The Atal Tunnel, which has been constructed at an altitude of 3,000m (10,000 ft) over sea level and opened by Prime Minister Narendra Modi in October 2020, has lately seen its excavation company delighted due to receiving the prestigious CII Industrial Innovation Award.
In order to honor its pioneering engineering solution at the world’s longest highway tunnel the Afcons Infrastructure Limited (Afcons) was given this award.
The iconic Atal Tunnel is an engineering marvel in the Himalayas. The 9.02km tunnel is a game-changer for Lahaul and Spiti district as it provides a safe, all-weather connectivity to the remote region with Manali, and eventually with the rest of India.
The encountered challenges in constructing this tunnel comprised of extreme weather and poor geological conditions, sorely fractured and pulverized rock at the South Portal near Dhundi, that caused a complete collapse of the tunnel face at the Seri Nala fault zone.
Moreover, rushing around 8,000 liters of water per minute into the tunnel as well as muck flooding of the dug area, led to significant speed down in tunneling progress that was from 120m monthly to about 20m per month, according to the company.
Reinforcing the damaged roof by a seamless array of long pipes (12-15m) to build an umbrella-like structure in the crown, was the ultimate solution of Afcons with a unique innovation in the form of pipe roofing system for this problem.
While most of the area was covered by a single row of pipe roofing, in extremely weak zones, double rows were created. Slow, yet steady, progress was made, and 40,000m of single and double pipe roofing was installed, it said in a statement.
According to Satish Paretkar, Director and BU Head, Hydro and Underground Works, Afcons: “The Atal Tunnel is an engineering marvel in its true sense. Never in India before a tunnel of this scale and complexity has been constructed. Although the Seri Nala fault zone was 526m, the excavation took four years to complete. Due to heavy water ingress, the face of the tunnel literally used to flow like a river of mud and boulders. Securing the tunnel face under these circumstances and excavating further was a huge task.”
Paretkar also added: “While overcoming the Seri Nala fault zone was daunting, this is one of the few tunnels in the world, and the first in India, that has been built with an emergency escape tunnel below the main tunnel. Passages have been provided at every 500m where a stairway leads to the escape route. In times of adversity, the escape tunnel can be used to evacuate people.”
Crossing the treacherous Rohtang Pass, the intended tunnel decreases travel time and ensures uninterrupted movement of people and supplies. Also, the habitants’ isolation during the six months of the winter will be halted by this new tunnel.