In 1983, the Government of India first visualized connecting the western Himalayan region of Manali to Leh in Ladakh, with an all-weather route. The existing connection via the Rohtang Pass used to be closed from November to May due to severe weather conditions. Although the project was given the go ahead by the PM in 1987 and RITES appointed to do the Feasibility Study in 1990, construction could only begin in 2010; the Atal Tunnel, a major link on the new all-weather Manali-Leh route, was completed in 2020. The tunnel is located at a mind-boggling altitude of 10,000 ft above mean sea level, an engineering marvel that can be counted amongst the world’s highest trafficable passes. Reducing travel time by four hours and distance by 45 km, the Atal Tunnel provides better connectivity for approximately 20,000 locals and enables seamless transport of military supplies/personnel throughout the year. The all-weather tunnel was opened to the public on October 3, 2020 by the Hon’ble Prime Minister of India, Shri Narendra Modi.
Go-ahead by the Prime Minister for the idea
Appointment of RITES for the Feasibility Study
*(RITES engaged M/s Geoconsult (an Austrian consultancy firm) for Detailed Project Report (DPR) preparation)
Feasibility Report – Phase I
Feasibility Report – Phase II
RITES suggested a tunnel along Manali-Sarchu-Leh route
RITES to prepare DPR
RITES submitted the DPR
Appointment of SMEC Holdings Ltd for design, engineering and advisory services
Contract awarded to Strabag-Afcons JV
Tunnel excavation work started
Excavation work completed
The Atal Tunnel is characterized by some unique and marvelous aspects, namely longest high-altitude tunnel, varying geology, tectonic thrust, excessive snowfall, high overburden, no adits and shafts, limited attack point options, exceptionally large cross-sectional area, heavy-duty ventilation fans, high stresses, varying working temperatures, rock spalling (bursting), heat tracing units, and electrical systems for high altitude.
The Atal Tunnel is a 9.02 km two-lane and single tube horseshoe-shaped tunnel, which links Lahaul valley in the extreme north of India to Manali valley in the southern part of the Himalayas, providing all-year connectivity. The 10m wide road in the tunnel has a 1m footpath on both sides and an overhead clearance of 5.525 m. The construction work on the tunnel began in 2010 using the drill and blast technique and New Austrian Tunneling Method (NATM) approach, instead of using Tunnel Boring Machines (TBMs).
The stakeholders opted not to use TBM because of machine jamming in the high deformations and pressures. Also, transporting heavy machinery on tight hairpin bends and Himalayan bridges was often dangerous and risky. After a period of seven years, in October 2017, the final breakthrough connection between the teams of the northern and southern portals was established. This breakthrough eventually made the accessibility of manpower and material easier from the south to the north, as the southern portal was less affected by adverse weather/climatic conditions.
Designed to hold a traffic density per day of nearly 3,000 cars and 1,500 trucks, the tunnel is equipped with a Semi Transverse Ventilation System, Supervisory Controlled and Data Acquisition (SCADA) controlled illumination, and firefighting and monitoring systems. The need to construct a new tunnel primarily resulted from the severe winters and heavy snowfall (average 24 ft), that would often lead to the closing of Rohtang Pass for more than six months. The tunnel region, in the years 1862, 1886, and 2014, recorded unpredictable snowstorms and avalanches. Additionally, there were often several casualties on the Rohtang Pass route. Limited connectivity for the locals in Leh and the region’s strategic importance due to its proximity with the international boundary, also created the necessity for an all-weather route.
The design challenges associated with the tunnel works were unique due to the geotechnical conditions in the Pir Panjal range of the Himalayas. The design element had to take into consideration adverse climatic conditions, seismic zone, adequate ventilation, and structural strength at such a high altitude.
The construction stage witnessed massive natural and man-made challenges like the disposing of 800,000 cubic meters of excavated material, constant de-watering efforts, and unstable rocks, which slowed the blasting and digging activities. During the construction stage, difficulties were predominantly experienced in the tunnel excavation activity. Due to heavy snowfall, the excavation activity from the northern portal was not accessible, which only paved the way for the task from the southern end. There were nearly 46 avalanche sites on both the north and south end of the tunnel. Another hurdle was encountered during excavation from the south portal, wherein 8,000 liters of water, along with muck, gushed into the tunnel from the Seri Nala Fault Zone. This eventually slowed the excavation activities from 120m a month to 20m a month, taking up considerable time and effort of the contractor.
Considering the complexity of work on the Atal Tunnel ─ with respect to terrain, heavy snowfall, and seismic zone ─ it was a herculean task for the stakeholders to carry out construction and monitoring activities. During the feasibility stage, RITES, along with M/s Geoconsult (an Austrian consultancy firm), did the surface studies like geological, geomorphological, and remote sensing. The planning stage saw the use of ultra-modern (Leica 350) Differential Global Positioning System (DGPS) of Snow and Avalanche Study Establishment (SASE) to check the accuracy of traverse data submitted by RITES. In order to check for any data errors from total station of Leica, a GPS network measurement was additionally made, which showed post-processing results within 3-4cms. The corrections to the drawings were subsequently carried out, and the required changes made.
The topographical layout along the high mountainous region made it difficult for any investigation to be carried out by shaft or adit. Thus, the mapping activities were executed by aerial (helicopter) survey along with off-site evaluations. All the necessary information about the site-specific characteristics was marked by these evaluations as a part of desktop studies. Eupalinos, NRG and Auto CAD Civil 3D software were used at the project site. The use of technology across the plan, design, and build stages on such a complex project led to a successful breakthrough of the project with an accuracy of +/- 5 cms.
The importance of the Atal Tunnel isn’t restricted to social benefits for locals in the region but also in ensuring efficient military movement and timely supplies. The new tunnel also trims down the recurring expenses spent on the clearance of snow and maintenance of Rohtang Pass. The all-weather route will significantly provide yearly connectivity to Spiti, Lahaul and Pangi regions. The tunnel, the world’s longest at the altitude of 10,000 feet, was opened to the public on October 3, 2020.
|Project Length||8.8 kms|
|Project Cost||INR 15 billion (approximately USD 321 million)|
|Location||Himachal Pradesh, India|
|Client||Border Road Organisation (BRO)|
|Feasibility Study||Rail India Technical & Economic Services (RITES)|
|Design and Project Management||Snowy Mountains Engineering Corporation (SMEC), Australia|
|Proof-checking Consultant (Civil Works Drawings)||3G-Vaymtech|
|Electrical and Mechanical (E&M) Contractor||M/s Savronik|
|Contractor||Strabag AG-Afcons JV|
|Instrumentation and Monitoring (I&M) Subcontractor||Encardio-Rite Electronics Pvt. Ltd.|
|Construction Technique||Drill and blast with the New Austrian Tunneling Method (NATM)|
|Shape (cross-section) of tunnel||Horseshoe|
|Emergency tunnel||2.25 m X 3.6 m tunnel beneath the main carriageway|