The third longest railway tunnel in the country connecting the under-construction Vizhinjam International Seaport being developed by the Adani Port with the railway mainline at Balaramapuram near Thiruvananthapuram will use the New Austrian Tunnelling Method (NATM) for undertaking the tunnelling works. The work scheduled to begin in January will take 36 months for the completion of tunnelling work alone plus three months of initial installation work and another 3 months for track lining and commissioning, taking a total of 42 months for the entire work.
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The country’s largest 12.75 km long railway tunnel (T-49) is built as part of the Udhampur-Srinagar-Baramula Rail Link (USBRL) project, surpassing the 11.2-km long Pir Panjal Tunnel on the Banihal-Qazigund section. Instead of using the expensive tunnel boring machine (TBM), Vizhinjam International Seaport Limited (VISL) which is implementing the Vizhinjam deep water multipurpose seaport on a PPP basis, adopted the cost-effective NATM method which uses a modern drilling and blasting technique.
The cross-section profile of the single-line broad gauge railway tunnel is likely to be horseshoe-shaped. By using the NATM, the authorities are planning to do the tunnelling works in three or four phases simultaneously. Further, machines to be pressed in for tunnelling work can be reversed inside the tube at any point of time by adopting this method. In addition, the excavated boulders, and soils can also be re-used for construction purposes to a greater extent, said sources.
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The 9.02 km long tunnel with a depth of 25-30 meters below the ground is expected to not be a daunting task for the authorities as the examination of the soil strata reveals soft rock, weathered rock, and silt along the route. However, underground aquifers prone to flooding are likely as Vellayani Lake is close to the route. On completion, the rakes from the Vizhinajm port can pass through the tunnel in just 36 minutes with an average speed of 15-30 kmph.
The ₹1,120 crore-project requires 6.431 ha to connect the port with Balaramapuram halting station with a total length of 10.7 km. Balaramapuram halting station will be upgraded as a connecting station and the cost required for this would be borne by the VISL. The construction will be on Non-Governmental Railway (NGR) model that ensures private sector participation to provide last-mile connectivity. The State has recently given nod to sign an agreement with the Southern Railways for constructing the line under the NGR model.
The fund for the work will be sourced from the National Bank for Agriculture and Rural Development (NABARD). VISL had already entered an agreement with Konkan Railway Corporation Ltd, which is the implementing agency, in 2018. Though the Vizhinjam port had received Environmental Clearance, the State has given an application to amend it as the rail connectivity to the port was then conceived over the surface. In the wake of the change in the construction model, the State has now asked the Central Institute of Mining and Fuel Research, Dhanbad, to hold a study of the underground tunnel project and submit a report in one month.