Ballastless Track

The technical concept of a railway track consisting of ballast, sleepers, and rails is very old and has stood the test of time. Such a system is simple and can be rapidly extended, renewed, or dismantled. The general problem that occurs with ballasted tracks is that the ballast material slowly deteriorates due to the load of the traffic. The breaking of the ballast under the pressure exerted by the load causes geometrical unevenness and clogging of the ballast bed by fine particles. Therefore, regular maintenance is needed to restore track alignment. The experience in Germany and other countries has been that the conventional track may be used for speeds of up

to 250 km/h but not beyond that. For higher speeds, the construction of a ballastless track is required. In a ballastless track, the rails are directly fastened to the concrete slab using elastic fastenings. A ballastless track is expensive but is likely to require little or no maintenance during its lifetime. The success of a ballastless track is primarily based on the following advantages it offers.

Stability, precision, and comfort A ballastless track assures a permanently stable track and can withstand the heavy load of high-speed train traffic. Its performance is characterized by top quality, functionality and safety. The precise adjustment of the track up to the last millimetre while it is being assembled at the construction site is the prerequisite for ride comfort as well as reduction of pressure loads experienced by the rolling stock.

Long life-span with practically no maintenance With a service life of at least 60 years and with little or no requirement for service or maintenance, a ballastless track offers great viability and unmatched cost effectiveness in high-speed operations.

Flexibility and end-to-end effectiveness in application With its comparatively low structural height and the possibility of the achievement of the optimal track alignment, ballastless track technology offers highly attractive and beneficial solutions as an end-to-end system technology for main-track and turnout sections. This technology can be applied on a uniform basis on embankments, bridges, and tunnels.

Basis for optimal routing of rail lines

The use of a ballastless track for high-speed operations enables a more direct routing of train lines, with tighter radii and greater slopes. These benefits enable the reduction, or even elimination, of the costs of and the work required on civil engineering structures. These benefits have led to the application of ballastless track technology in the major projects for rail lines currently being undertaken in Germany, where approximately 800 km of ballastless track has been installed since 1991, as well as in other major projects around the world. The ballastless track has found applications in many areas, as detailed in Table 32.3.

Table 32.3 Applications of ballastless tracks

Area of application

Remarks

Main lines

Suitable for axle loads of 15 to 35 t

Urban light rail

Low-vibration profile and good aesthetics, suited for use in intracity commuter lines

Tunnels and

Poor drainage and tamping difficulties are major problems with

underground tracks

respect to the conventional track. A ballastless track with a centre drain provides a low-maintenance, geometrically stable alternative.

Stations

The use of ballast results in continuously varying rail-to-platform heights. This is dangerous for passengers.

(contd)

Table 32.3 (contd)

Area of application

Remarks

Desert areas

Bridges and elevated structures

Fouling of the ballast due to wind-blown sand is a major problei in arid areas. Ballastless technology resolves this problem.

The omission of ballast allows for narrower and lighter structure than would be possible with a ballasted track. This has significa cost benefits.

Material handling and loading facilities

A ballastless track is suitable in situations where the loading of material such as coal and chemicals either contaminates the ballast or pollutes the sub-soil. A ballastless track may be backfilled to the rail level to allow unimpeded access across the track access for vehicles.

The Indian Railways does not have any plans for providing ballastless tracks for high-speed routes because the maximum permissible speed is only 140 km/h at present. However, ballastless tracks are provided in the case of underground railways due to other considerations. Figure 32.1 shows the cross section of a ballastless track for underground railways.

Fig. 32.1 Ballastless track for underground railways

Summary

Many countries in the world have developed a high-speed rail systems, with trains running at a speed of more than 200 km/h. A higher speed of 350 km/h or more is also possible if it is ensured that the track system is free from adhesion. The maximum speed that has been achieved so far on Indian Railways is 140 km/h. This limited speed is mainly due to the old track structure and the presence of old bridges. Track modernization and improved track maintenance methods will enable high speeds and smooth journeys on Indian Railways.

Review Questions

1. Write short notes on the track requirements for high-speed trains.

2. Enumerate all the important work which may have to be undertaken for strengthening and improving an existing track so that higher speeds are permissible on it.

3. What are the various measures normally taken to improve the track for it to accommodate high speeds?

4. Write short notes on ballastless track and movable crossings.

High-speed Ground Transportation System | RAILWAY ENGINEERING