Rohtang Pass Tunnel Case Study – Geotechnical Monitoring & Instrumentation

Rohtang Pass, now known as Atal Tunnel,  is a very famous and popular mountain pass, almost 13,058 ft, situated on the eastern Pir Panjal Range of the Himalayas around 51 km from Manali. Especially known for its mesmerizing landscape, the pass connects the Kullu Valley with the Lahaul and Spiti Valleys of Himachal Pradesh, India.

Known for its scenic beauty, Rohtang Pass holds strategic importance for India. Every year, during July to September, the road becomes a passage to the people of Lahul valley transporting their cash crop, potatoes and peas to the markets across Atal Tunnel to Kullu and earning money for the unstable weather period of 9 months.

The construction of the tunnel was very much awaited and was finally inaugurated on Oct 3rd 2020 by India´s Prime Minister Narendra Modi.

Now that we have introduced the Rohtang Atal Tunnel, let’s see Encardio-rite’s project overview, the instrument used, and the services provided.

Project Overview:

Rohtang-Pass-Tunnel

Recognized as one of the highest trafficable passes in the world, the Rohtang pass is designed to create an all-weather route to Leh and Lahaul and Spiti valleys in Himachal Pradesh. The Rohtang Pass Highway Tunnel is situated in the Western Himalaya region of Northern India with its altitude of 3,980 m. With a length of 9.02km, it is also the longest tunnel in the world at an altitude of over 3,000 metres or 10,000 feet above mean sea level.

For about four months, the pass is covered with white sheets of heaviest snowfall and blizzards, making the route inaccessible for anyone.

Renamed after the former Prime Minister of India, Mr. Atal Bihari Vajpayee, the tunnel reduces the travel distance from 4 to 6 hours to only 30 minutes. It also reduces the distance between Manali and Keylong by about 46 km (28.6 mi).

The Rohtang Atal Highway Tunnel with its 8.8km of length is the longest road tunnel in India situated at a high altitude. Apart from high altitude and uncooperative climate, the geological condition in the Himalaya was a big challenge faced by the Encardio Team. Braving the freezing weather, snowfall, frequent floods and thin air, the team soldiered forward, providing with the most accurate sensors and instrumentations.

The rocks found within the tunnel area are mainly schist and migmatite with expected disturbed zones and in some individual areas, high squeezing rock was also found.

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Rohtang Pass Tunnel Details:

Shape (cross-section) of the tunnel: Horseshoe

  • Finished width: 10.00 m (32.8 ft) at road level.
  • Construction technique: Drill & Blast with NATM.
  • Overburden: Maximum 1,900 m, average more than 600 m.
  • Emergency tunnel: A 2.25 m high and 3.6 m wide emergency tunnel is integrated into the tunnel cross-section beneath the main carriageway. There are 18 egress tunnels, with an opening after every 500 metres in case of any hazard or emergency.

    Other safety measures include 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, air quality monitoring at every one Km, evacuation lighting/exit signs and broadcasting system throughout the tunnel among others.

  • The Atal Rohtang Tunnel will be able to take a traffic of 3000 cars or 1,500 trucks per day, capping the speed limit at 80 km/hr. It also has the state of the art electromechanical system including a semi-transverse ventilation system.
  • There are pollution sensors in the tunnel that monitor the air quality in the tunnel. If the quality is below the recommended level, fresh air is injected into the tunnel with the help of two heavy duty fans on each side of the tunnel.

Monitoring Services for Rohtang Pass Tunnel

Encardio-rite was awarded the subcontract for the complete monitoring solutions for the tunnelling work. Let’s have a look at its monitoring solutions.

Being an expert and experienced in geotechnical monitoring, Encardio-rite provided world-class monitoring services during tunnelling. Apart from that, their team also made sure that they were one step ahead of any mishap by continuously conducting geophysical prediction by Tunnel.

Seismic Prediction System (TSP) before tunnelling which recognizes any early signs of fault or fracture zones, or zones where the rock mass characteristic changed. A geological prognosis could be given that enabled the tunnel site management to determine necessary forthcoming tunnelling measures.

Apart from that, a number of turnkey services were provided which are listed below.

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Turnkey Services for Rohtang Pass Tunnel

    • Supply and installation of geotechnical instruments
    • Tunnel seismic prediction by TSP
    • Weekly and monthly reporting with evaluation & interpretations

Encardio-rite uses a list of instruments during the monitoring phase of the Rohtang Pass Tunnel. Have a look at it below:

Instrument Used in Rohtang Pass Tunnel:

    • Multi-point extensometer: This particular instrument was used for monitoring of rock settlement. 3-4 points MPBX were installed at the north portal site at different chainage of the Rohtang Pass tunnel. The reading of the extensometer presented and helpful information about rock behaviour and its monitoring.
    • Load Cell: This instrument helps to convert force into measurable electrical output. Load cells were installed at a few locations near the 3-point extensometer to correlate the data.
    • Bi-reflective target: Installed to measure convergence, these were placed throughout the tunnel at different arrays.
    • Tunnel Seismic Prediction System (TSP): TSP measurements were applied at both the North and South portals at an interval of 80-100 m. In most of the survey predictions, the range was able to reach 50 to 100m ahead of the tunnel face in order to fulfil a sufficient coverage of pre-information. The conclusion was that TSP was an invaluable tool that helped to obtain additional important information on the condition of the rocks which had to be excavated. TSP made is successful to achieve sufficient quality data with a prediction range of 50 to 100 m ahead of the tunnel face.

Apart from the monitoring services, turnkey services, and supply and installation of geotechnical instruments, an experienced and proficient I&M Encardio team was placed on the site to rapidly deliver reliable data and information, thereby ensuring the safety of people, structures, and construction.

Monitoring reports included interpretation of variations observed in instrument data and the factors likely to affect their behaviour e.g. construction, rock movement, etc. Such crucial information was provided to the contractor regularly.

The Rohtang Pass Tunnel is expected to be open for public later this year. It will definitely lead to a boost in tourism in the region. Apart from that, it will also connect the natives of Lahaul and Spiti valleys to the rest of the country as the tunnel will be functional even during the harsh weather conditions.

This was all about the longest and the most ambitious tunnel in India. If you’ve any questions or doubts, feel free to comment below.

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