A Critical analysis of Silkyara-Barhat Tunnel By Maj Gen AK Chaturvedi



Himalayas– From South to North the Himalaya (Himalaya orogen) is divided into four parallel tectonostratigraphic zones and five thrust faults.  Each zone has different type of rocks and their layering which are different from the adjacent zones. From South to North, the zones and the major faults separating them are the Main Frontal Thrust (MFT), Sub Himalaya Zone (also called Sivalik), Main Boundary Thrust (MBT), Lesser Himalaya (further subdivided into the “Lesser Himalayan Sedimentary Zone (LHSZ) and the Lesser Himalayan Crystalline Nappes (LHCN)), Main Central thrust (MCT), Higher (or Greater) Himalayan crystallines (HHC). North of this lies the trans Himalaya in Tibet which is outside the Himalayas.

The Higher Himalaya, the backbone of the Himalayan mountains, is made up of 10-20 km-thick metamorphic rocks (schist and gneiss) and granites situated at altitudes of 3000 m to over 8000 m. They also have some igneous rocks.

To the south of the Higher Himalaya (the Main Central Thrust) lies the Lesser Himalaya which consists of metamorphosed sedimentary rocks (quartzite, marble, slate, phyllite, schist and gneiss) and minor volcanic and granitic rocks of Proterozoic-Cambrian age (2000-500 Ma). The stratigraphic thickness of the rock sequence in this zone is 10-20 km.

The Sub-Himalaya are foothills ranging in elevation from 250-800 m. This zone is made up of 10-km thick succession of sandstone and mudstone shed from the Himalayan mountains, and carried and deposited by rivers,

Geology of the Himalayas- It is an outcome of the immense mountain range formed by plate tectonic forces and sculpted by weathering and erosion. The Himalayas, which stretch over 2400 km between the Namche Barwa Syntaxis at the Eastern end of the mountain range and the Nanga Parbat Syntaxis at the Western end, are the result of an ongoing collision of the continental crust of two tectonic plates, namely, the Indian Plate thrusting into the Eurasian Plate. Most of the rocks are either sedimentary or metamorphic. Topographically, the belt has the highest rate of uplift (nearly 10 mm/year at Nanga Parbat), the highest relief (8848 m at Mt. Everest) and among the highest erosion rates at 2–12 mm/yr. Himalayas are relatively young mountains, just about 50 million years old. Due to continuous collision of the tectonic plates, folding is still in progress, as such they continue to rise which makes them fairly unstable and that is where they are different from Tibetan Range which is fairly stable.

Challenges of Tunnelling in Himalayas

Geological Challenges– Rocks are characterized by highly deformed, water charged, crushed, brecciated, pulverised rock mass sandwiched between two undeformed litho-tectonic blocks. Tunnelling through rock mass which is highly charged with groundwater faces major problems such as heavy ingress of water in tunnel hampers the construction, the saturated rock mass loses its strength and failure of rock mass occurs from the crown and above the spring level. Further, the high water pressure behind the tunnel periphery adversely affects the support system resulting into distress to the efforts of drilling.

Earthquakes– From the tectonic model of Himalayan region, it is clear that Himalayan Range is in a state of persistent compression due to continuing northward movement of Indian plate towards the Asian plate and there are contemporary crustal adjustments. The seismically sensitive Himalayan belt has been witnessing earthquakes of different magnitudes and intensities. Nepal had an earthquake on 03 Nov 2023, whose residual impact was felt in Uttarakhand also. Uttarakhand itself had experienced an earthquake on 03 Oct 2023.

Silkyara Bend- Barkot Tunnel

Consequent to the approval by the Cabinet Committee on Economic Affairs chaired by the Prime Minister Shri Narendra Modi, the construction of 4.531 km long 2-Lane Bi-Directional Silkyara Bend – Barkot Tunnel with escape passage including approaches on Dharasu -Yamunotri section between the Chainage 25.400 Km and Chainage 51.000 Km in Uttarakhand was cleared in Feb 2018. This 4.5 km long tunnel is being constructed in Uttar Kashi District of Uttarakhand as part of the Char Dham all-weather road project connecting four sites sacred to Hindus, and it was located on the Yamunotri end of National Highway 134. That National Highway is planned to connect Yamunotri on the south end to Dharasu on the north end. The tunnel will shorten the route by about 20 kilometres.

The collapse occurred on 12 November 2023, when a portion of the tunnel 200 metres from the entrance, collapsed.  The collapse trapped 41 workers who were working inside the tunnel. Rescue operations are led by the National Disaster Response Force (NDRF), the State Disaster Response Force (SDRF), and the police. While all possible efforts, including help from international experts and equipment especially imported for the purpose, are being made but even after 11 days rescue operations have not been able to reach fruition.


The Char Dham project, was supposed to widen roads in the region, keeping in mind sufficient slope protection needs. The project has been controversial since the start with environmentalists fearing the heavy drilling and construction was causing subsidence, landslides and heavy environmental damage in the vulnerable Himalayan region. The technique used is the Drill and Blast Method (DBM) and not Tunnel Boring Method (TBM), which has its implications. The best rock for tunnelling is hard rock but in the area of tunnel, the rock is phyllite (mostly contains clay and micaceous minerals), a very weak rock. The landslide could be the result of vibrations generated due to demolition. It needs to be noted that the TBMs work best in stable rock formations, while the Drill and Blast method can be more adaptable to varying geological conditions. In normal course the method adopted was right but in hindsight it appears that probably using TBMs would have been a safer bet.

The other critical factor is that to provide stability to those parts where tunnel work was almost completed, they used high-pressure machines to throw the concrete on the ceiling and sidewalls of the tunnel to hold the loose material from falling. While this technique gives some stability to the ceiling and side walls, but that stability is not enough to bear the load of the entire hill. They had done RCC (reinforced concrete cement) treatment only up to 200 metres from the Silkyara side. And the tunnel collapsed after 250 metres (from the Silkyara side).

As per standard operating procedure, any tunnel of proposed length of three km or more is required to have an escape tunnel for evacuation of people in case a calamity strikes. However, in the Silkyara tunnel no emergency exit was constructed, though it was planned.

The project was challenged in 2018 for its perilous impact on the Himalayan ecology. Ecological experts and environmentalists, in a petition before the Supreme Court, had raised concerns about impending environmental disasters like flooding and landslides due to the destruction of ecosystems for infrastructure projects.

In 2019, the Supreme Court formed a high-powered committee to address environmental concerns of the project. However, there was a disagreement among the committee members on the width of the hill roads and in July 2020, two reports were submitted to the top court. The Supreme Court, in September 2020, went by the recommendation that the carriageway width should be limited to 5.5 metres in the precarious terrain. The central government challenged the ruling citing national interest and argued that the road should be developed as a two-lane with paved shoulders and a width of 10 m. Eventually, the Supreme Court on 14 December 2021 allowed the double-lane paved shoulder configuration for the Char Dham road project.

The 10-metre width was a breach of the Ministry of Road Transport and Highways circular of 2018, which had advised against building full-fledged roads cutting across the Himalayan slopes and prescribed a width of not more than 5.5 metre. Experts pointed out that a 10-metre tarred road requires widening up to 12 metres and cutting mountains until 24 metres, leading to more damage to the forest and the environment.

The number of natural disasters in the region has surged since 2010. The Kedarnath disaster in 2013; repeated monsoon floods and landslides have been unprecedented, with thousands of lives lost. In Rudraprayag, earlier this year, there were numerous incidents of cracks emerging in houses and on roads, driving residents out of their homes. A case of land subsidence was also reported in Joshimath. People held protests against the National Thermal Power Corporation’s 520 MW Tapovan-Vishnugad hydroelectric project as the underground tunnel was passing near this hill town.

After this incident, geologists have once again  raised questions about the Char Dham Highway project. Geologist Naveen Juyal said mainly two types of incidents occur during tunnel construction in Uttarakhand — sudden release of large amounts of water and unexpected encounter of sheared rocks (worn by rubbing against each other).

The former Indian Space Research Organisation scientist also questioned whether geological and geotechnical studies were conducted during tunnel alignment. Such an investigation is conducted prior to any such construction and a report is provided to the construction agency. It appears that the geological survey for this project was superficial.

The Main Central Thrust (MCT) of the Himalayas passes a only a few kilometres North and Northwest of the incident site. This means that this area is extremely sensitive to earthquakes and frictional shear rocks are present in this area.

“If the environmental consequences of these schemes had been considered, the recommendations of the Supreme Court’s High Power Committee would have been implemented. Instead, the central government divided the 889-kilometer-long project into 53 sections to avoid the need for an environmental impact assessment,”.

It appears that the company entrusted with the construction, Navyug Engineering Company violated the standard operating procedure with respect to safety norms and the construction practices. Bigger question is that the NHIDCL appears to have also abdicated its responsibility of monitoring and oversite.

A serious view needs to be taken about the shortcuts taken during the planning, finalising alignment, construction and lack of the oversite mechanism with a view to ensure that such calamities are avoided in future.

Debate:  Environment protection Vs Development

Even by following every protocol, there is never a fool proof way to avoid a collapse of a tunnel being constructed. In terms of geologists, the Himalayan terrain is a new geology because it is still squeezing, which causes uncertainty and chances of sudden collapses.

“Even after all possible safety precautions, due diligence, seismic and geo technical studies, tunnel collapse while under construction may still occur. Water streaming may go unnoticed and fill the tunnel leading to tunnel collapse. In the Himalayan terrain, seismic activities, improper dumping of muck, particularly around the tunnel project are some of the reasons for such accidents,”

The government has been stressing on the strategic importance of double-lane roads for swift movement of the armed forces. For development and power security, hydel projects are also necessary. “In Uttarakhand, dam projects for hydro power generation are in progress and they are necessary for the country’s development.

It is felt that the development cannot be abandoned based on environmental concerns. There is a need to find ways and means to ensure that both coexist. In this connection, it needs to be remembered that even in past most of the major shrines came up in Uttarakhand without causing damage to the environment. 

Case of China

As explained earlier it is the geology of Tibet, which is fairly stable, helps China is building roads and helipads on its side leading to recent security challenges for India on the Indo-China border.

Aftermath of Disaster

Inquiry– A team of geologists from the state government and educational institutions went to the scene in order to determine the possible cause of the incident. The Uttarakhand government has formed a six-member expert committee to investigate the cause of the collapse of the section of tunnel. The committee, led by the Director of Uttarakhand Landslide Mitigation and Management Centre, will examine the reasons for the collapse in the Silkyara Tunnel.

Relief Work– The government has been trying to drill through the debris to rescue trapped workers. It is felt that the trapped workers will come out as quickly as possible.

In this connection, wide steel pipes about 900 millimetres in diameter have been pushed through the rubble to deliver oxygen, water and small food packets to the trapped workers, according to the district administration. The workers are safe and communicating using walkie talkies, officials said.

Tunnels Connecting Ladakh 

Srinagar Axis

  1. Z Morh Tunnel– Work on a 6.5 km two lane bidirectional tunnel at Z Morh in Ganderbal district of J&K connecting Sonamarg and Gagangir is in progress. It is designed to allow 1000 vehicles/ hour at a speed of 80kmph. The cost of this project is 2717 Cr. Although official PDC is 2023 but the likely PDC is middle of 2025.
  2. Zojila Tunnel-it is planned to be a two lane 14.2 km long tunnel connecting Sonamarg and Minimarg is in progress. Once completed it will reduce the travel time by 2.5 hrs. 40-45% of the work has already been completed. The work on this tunnel had commenced in Oct 2020 and the PDC is Sep 2025.  It has been informed by some unconfirmed sources that the PDC has now been pushed to 2030.

Darcha- Padam- Nimu Axis

Shinkun La pass located on this road at a height of 5091 meters, is another limiting factor towards the road becoming an all weather road. Now the construction by BRO for a 4.5 km long tunnel at Shinkun La is about to start (July 2022) with PDC of 2025. The importance of this road lies in the fact that 14-16 hours taken currently for travelling from Manali to Leh will be reduced to 10-12 hours.

As per earlier reports, this tunnel was supposed to be 13.2 km. It needs to be clarified by the concerned agencies the reason for the reduction in length. Is it because of a change in alignment or taking the tunnel to a higher altitude? Raising the altitude will defeat the purpose of a tunnel as the approach will become snowbound during winter. Change of alignment will result in additional road construction, which may impact the PDC. These issues need to be clarified by the BRO, who is building this tunnel.   

Manali- Leh Axis-

On this road following passes are there-

  1. Rohtang Pass– Atal Tunnel at an altitude of 3000 m has already been completed, it is 9.02 km long. It is 10.5 m wide with Over head clearance of 5.5 m. This tunnel should be taken as a ‘Bench Mark’ and for similar geology construction practices used in this tunnel should be considered for execution.
  2. Baralachala– Feasibility of a 13.7 km tunnel has already been completed. Sanction to start the construction is awaited.
  3. Lachungla and Taglangla– Survey work for tunnels at these two passes is in progress.

Other Tunnels

  1. Sela- Ready waiting for inauguration.
  2. Saser La- DPR under preparation is important to connect Sasoma to DBO.
  3. Hamboting La and Ke La- DPR Ready, waiting for GoI sanction. It will provide another axis from Kargil to Leh. Ke La connects Zingral to Tangtse.


Development is essential but it has to be in sync with environmental conservation. Construction practices need to take into account the geology of the area without compromising the standard operating procedures for construction as well as safety.

Pl Watch-

STRIVE Def Dialogues: EP 84


Author – Maj Gen AK Chaturvedi, AVSM, VSM (Retd)  is a retired Indian Army General Officer who has served in Jammu & Kashmir, NE, Andman Nikobar on various appointments at Command and Army HQs. . He is Vice Chairman of Think Tank, “STRIVE”,  after retirement is pursuing his favourite hobby of writing for newspapers, journals, and think tanks.

Disclaimer: The views expressed are those of the author and do not necessarily represent the views of the organisation that he belongs to or of the STRIVE. 

3 thoughts on “A Critical analysis of Silkyara-Barhat Tunnel By Maj Gen AK Chaturvedi

  • November 26, 2023 at 9:48 am

    Rescue work which is in progress, raises many question. It appears that in their concern to quickly rescue the trapped labourers the efforts are being made more to show that efforts are being made rather than rescue be the main objective. After all if auger encountered obstacle how these aspects were not anticipated because these days we do have Doppler/ penetration radars. Also, I hear that probability of using a vertical intervention is also being explored. I feel that it would not be useful because first boring 83 meters itself will not be easy second because of state of rock profile possibility of collapse will become more distinct.

  • November 25, 2023 at 5:53 pm

    Blade of Auger has broken and NHIDCL is attempting to do vertical drilling. My recommendation is that BRO which has substantial experience in tunnel boring should also be incorporated in the rescue operation.

  • November 23, 2023 at 11:39 pm

    Accountability of NHIDCL and Navyug engineering has to be fixed. Also it is my firm view that Navyug probably did not cater for proper accomodation for labours and as such probably they were resting in the tunnel because at 0530 h in the morning it beats my logic that they were working. Also, normally when work is done in a tunnel generally strength is not more than 10-12 people, albeit they are rotated.

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