India’s longest under-construction rail tunnel nearing completion

Indian Railwayrsquos longest tunnel that is under construction is now nearing completion Named T49 the tunnel is the longest railway tunnel in the country and the Afcons constructed 732 KM nearly 6037 of the total tunnel It is linking the countryrsquos northernmost part ie the Jammu and Kashmir JampK with the rest of IndiaTo do so it is constructing a series of tunnels and bridges to navigate the rugged mountain terrain of the Lower Himalayas or Lesser Himalayas Punching through the mighty Peer Panjal ranges in the Lower Himalayas in JampK the railways are finishing the longest railway tunnel in India The UdhampurSrinagarBaramulla Rail Link USBRL project undertakes this arduous mission to join JampK with the mainlandThe T49 tunnel is 1275 KM long and connects the Sumber and Arpinchala Stations in the Ramban district of JampK Afcons has constructed 732 KM of the total tunnel which is nearly sixty per cent of the entire tunnel length Besides the main tunnel Afcons has also constructed two adits twenty cross passages two bridges and a station yard among othersDefying GravityTunnelling itself is a veritable challenge in the Himalayas Imagine the levels of complexity when constructing a tunnel with a downward gradient The gradient of a tunnel is a measure of how steep a slope or a line is It plays a major role in overall engineering amp construction Afcons constructed 732 KM of the tunnel from the north portal Arpinchala Village which is at an altitude of 1600MAlso Read Why do our trains have to wait for Vande Bharat Express CommutersAs a result one of the major challenges was the pouring of overt gantry concrete from an upward gradient to a downward gradient ldquoThe pouring rate of overt gantry concrete should not be more than 58 cumhr If the pouring rate is increased then there are chances of bulging of the gantry which will lead to misalignment To avoid this the team effectively and meticulously ensured an accurate pouring rate and the gantry mechanism was minutely surveyedrdquo said Chandra Shekhar Dixit Afconsrsquo Project ManagerExcavation ChallengesBesides the unique challenge of gravity there were few other known challenges in the region and especially in the context of constructing such a long tunnel Arranging ventilation systems dewatering and navigating adverse geological and climatic conditions were clear and present dangers In one of the tunnel sections a 450Mlong stretch had a thick overburden of 800850M ldquoThe overburden was causing incidents of rock bursting spalling and popping during excavation We drilled pressure relief holes to release the accumulated stress and installed Swellex bolts to provide immediate support Dixit saidIn another twokilometre stretch of the main tunnel there was a risk of high deformation due to squeezing ground conditions ldquoWe were facing a daunting challenge of diameter reduction by almost 115M This would have significantly impacted the project progress To avoid this we identified the stretch and reprofiled it the Project Manager explainedThere were other geological challenges like cavity formation due to the presence of a shear zone in the escape tunnel The construction activities were also impacted by huge water ingress ldquoThe dewatering system for more than 4 KMlong tunnel in a downward gradient was extremely challenging The increase in the length of the tunnel meant more water inside Dewatering arrangements for such a long tunnel having a head of 40M was dauntingrdquo Dixit saidDespite numerous challenges the breakthrough of the tunnel was achieved in February this year and thanks to the incredible efforts of Afconians and other engineers T49 will very soon be a matter of pride for the nation and the Indian RailwaysT49 Highlightsbull T49 is the longest railway tunnel in the countrybull The tunnel is 1275 KM long and surpasses the Peer Panjal Tunnel 112 KMbull It is part of the USBRL projectbull Breakthrough of the tunnel was achieved on Feb 15 2022bull Afcons has constructed 732KM nearly 6037 of the total tunnelbull Afcons has constructed the tunnel from the north portal which is at an altitude of 1600M