easier to imagine, think of a sand dune and a pile of stones with the same height. If you push the sand dune with your hand, you will find it easy to move. On the other hand, if you push the stone with your hand, you will feel the resistance . It is not easy to move the pile and it is even impassive even if you try your best. Similarly when you stand on a sand dune, it is easily crushed and when you stand on a pile of stones, it does not stop asthma. This is internal friction.

With this feature, three- piece stone provides a support platform, which helps increase rigidity, durability and flexibility for railroads when ships pass through. In addition, paving stones also help to bring rain and snow out of the tracks, prevent the appearance of water on the surface, prevent weeds and wild plants from growing on rails, increase the elasticity of the pre-rails for thermal impact.

Paving stones have high rigidity and high flexibility.

During construction, the thickness of the slab depends on the size and distance between the two rails (gauge), the flow of traffic on the route and many other factors. However, the three-layer stone should not be thinner than 150 mm and the tracks for high-speed trains may require a stone layer of up to half a meter thick. If the rock layer is not thick enough to overload the soil layer below, the worst case is that the track will sink. Slab is usually on a sub-ballast (above). This layer of stone acts as a water barrier and supports the upper rail structure. If the track has no extra ballast, the rail and sleepers may be flooded, damaged and lead to accidents for the ship.

Balfour Beatty Inc. A three-stone stone crushing, grinding and maintenance system.

Playing a very important role, three-layer stone rails are regularly maintained. If this layer of stone is dirty, the drainage efficiency will be reduced, causing the rubbish and dirt to be sucked from the auxiliary ballast layer to make this layer more dirty. Therefore, the paving stone always needs to be kept clean, firm or replaced with a variety of methods such as biology, labor or specialized machines.

The image of the railroad does not need to use stone slices.

In the face of the destruction of nature, people and wear and tear in the process of use, maintenance of the paving stones consumes a lot of manpower, cost and time. Therefore, the railway industry has also developed and applied railways without ballasts ( ballastless tracks ). Instead of using a three-layer slab of stone, concrete slabs are placed consecutively and the rail is placed directly on the top of the concrete slab. However, due to the higher initial cost and a long time to replace the existing railway lines, the non-stone rails are usually reserved for high-speed or heavy rail lines.

Through this column, we have partly understood the role of three-layer stone on rail. In the next sections, we will learn more about railway structure, rail gauge classification, rail design and sleepers.