Atal Rohtang Tunnel- Tale of Extreme Challenges | an inside perspective

Prime Minister Narendra Modi will inaugurate 9.02 Km Atal Rohtang Tunnel to the nation on 3rd October 2020. This tunnel holds the distinction of being the “World’s Longest Tunnel above an altitude of 3000m”. It’s a moment of pride for me along with all other engineers, staff and workers of Afcons and Strabag AG and other stakeholders who were associated with this project.

It’s rare and once in a lifetime kind of an opportunity for a construction professional like me, to work in a project like Rohtang Tunnel. Beyond the colossal Strategic importance and Socio-economic benefits, the project had offered an insurmountable amount of challenges. Whether be it climatic, engineering or geological, there was no dearth of problems. Behind the engineering excellence, it was the true human grit, resilience and perseverance of the project team that made this Tunnel Project a success that we know of today. Any number of words would be insufficient to portray the problems and challenges conquered by the Project Team. This is an attempt to pen down a small glimpse of the challenges encountered during the construction phase of the Tunnel.

What makes the Rohtang Tunnel exceptional, is its structural uniqueness. It’s the only tunnel in India to have the emergency exit tunnel (EET) below the main carriageway. In most tunnels, emergency exit tunnels if provided, are constructed separately and in parallel to main tunnel. Construction of such structure requires comparably more time as progression of almost all activities falls in critical path.

The maximum overburden is almost 2 Km over Tunnel Alignment. This caused the temperatures inside tunnel at heading zone to rise as high as 42°C. Further, the lack of an intermediate ventilation Shaft caused frequent accumulation of fumes adding to the difficulty in working conditions. Complete revamping of Ventilation system was executed with advanced technologies to mitigate such suffocating situations. In the final phase of heading excavation, the situation was so worse that the workers would work only wearing their undergarment along with PPE. It was purely the zeal of such motivated workers and site engineers which culminated in the successful breakthrough on 15th October 2017. Mrs. Nirmala Sitharaman, the Defense Minister visited the site and graced the incredible Achievement of Tunnel Breakthrough.

Uncertainty in a Tunnel Project is highest among all the infrastructure projects. Further, the ever changing geological conditions aggravated the complications during excavation. One such stretch of 588 m was encountered just when it seemed like things were under control. Extremely poor geology in this 588 m stretch compounded with heavy ingress of water (127 Liter per Sec) had jeopardized the completion of the project. The implication of such adverse geology was so drastic that successful completion of the project became doubtful. Excavation Advancement Rate plummeted to 4m/month from 120m/month. After implementing all available technologies and methodologies the stretch was slowly, steadily but surely was excavated. It took 4 years to excavate the stretch of 588m, while it took less than 3 years to excavate 4281 m from South End of the tunnel.

Extreme climatic conditions became a new normal for the project team. Harsh winters where temperatures dipped to -27°C compounded with the risk of frequent Avalanches posed a major threat to life and material. One has to navigate through 13 Avalanche Zones between Solang Valley and South Portal of the tunnel, where the Project office was established. Primarily a team of highly trained rescue squad was deployed round the clock. Every personnel were mandated to carry a “Recco Chip”. In case of an emergency situation where one is caught in an avalanche, rescue squad could pin point the location along with the depth and can be rescued in time. Cloud bursts and flash floods were common during the monsoons. Avalanches in the winter and landslides during the monsoons put forth an unimaginable logistical challenges.

The completion of the project is a testament of human ingenuity and professional excellence that culminated in this engineering marvel in the Himalayas. The lessons learned and knowledge gained during the construction of this tunnel is unparalleled. The rich experience is an invaluable treasure not only for the country but also the engineering fraternity across the world.