The Rohtang tunnel, now popularly known as the Atal Tunnel, was inaugurated on October 3, 2020, after a wait of almost 10 years. Notably, it is the highest altitude tunnel in the world. It is the world’s longest motorable road at an altitude of over 3,000 metres. The project entailing construction of a strategic tunnel below the Rohtang pass was first conceptualised in June 2000.
The Rohtang tunnel was conceived with the aim of providing round-the-year connectivity in the Pir Panjal ranges of Himachal Pradesh, since the Manali-Sarchu-Leh road remains cl-osed for nearly six months in the year as a result of the Rohtang pass being completely snow covered. The 9.02 km long tunnel connects Manali to the Lahaul-Spiti valley and is at an altitude of about 3,000 metres (10,000 feet) from the mean sea level.
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 north portal is located near Teling village, Sissu, in Lahaul Valley at an altitude of 3,071 metres. The tunnel is horseshoe-shaped, with a single-tube double lane and a road of 8 metres. It has an overhead clearance of 5.525 metres and is 10.5 metres wide. It has a 3.6×2.25 metre fire-proof emergency egress tunnel built into the main tunnel itself. There are 18 egress tunnels; thus after every 500 metres there is an opening in case of an emergency.
The tunnel has been designed for a traffic density of 3,000 cars and 1,500 trucks per day with a maximum speed of 80 kmph. It has a state-of-the-art electromechanical system including a semi-transverse ventilation system.
The tunnel has a number of safety features built in, including telephone connections at 150 metre intervals for emergency communication, fire hydrant mechanisms every 60 metres, a turning cavern every 2.2 km, an auto incident detection system with CCTV cameras every 250 metres, air quality monitoring every 1 km, evacuation lighting/exit signs every 25 metres and a broadcasting system throughout the tunnel. Talking of the many firsts the tunnel boasts of, Satish Paretkar, director and head, hydro and underground business unit, Afcons says, “This is the first tunnel to deploy the Rowa flyer technology, which allowed engineers to work at inverted levels. It is also the country’s first tunnel to have an escape tunnel within the main tunnel. Generally, escape tunnels are built separately along the main tunnel. The tunnel is horseshoe-shaped, with single tube and two lanes. The drill and blast technique for excavation as part of the New Austrian Tunnelling Method has been used for its construction.” Further, the tunnel receives 4G network coverage which is a rare occurrence in tunnels in the country.
Brick by brick – The journey
Though the project was conceived in 1983 and announced by then prime minister Atal Bihari Vajpayee in June 2000, the project did not take off. On May 6, 2002, the Border Roads Organisation (BRO) was entrusted with the task of constructing the tunnel. In 2002, the foundation of the approach road to the tunnel was laid. The BRO subsequently engaged RITES Limited in the same year to undertake studies.
However, the work still did not progress much and the project had not moved beyond the tree-felling stage by May 2003. In May 2007, the contract for design and project management was awarded to Australia-based SMEC Holding Limited (formerly Snowy Mountains Engineering Corporation International Private Limited), and the completion date was revised to 2014. Despite multiple announcements that work on the tunnel would begin in 2008, no progress was made till November 2009.
The construction contract for the project was awarded to a joint venture of Afcons Infrastructure Limited and STRABAG AG, Austria in September 2009 after the Cabinet Committee on Security cleared the Rohtang tunnel project. Construction work commenced in 2010.
The first blast took place in 2010 and the final blast in 2017. The construction of the tunnel proved to be a monumental task with the project facing multiple delays.
Initially estimated to cost Rs 5 billion (2000), the project cost escalated to Rs 9.5 billion in 2005. The contract was awarded to Afcons and STRABAG at an escalated cost of Rs 14.58 billion. This cost escalated further and the project was eventually completed at a cost of Rs 32 billion-Rs 35 billion.
An uphill task indeed
Tunnel construction has always been fraught with challenges. The most formidable task in this case was to continue with the excavation work during heavy snowfall during the winter season. The Seri Nala fault zone, a 588 metre stretch from the south portal, was the most difficult challenge that the tunnelling team faced. “This zone surprised everyone with extremely fractured and pulverised rock. The rock mass consisted of decomposed rock fragments of phyllite, quartzitic phyllite, schist and riverbed materials with heavy water ingress. There were constant collapses with water ingress as high as 8,000 litres per minute. Tunnel heading became extremely challenging which even led to considerations such as changing of the tunnel alignment. This became a real test of patience and persistence. Almost after four years of toil, the Seri Nala fault zone was conquered,” says Paretkar.
Excavation for tunnelling was done from both ends. However, as the Rohtang pass closes during the winter, the north portal was not accessible during that time and excavation was carried out only from the south portal. Only about one-fourth of the entire tunnel was excavated from the north end, and the remaining three-fourths from the south end. “The tunnel is an outcome of over 1,000 workmen and 150 engineers working tirelessly and efficiently in extreme weather conditions. There was a constant avalanche threat with over 20 avalanche areas surrounding the tunnel portals. The tunnel has consumed 14,508 metric tonnes of steel and 237,596 metric tonnes of cement, and 1.4 million cubic metres of soil and rocks has been excavated,” says Paretkar. At its peak, the tunnel is 2.5 km deep in the mountain belly at the south portal side and the lowest overburden is 1.5 km.
The way forward
The tunnel has reduced the road distance between Manali and Leh by 46 km and the travel time by five hours. It will provide almost all-weather connectivity to Indian Army troops posted in Ladakh. The tunnel is also expected to help promote tourism in the region. Going forward, the tunnel will serve as a reference point for more such tunnels to be built in the region. As per reports, if complete all-weather connectivity is to be maintained, the Manali-Leh route will require the construction of another two to three tunnels.