Track ballast

The superstructure or track body of a railway line consists of the track bed and rails mounted thereon. The base forms a solid template for the construction of the superstructure, in which he compensates for unevenness of the terrain.

The superstructure, and in particular the track bed is used for absorption and distribution of forces caused by the mass, acceleration, sine run speed of the rail vehicles and thermal stress due to weather.

From the functionality of the upper and lower construction depend, among other things, the maximum speed of a track and the permissible axle load of the vehicles. Through so-called defects in the superstructure must be set up for safety speed restrictions that are detrimental to the travel times of trains and thus lead to delays.

In Germany, for compliance with the legal requirements of the Federal Railway Authority responsible for the maintenance and operation of the rail network DB Netz has been committed.

Construction

The superstructure includes a first track bed, which is usually of gravel. On these " ballasted " are transverse to the direction thresholds set on which the rails are fixed in the direction of travel. The fabricated usually made ​​of concrete, but often still made of wood or steel sleepers hold the rails in the designated distance, the track width to each other and have to continuously welded rails also caused by the thermal expansion forces are derived in the substructure.

On the thresholds rails are held in place by fasteners. In the simplest case, these are struck into the wood sleepers nails, which protrudes an edge of the T- head beyond an edge of the rail foot. Currently, i.d.R. Systems of threaded bolts, nuts and terminals used. In Germany, common attachment methods are on concrete sleepers, the superstructure W, on wooden sleepers, a variant of the superstructure K.

The ballast bed is flexible and helps to transmit both static and dynamic loads evenly across the base. Other advantages of a gravel bed are relatively good noise insulation and absorption of vibrations traveling through the sinus running trains arise. A gravel bed can maintain with simple means. Furthermore, a gravel bed performs the usual in Europe rainfall from the soil. The disadvantage is that it can be pulled up from the track bed at high speed rides gravel from draft of the moving train ( " flying ballast " ) and constitutes a danger to any nearby humans and animals as well as for technology.

In addition to the lower swelling by means of sleepers longitudinal sleepers are known. These are mounted in the longitudinal direction by two rails. This coach screws come with clamps, potting compound or jaws for fixing used. The application implies that the forces to be transmitted can be derived on a solid support to the substrate.

The track bed can also be made as slab track where the rails are mounted directly on an existing concrete or asphalt, fixed superstructure. The superstructure of concrete is mainly used in modern high-speed and high-speed lines while superstructures are used on asphalt base, primarily for trams that their driveways have to share with motor vehicle traffic. A solid track bed needed as an additional superstructure element soundproofing in the form of insulation blankets.

Care

The superstructure requires regular maintenance services to its duties to fulfill. Inadequate maintenance can decrease the load capacity of the track bed and the establishment of speed restrictions is the result.

Swell

Wooden sleepers start even with the best impregnation to rot at some point and then offer no more stable surface for the rails so that they are rarely more than lifetimes of 25 years. In special environments, such as in damp tunnels, test times can be much shorter. As the fasteners lose their hold in rotten sleepers, there may be trace extensions that can even lead to derailment.

Also age steel and concrete sleepers and therefore must be replaced in good time.

More recent developments on the one hand, the Y-shaped steel sleeper for normal superstructure, on the other hand the steel bridges threshold ( SBS) have, in this case, in terms of positional stability and length of stay, made ​​significant improvements. Both systems are designed so that a long hospital stay and less working off period is to be expected.

Gravel

Also the ballast needed care because always a perfect drainage of rain water must be ensured in the substructure. The easiest way is the application of herbicides by weeds trains, to prevent the coming of high vegetation. This can propel their roots to depths where normal soil under the gravel is.

The gravel needs its edges and gaps in order to fulfill its function properly. The wear of the edges can not be avoided by optimal choice of rock. Thus eventually the old dull gravel must be replaced by new sharp-edged. This is highly dependent on the load and desired position stability. Often it is sufficient to mix the old ballast with a new, in order to achieve the desired effect.

Is the water drain clogged with dirt, the dirt can not "breathe" and excessive plant growth can begin. Plants are a number of reasons in the track bed undesirable: For one, they hinder in addition to the flow of water, on the other thereby accumulates in the gravel with humus and becomes inflexible. Such vegetation is an occasion for the regular and necessary cleaning of the ballast. In this case, this is washed and re-used to a large extent. A flood may require replacement of the ballast because of the entry of suspended matter such as silt.

Because of the loose composite of the gravel stones with each other, these are driven apart over time. As a result, there are gaps in the track bed, which can no longer assume his duties. Smaller defects can be corrected manually by Nachstopfen. As a rule, tamping machines are used for repair. In this case, no ballast is replaced, but the lack of gravel topped up. Thus, the laterally displaced outwardly ballast must not be brought back to the desired position.

Rails

The rail itself must be regularly replaced because some abrasions can not fix by sanding with a sanding car you. The wait time of the outer rail in a helical tunnel of the Gotthard Railway is for example about three years. Also, the grinding can be carried out only a few times because some residual thickness of the rail head must be present. Also, micro- cracks, which by the constant alternating load the rail - if they are not detected in time - lead to a broken rail. For the early detection of damage the main routes are regularly worn by ultrasonic test car nowadays.

The former often encountered route goers today have been mostly replaced by vehicles, perform the necessary checks economical.