The company that excavated the Atal Tunnel, constructed at an altitude of 3,000m (10,000 ft) above sea level near here and inaugurated by Prime Minister Narendra Modi in October 2020, has recently been conferred the prestigious CII Industrial Innovation Award.
Afcons Infrastructure Limited (Afcons) was given the award for its pioneering engineering solution at the world’s longest highway tunnel.
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.
Constructing this tunnel was nothing short of a roller-coaster ride. Excavation was extremely challenging due to extreme weather and poor geological conditions. At the South Portal, near Dhundi, extremely fractured and pulverised rock led to complete collapse of the tunnel face at the Seri Nala fault zone.
Almost 8,000 litres of water per minute gushed into the tunnel along with muck flooding the excavated area. This slowed down tunnelling progress from 120m per month to almost 20m per month, the company said in a statement.
The problem was finally solved by Afcons with a unique innovation in the form of pipe roofing system. The heavily damaged roof was strengthened using a seamless array of long pipes (12-15m) to build an umbrella-like structure in the crown.
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.
“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 of 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,” said Satish Paretkar, Director and BU Head, Hydro and Underground Works, Afcons.
“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,” Paretkar added.
The tunnel bypasses the treacherous Rohtang Pass, reduces travel time and ensures uninterrupted movement of people and supplies. It also opens a new chapter in the lives of locals at Lahaul and Spiti by ending their six-month isolation during winter months.