One of the key issues faced by Indian Railways (IR) pertains to the design and maintenance of tracks with continuous pressure for enhancement of the line-carrying capacity. This issue can only be mitigated by enhancing the permanent way (P-way) carrying capacity along with maintaining the desired level of safety and reliability at the minimum cost. While opting for capacity enhancement, structuring of the railway track plays a pivotal role. However, this and several other factors are often ignored while planning for railway capacity augmentation, leading to an increasing number of rail fractures and accidents. But, with the alarming number of rail accidents reported in recent years, IR is paying greater attention to the detailed examination of track structures and other safety parameters.
Factors affecting track structures
To enhance IR’s carrying capacity, it is important to examine and understand the factors that affect track structures. The most important element in track structuring is the rail. The structuring of the track can be undertaken depending upon the cross-sectional area and the shape of the P-way, which is one of the key elements of a rail track. Another critical factor is the metallurgy of the rail structure, which further depends on the type of rolling stock being operated on the track.
Other key factors that play a major role in deciding the rail structure includes the temperature gradient, rail metallurgy grades (such as heat-treated grade or head-hardened grade) and key maintenance practices such as rail handling, rail grinding discipline, rail operation culture, rolling stock design and maintenance culture, wheel load, etc. Monitoring of the temperature gradient is especially important while structuring the railway tracks to avoid rail fractures due to differential temperatures.
Further, stresses on the track due to the various kinds of forces applied on it adversely affect the capacity of railway tracks. These include the bending stress (caused due to the wheel load on railway lines), longitudinal stress (caused by temperature variations on railway tracks), yield capacity stress and residual stress in rails (occurs during the manufacturing, straightening and cooling of the rails). These factors along with the loading/unloading and rail maintenance culture, and rolling stock design should be considered while calculating capacity enhancement requirements for different railway sections.
Fastening systems and sleepers: Requirements and new innovations
Fastening systems are categorised into different codes and norms on the basis of corridors, ranges, axle load and type of tracks. Typically, IR procures special types of fastening systems that serve a particular type of railway corridor. For instance, corridors with higher speed, noise and vibration levels require a fastening system that is equipped with high resilience slab systems. On the other hand, corridors with heavy axle loads require fastening systems with secondary stiffness to avoid rail fracture during operations. UK-based Pandrol Track Systems and Germany-based Vossloh AG are IR’s main suppliers that provide a wide variety of fastening systems as per the specific requirements.
In 2015, IR developed a new variety of sleepers that are heavier in nature and provide higher frame resistance with an increased rubber pad size to enable load distribution over a larger area, thereby reducing the chances of rail fractures. Over the past two-three years, a number of modifications have been introduced in this new sleeper design. These pertain to an increase in the weight from 270 kg to 350 kg and the top diameter to 250 mm.
Conclusion
Even though there are various issues delaying capacity augmentation of existing railway tracks, there are several ways to achieve this in an effective manner. These include conversion of longer block rail sections into shorter sections (on absolute block systems) by introducing immediate block huts, undertaking continuous track circuiting, introducing moving train block systems with a headway of four-five minutes, reducing differential speeds of freight and passenger operations on corridors where both goods and passenger trains are operated simultaneously, reducing wagon axle loads and improving suspensions.
Overall, there is an urgent need to select the best available technology for track construction. Measures need to be taken to identify the actual forces causing rail fractures and develop a dedicated maintenance regimen for the existing rail infrastructure. To meet the long-term goals that have been set for track capacity enhancement and speed upgradation, it is important to select the appropriate metallurgy structure and give due attention to identifying various types of stresses on the track, thereby ensuring a better outcome.
Based on a presentation by Vipul Kumar, Executive Director, Track, Railway Board, at a recent India Infrastructure conference