Sela Tunnel – An Engineering marvel at 13700 feet

Inaugurated by Hon’ble Prime Minister Narendra Modi in March 2024, Arunachal Pradesh’s Sela Tunnel is the world’s largest bi-lane tunnel. It will usher in a new era of economic prosperity for the Tawang region, fostering trade, tourism, employment and overall development.

Constructed at an altitude of 13000 feet on the Balipara-Charduar-Tawang road connecting Tezpur to Tawang in Arunachal Pradesh, Sela Tunnel is the highest in the country providing access to the hinterland up to Tezpur. It bypasses the treacherous Sela Pass at an altitude of 13700 feet. The road had numerous bottlenecks like Nichephu, Bomdila town and the namesake Pass, which have been addressed by Border Roads Organisation (BRO) by the construction of the Sela and Nichephu tunnels and Bomdila bypass.

The tunnel has been designed for a traffic density of 3000 cars and 2000 trucks per day with a max speed of 80km/hr. It will ensure all-weather connectivity to Tawang and forward areas. It will not only facilitate smoother movement of troops and supplies but also reinforce India’s defence capabilities in the region.

Sela tunnel was completed in March 2024, in just five years after overcoming challenges of difficult terrain and adverse weather conditions. The system consists of two tunnels of lengths 1003m and 1595m respectively with 8.6Km approach and link roads. The second tunnel also has an escape tube adjacent to the main tunnel as per international norms. The escape tube constructed parallel to the main tube is connected with cross passages every 500m. In case of emergency, this escape tube can be used for movement of rescue vehicles and evacuation of stranded people.

The tunnel has been constructed using New Austrian Tunnelling Method (NATM) which is widely accepted and used worldwide especially for Himalayan geology. It is based on the philosophy “Build As You Go” and involves using the inherent strength of the surrounding rock mass to support the tunnel. The execution of this mega project took over 90 Lakh man-hours with an average of around 650 personnel and labours working every day for the last five years.

The enormity of the tunnel making task could be judged by the use of 71,000 metric tons of cement, 5000 metric tons of steel and 800 metric tons of explosive for construction. A total of 162 plants and machinery were also dedicated to the making of the tunnel.

Various challenges were faced by Project Vartak of BRO during the construction phase. These included freezing temperatures up to -10°C and formation of icicles within, which caused delay in the concreting process. Ingress of water, cavity formation and restrictions due to COVID also affected the construction of the tunnel. Due to the cloud burst that occurred in July 2023, resources had to be augmented for reconstruction of damaged assets. Of the five years it took to complete the project, approximately 762 days had high snowfall or rainfall and 832 days had temperatures below 0°C, creating immense challenges for the personnel executing the work.

However, BRO was able to complete the tunnel in under five years due to the efficient use of technology, ground experience of executives and the hard work of civilian labour involved in the construction. The Sela Tunnel Project has been constructed with the highest quality standards with a well-prepared Quality Assurance Plan, as per IRC SP 91 and MoRTH Guidelines. The tunnel has state-of-the-art safety features including a ventilation system to maintain air quality, fire-fighting devices, CIE norms-based illumination system and SCADA controlled monitoring systems.

Sela Tunnel will bring in overall development of the region. Earlier the route to Sela Pass had only single lane connectivity and treacherous bends due to which heavy vehicles, container trucks and trailers could not get to Tawang. Due to adverse weather conditions, specifically in winters, evacuation of patients was adversely affected along the existing pass. The completed tunnel system will reduce the travel distance by more than eight km and travel time by an hour and will improve the quality of life of the people living in the region by providing easier access to healthcare, education and essential services.