Manali: Prime Minister Narendra Modi last week inaugurated the Atal Tunnel beneath the Rohtang Pass in Himachal Pradesh’s Kullu district to give a fresh boost to India’s border infrastructure.
“It is an example of world-class border connectivity,” Modi said after dedicating the highway tunnel, one of the world’s most challenging marvel of engineering motorways in the Himalayas, to the nation.
It will provide connectivity from Manali to the Lahaul-Spiti valley in Himachal Pradesh.
Modi said the work gained unprecedented momentum after 2014 and was inaugurated about two years ago on the occasion of Atalji’s birthday.
Modi interacted with Border Roads Organization Director-General Lt Gen Harpal Singh, who explained to him through a photo exhibition, about the hurdles the agency faced during the tunnel excavation. Singh explained how taming the glacial-fed Seri rivulet inside the tunnel was one of the biggest challenges for the engineers.
It’s a tributary of the Beas river and the tunnel alignment is beneath the rivulet.
The 9.02 km-long horseshoe-shaped single-tube, two-lane tunnel — the world’s longest motorable tunnel at over 3,000 metres above the sea level, is under the 3,978 metre Rohtang Pass in the Pir Panjal range.
“The all-weather tunnel can take any military traffic, even armoured vehicles,” a BRO official said.
Tunnel project Director Colonel Parikshit Mehra said the tunnel has manoeuvred one of the largest shear zones in the history of highway tunnelling. “A length of 587 m across the Seri-nullah or rivulet zone took us four years and the balance 8.4 km took almost the same time.”
Colonel Mehra said during excavation the temperature inside the tunnel rose to 55 degrees Celsius before the breakthrough and it hardly crossed 20 degrees after that.
On its vulnerability, he said, “The deep tunnels, in general, are not vulnerable to the tectonic effects since they move as a rigid body with shock waves.
With a maximum speed limit of 80 km per hour, the tunnel is expected to see traffic of 3,000 cars and 1,500 trucks a day.
The tunnel has consumed 12,252 metric tons of steel, 1,69,426 metric tons cement and 1,01,336 metric tons of concrete, and excavated out 5,05,264 metric tons of soil and rocks.
The construction contract of the tunnel was awarded to Strabag-Afcons, a venture between India-based Afcons Infrastructure and Austria’s Strabag.
Chandigarh-based SASE designed mechanical structures to ensure the safety of motorists by countering avalanches on both ends of the tunnel that remain under snow even during peak summer.
Engineers of SASE, a Defence Research and Development Organisation (DRDO) laboratory, said self-escape snow galleries have been erected for the safety of motorists after studying the local dynamics of avalanches like force and velocity.
The completion of the Atal tunnel is a key element in the Defence Ministry’s attempts to make the entire 475 km-long Manali-Keylong-Leh highway, used by the armed forces to reach forward areas in Ladakh bordering China and Pakistan.
The south portal of the tunnel is located at a distance of 25 km from Manali at an altitude of 3,060 metres, while the tunnel’s north portal is located near Teling village in Sissu in the Lahaul Valley at an altitude of 3,071 metres.
The double lane tunnel with a roadway of eight metres has an overhead clearance of 5.525 metres. It is 10.5-metre wide and has a 3.6 x 2.25 metres fireproof emergency egress tunnel built into the main tunnel itself.
Key safety features include the telephone connections at every 150 metres for emergency communication, fire hydrant mechanisms at every 60 metres, auto incident detection system with CCTV cameras at every 250 metres and air quality monitoring at every one km.