Ballast-less Tracks by L&T: State-of-the-Art and its Future Prospects

The Railway Business Group (RBG) of L&T Construction Limited is a decade-old strategic business segment under the Transportation Infrastructure IC
ballast-less

Ballast-less Tracks by L&T: State-of-the-Art and its Future Prospects

The Railway Business Group (RBG) of L&T Construction Limited is a decade-old strategic business segment under the Transportation Infrastructure IC, which mainly deals with infrastructure projects in areas such as:

  • Mainline Railway
  • Metros
  • Light Rail Transit (LRT) Systems
  • High-Speed Rail Networks
  • System Integration

As a key Engineering, Procurement and Construction (EPC) player, RBG has been playing a vital role in developing Rail Infrastructure across India and internationally.

chart
Figure 1: Track Projects by L&T
RBG has strong design and construction capabilities in delivering Ballasted and Ballast-less Projects, with the former being used mainly in freight corridors and main lines, and the latter being used majorly in Urban Mass Transit Projects. Since its development stage in various countries and specific fields of application, the ballast-less track technology, with a bearing structure made of concrete instead of ballast, has experienced tremendous innovation and has become a serious alternative to traditional ballasted tracks. In High-Speed Rail and Urban Transit operations, this has gained predominance. For these applications, the specific features of a rigid bearing structure, combined with elastic components, have proved to be the most favoured technical choice of respective authorities, decision-makers and industry experts.

Railways in India and the Use of Ballast-less Tracks

The Indian railways – the second largest rail network (under one management) worldwide – is under operation and plays a dominant role in passenger and freight transportation in the country. However, the national rail transport infrastructure still faces challenges. Hence, the structural improvement of rail infrastructure, targeting high availability and low maintenance, is of great importance.

With this scenario in mind, India has made huge investments in the following domains:

  1. New Urban Transport systems in various big cities, and expansion of already existing MRT (Mass Rapid Transit) systems,
  2. Expansion of freight transport capacity by new Dedicated Freight Corridors (DFC),
  3. High-speed and semi-high-speed corridors on major routes across the country.

For the first and third domains mentioned above, the applications of ballast-less tracks have gained strong momentum and further enhancement of markets is expected in the future. For the second, ballasted tracks remain a preferred choice.

Types of Ballast-less Tracks in India by RBG

1. Plinth Track
The plinth track system is typically used in urban metro rail systems, where tracks are placed on bridges. It offers accessibility for maintenance and integration with stations, and enhances the aesthetics and safety of the metro corridors. Urban metros largely prefer elevated sections since:
  1. It minimises disruption to existing infrastructures (the elevated tracks bypass obstacles such as water bodies, roads and transportation networks).
  2. Extensive modifications to the urban landscape are reduced, resulting in fewer disruptions during construction.
  3. Compared to the Underground sections, elevated sections are cost-effective and faster to construct.
  4. Offer flexibility in route planning and alignment, allowing adaptation to the urban environment and efficient utilization of available space.
  5. Seamless Integration with metro stations.
  6. Lower land acquisition requirement.
Plinth tracks help minimise noise and vibration generated by train operations, making them suitable for urban areas where noise pollution is a concern. The elevated structure contributes to a quieter environment. The plinth track system is used by L&T in metro rail projects in cities like Delhi, Mumbai, Chennai, Hyderabad and Bengaluru in India and Riyadh Metro.
Plinth Track in Mauritius LRT
Figure 2: Plinth Track in Mauritius LRT
Plinth Track in Ahmedabad Metro
Figure 3: Plinth Track in Ahmedabad Metro

Like the track structure on elevated sections, the track structure in Underground corridors is a cast-in-situ slab track. It is important to note that most Underground sections in urban areas now require Vibration isolation featured in the slab track, popularly known as the Mass Spring System (MSS).

An elastomeric layer is placed below the slab track Structure, such that the vibrations in the Track Slab are isolated from the substructure. The goal of vibration isolation is to dynamically decouple the superstructure from its environment to reduce the transmission of vibrations and structure-borne noise.

track cross section
Figure 4: Track Cross Section with MSS
Strip bearing

2. LVT Booted Block Track System

This system is one of the first slab track systems in the world and has evolved from bi-block ties for ballasted track to the booted single-block system low vibration track (LVT) in use today.

The LVT supports consist of a concrete block with an elastic pad encased in a rubber boot and surrounded by cast-in-situ concrete. The elastic components of the system are designed on a project-specific basis and provide the characteristic properties of dual-level elasticity. Thus, influences in the low-frequency range, as well as in the higher frequency range, are reduced to a minimum. The rubber boot separates the concrete block of the LVT support from the surrounding concrete, which reduces vibrations and at the same time enables the components to be replaced quickly.

Due to its flexibility LVT Booted Block system is superb for several different applications including tunnels, open track, bridges, high-speed lines, metro projects and heavy goods traffic.

Due to its flexibility LVT Booted Block System is superb for several different applications including tunnels, open tracks, bridges, high-speed lines, metro projects and heavy goods traffic.

For the first time in India, this system is being installed by L&T in Mumbai Metro Line 3 connecting Colaba-Bandra-SEEPZ by an underground stretch that is 33.5 RKm (Route Kilometre) long.

Figure 5: Components of LVT Track System
Figure 5: Components of LVT Track System
Figure 6: LVT Track in Mumbai Metro
Figure 6: LVT Track in Mumbai Metro

3. Embedded Track

The Embedded Track system utilised by L&T involves embedding the tracks within the concrete slab. It is a highly advanced and innovative approach to railway track construction. The Embedded Track system also allows for faster construction and minimizes disruptions during installation and maintenance activities. Overall, it provides a modern and durable track infrastructure for metro networks.

In this system, a concrete slab is cast on the formation level, and the rails are embedded within the slab during the construction process. The rails are encased in encapsulation elements that act as a fastening system and provide electrical as well as vibration isolation along with better rail stability. The space between the rails is also filled with concrete, forming a solid and continuous track structure.

track
Figure 7: Encapsulation in Embedded Track

One of the primary advantages of the Embedded Track system is its ability to provide enhanced performance and durability. Embedded track technology has been used in several metro projects by L&T, majorly in Mauritius LRT.

Figure 8: Embedded Track with Concrete Finish
Figure 8: Embedded Track with Concrete Finish
Figure 9: Embedded Track with Grass Finish
Figure 9: Embedded Track with Grass Finish
4. PORR Slab Track

Being a proven and maintenance-free system, it enhances quality and faster execution with precise tolerances and is suited for high-speed/semi-high-speed operations. PORR slab track technology was selected by the National Capital Region Transport Corporation (NCRTC) for implementation in India’s first semi-high-speed project (Delhi -Meerut corridor) being executed by RBG.
 
The Delhi-Meerut project is the first PORR Slab Track implementation in India which is planned with a design speed of 180 Kmph.
 
The PORR precast slab track system is a state-of-the-art technology which consists of the precast slab with an elastomeric layer at the bottom (which enables quick & easy repair) and it is grouted and fixed on a thin base layer constructed from self-compacting concrete (schematic below).
Figure 10: Components of PORR Track System
Figure 10: Components of PORR Track System
Figure 11: PORR Slab Track in RRTS
Figure 11: PORR Slab Track in RRTS
This precast slab track system provides several advantages, such as long service life (estimated service life of 60 years), faster execution, precise tolerances, quick repairs, etc.

Owing to the successful implementation of the system in the Regional Rapid Transit System (RRTS) project and easy maintenance concepts, the PORR slab track system is envisaged to be the preferred system in other upcoming projects as well.

5. Shinkansen Slab Track/J Slab

India’s first highspeed project i.e. the Mumbai-Ahmedabad High-Speed Rail project is being constructed with the Shinkansen slab track technology. The project is designed for a maximum speed of 350 kmph. Slab Track structure is a unique feature of the Japanese High-Speed Railway, popularly known as the Shinkansen.

Slab Track consists of a precast Reinforced Concrete (RC) slab, over which fastening devices and rails are fitted. Over the roadbed concrete, either on the viaduct or in a tunnel, track bed concrete of about 300 mm and circular concrete dowel/anchors of diameter 520 mm and height 250 mm are cast at regular intervals of approximately 5 meters. Over the track bed concrete, the track slab is laid and a gap of about ~50 mm is created between them which is filled by pouring Cement Asphalt mortar in specially designed synthetic bags. The Concrete Anchors prevent the Slab Track from moving either in the longitudinal or transverse direction. The RC slabs for Slab Tracks are produced in designated factories.
Figure 12: Components of Shinkansen Slab Track
Figure 12: Components of Shinkansen Slab Track

Market Outlook

The railway network across the world is expanding and in India, the National Rail Plan 2030 has outlined the expansion of the existing rail network by 2031. This includes new Freight corridors (3,278km), High-Speed Corridors (2,521km) and Metros in all major cities.

Figure 13: Upcoming High Speed Rail Projects
Figure 13: Upcoming High Speed Rail Projects

The pace at which RBG has grown in the segment of ballast-less tracks is unsurpassable. With a promising market in the future, it is expected that the credentials developed by RBG will be valuable and will continue to make L&T a preferred partner for all types of ballast-less track projects.

Many more slab track technologies are being explored by L&T engineers and we hope to deliver iconic projects with them all.

Akshay Wahal
Akshay Wahal

Author

Author Bio

Akshay Wahal holds a B.Tech. degree in Civil Engineering and specialises in MEP from IIMA. With over 14 years of experience, he has dedicated a decade to L&T, showcasing expertise in ballast-less track design, project coordination between design and construction teams.

Author Bio

Nikhil Jose, a Civil Engineering graduate with a B.Tech. degree, brings over 10 years of experience to the table, all of which have been spent at L&T. His proficiency lies in ballast-less track design and track alignment design, making him a valuable contributor to the field of civil engineering.

nikhil jose
Nikhil Jose

Author

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