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Tuesday , 16 April 2024

Sela Tunnel Project: Overcoming the Impossible

Owing to the subduction phenomenon, tunnel construction in the Himalayan region is probably the most challenging construction activity in the field of civil engineering. Sela Tunnel Project is undeniably the most complex and difficult project being taken up in the nation today. Once completed the tunnel will offer the world the longest bi-lane tunnel at an altitude above 13,000ft; another world record for BRO.

Tawang is an important town in the North-East state of Arunachal Pradesh. Known for its world famous Tawang monastery, Tawang is also famous for its well enriched Buddhism and the Monpa Tribe in the region. Monpa is one of the oldest tribe of Arunachal Pradesh which follows the Lamaistic tradition of Mahayana Buddhism.

Balipara-Charduar-Tawang Road is the only road connecting the famous town with Tezpur and Guwahati. The road has a total length of 317.520km and connects important places like Tenga, Bomdila, Dirang, Jung in between the road traverses through breath taking valleys, natural lakes, snow clad mountains and the rivers and Nallahs. Being the hilly and treacherous turn, there exists numerous bottlenecks in the route. The major chokepoints on the route are fog hidden hill top of Nechiphu, heavy traffic prone town of Bomdilla and highest mountain pass on the route i.e. Sela Pass at an altitude of 13,700 feet.

Border Roads Organisation (BRO) is responsible for this road. The organization successfully circumvented the existing bottlenecks by constructing 500m long Nechiphu Tunnel and Bomdila Bypass. The 500m long state of the art Nechiphu Tunnel was constructed on 12 Sep 2023.

The Sela Pass is the highest pass on Balipara-Charduar-Tawang Road located at an altitude of 13,700 feet, Sela Pass is known for its beauty and prepossessing view. However, Sela is also known for its treacherous and inhospitable terrain.

To exploit the hydroelectric potential of Tawang region, NHPC proposed two mega projects Tawang I and Tawang II of a potential of 1400 MW. NHPC had planned to bypass the Sela Pass by constructing a tunnel under Sela Pass. Since Sela remains snowbound for about eight weeks, continuous snow clearance operations are carried out by BRO to keep the axis open being the highest pass on the axis. The tunnel was to be constructed in a strategically acceptable time frame to offer all weather connectivity to Tawang.

Through the DPR, BRO proposed two tunnels of 475m and 1790m length with approach roads length aggregating to 9.075km. The alignment remained below the snow line and allowed for all-weather passage of vehicles without major challenges of snow clearance. The alignment saves a distance of more than 8km and cuts down the travelling time by an hour while obviating the treacherous Sela Pass climb.

Foundation stone of Sela Tunnel was laid by Hon’ble Prime Minister Shri Narendra Modi on 09 Feb 2019 and on 15 Feb 2019 a contract under EPC mode for design and construction of Sela Tunnel Project was awarded to Patel Engineering for civil works.    

Salient Features of the Project

The Sela Group has been referred to as Pari Mountain gneiss and Pidi Formation. These are considered equivalent the central crystalline Western Himalayas, Kanchanjungha gneiss of Sikkim-Darjeeling and Thimpu Group of Bhutan Himalaya. Rocks of Sela Group are divided into Lower Taliha Formation and Upper Galensiniak formation based on difference in lithology.

The initial contract of the Sela Tunnel included two tunnels, viz 1790 m and 475 m long and 9.075 km approach road. The lengths of the tunnels and approach roads were subsequently changed based on site conditions and to overcome a few challenges.

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