With an increase in the railway network across the country and the launch of new projects and trains, track and bridge infrastructure has come under increasing pressure. There is thus an urgent need to enhance inspection and monitoring techniques for railway tracks, and maintain and strengthen existing bridges.
Indian Infrastructure looks at the current techniques being deployed to maintain this infrastructure and the possible measures that can be taken in the future…
Track inspection and monitoring
The country’s railway network spans a track route of 118,000 km, having increased substantially over the past couple of decades. Given the immense scale, Indian Railways (IR) takes several measures to ensure adequate maintenance of its track network. This is done by daily inspection of the tracks and periodic visual inspection by using push or motor trolleys and point asset inspections.
IR deploys both manual and mechanised techniques for track monitoring. This is owing to limited technological solutions available for use at present. Therefore, track recording cars and push/motor trolleys are currently being used for such works. However, more mechanised techniques such as oscillation monitoring systems and ultrasonic track testing through ultrasonic flaw detection (USFD) machines are also in use. Digital single- and double-rail testers are both being used for track monitoring using USFD machines, which are also enabled with global positioning systems. More recently, IR has also adopted new technologies such as self-propelled ultrasonic rail testing cars for track monitoring works.
These technologies are used to undertake various types of track maintenance works, such as tamping (undertaken annually), overhauling (once every three-five years), deep-screening (once in 10 years), rail welding, etc.
As of September 2017, IR has a total of 835 track maintenance machines and the acquisition of another 547 is in the pipeline. Under the railways’ master plan for track improvement, the total number of machine holdings is envisioned to be increased to 2,705 by 2020 and 2,805 by 2024.
However, track maintenance comes with its own set of challenges. These include ensuring rail safety by maintaining not just the track network, but the entire ecosystem of rolling stock, signalling works, etc. Besides this, the authorities need to ensure safety of the rail-wheel interaction. Several societal issues such as track trespassing and theft also become hindrances in maintaining track conditions.
To overcome these issues and to increase efficiency in track management, several information technology (IT)-enabled tools have been deployed by IR. These tools help the railways in ensuring a single source of data at all levels for tracking inspections, work processes, information quality and real-time visibility, and undertaking performance monitoring. One such tool is the track management system, which helps in the online assessment of all asset inspections and material changes made on tracks. Another key system being used is the project management and information system. IR is planning to integrate this system with a geographic information system soon to enhance the quality of data collection.
Upgrading rail bridges
IR has a total of 140,919 rail bridges at present. Most of these are minor bridges (128,602). Meanwhile, there are 11,653 major bridges and 664 important bridges in the country. The age of most of these bridges is 60 to 80 years, while about one-fourth of the existing bridges were constructed over 100 years ago.
Given their age, IR has felt the need to upgrade these bridges to keep pace with technological developments in the railway sector. For instance, bridges need to be upgraded for running higher axle load trains such as 25 tonne axle load trains and high horsepower locomotives. For this, an assessment methodology for checking the design of existing bridges has been developed. Bridges on identified routes have also been checked for their capability of running higher axle loads at reduced speeds. Meanwhile, existing bridges have been rehabilitated and strengthened so as to equip them to carry such loads.
With an increase in axle loads, high-powered locomotives are required for hauling trains. These locomotives have higher tractive effort and braking force, causing greater longitudinal force on the bridges. Therefore, IR is considering permitting higher longitudinal forces on substructures of bridges through the modification of bearings and the provision of shock transmission units or similar suitable technology.
With the launch of high speed rail projects, IR has taken up works to study the coefficient of dynamic augment (CDA) of steel bridges for speeds of more than 160 km per hour. However, further work is required to study the CDA for concrete bridges as well.
Further, to enhance the reliability of IR’s bridge assets, new codes for seismic design of bridges are being prepared in line with international codes, a new formula for scour estimation is being finalised, a continuous monitoring system of scour measurement is being developed, and a painting technology with a longer life for steel girders is being deployed as well. At the same time, a railway bridge health monitoring system with wireless sensors for remote/continuous monitoring of bridge parameters is under development.
However, further work is required to increase the use of non-destructive testing and instrumentation of bridges, especially for residual life prediction. At the same time, better coatings and repair materials for concrete bridges and reinforcement bars need to be explored, and lightweight CC cribs and reduced height girders need to be developed.
Meanwhile, new techniques and technologies need to be adopted in the railway sector. These include completely welded girders, long-life coatings for steel and concrete bridges, fibre-reinforced plastics as repair materials, spherical bearings/shock transmission units, and external prestressing techniques for strengthening of bridge members.
Thus, the railway network in the country, specifically tracks and bridges, is in need of constant monitoring and upgradation. IR has initiated the adoption of various technologies for undertaking these works. However, a significant shortfall remains in improving the track and bridge infrastructure. Investments in these works are thus expected to increase in the near future.
Based on presentations by A.K. Singhal, executive director, bridges and structures, Railway Board, and B.P. Awasthi, executive director, track, Indian Railways, at a recent India Infrastructure conference