Faced with a tricky terrain in the Himalayas, engineers of the Indian Railways have developed a new tunnelling method to complete the construction of Tunnel-1 on the 111-km-long Katra-Banihal section of the Kashmir rail link project. The 3.2-km-long single tube tunnel, located at the foot of the Trikuta Hills in the Katra-Reasi section of the Udhampur-Srinagar-Baramulla Rail Link Project, has been described as the most difficult section of the project."We have innovatively developed (I)-TM as Himalayan tunnelling method for tunnelling through the Himalayan geology to build tunnels in Jammu and Kashmir," Railway Minister Ashwini Vaishnaw had said recently.

Explaining the new tunnelling method, a senior railway engineer said it involved providing pre-excavation support measures to tackle the "flowing conditions" encountered while excavating the tunnel. The railways also changed the alignment of the rail line to ensure that only a small portion passes through the tricky terrain, which the engineers had described as the worst conditions ever encountered in building tunnels anywhere in the country.

A senior railway engineer, who has been involved in the construction of the project, said the engineers decided to provide rigid supports using 'ISHB' as against the lattice girder method used in the New Austrian Tunnelling Method.

"We inserted nine-metre pipes in the mountains. It is called pipe roofing. We made an umbrella using these perforated poles and filled them with PU grout. It is a chemical that mixes with the soil and increases its volume three times over and solidifies the soil like a rock. This structure is tested for stability and then we proceed with the excavation bit by bit," the engineer said. He said the engineers also designed stress release holes and wing drainage holes to allow the strata to relax and lose water. The difficult terrain has led to slowing down of the work.

"Had these conditions been encountered in any other country, they would have abandoned the site. But we decided to go ahead and employed a new tunnelling method," he said.

Work was held up on this crucial tunnel for over three years since 2017 and engineers now plan to complete it by early next year.

The 111-km-long Katra-Banihal section predominantly involves tunnelling. There are 27 main tunnels (97 km) and eight escape tunnels (67 km). The section has 37 bridges, of which 26 are major and 11 minor ones.