The Silkyara-Barkot tunnel is a crucial component of the ambitious Char Dham all-weather road project initiated by the Central Government. Spanning 4.5 km between Silkyara and Dandalgaon, it is a vital segment of the Brahmakhal-Yamunotri section. Unfortunately, what was intended to enhance connectivity among the four significant pilgrimage sites known as Char Dham — Kedarnath, Badrinath, Yamunotri, and Gangotri — through an extensive 889-kilometer road network, became a site of tragedy when a section of the tunnel collapsed on November 12.
The construction of the tunnel was entrusted to the Hyderabad-based Navayuga Engineering Company by the National Highways and Infrastructure Development Corporation Ltd (NHIDCL), a fully-owned company of the Ministry of Road Transport & Highways, Government of India.
Geological Challenges in the Himalayas
Since the tunnel’s commencement in December 2016, geological challenges have surpassed initial predictions, confirming findings from supplementary exploration measures conducted at the project’s initiation. Controversies have marred the venture, with environmentalists expressing concerns about the potential detrimental impacts of extensive drilling and construction undertakings. Worries include the possibilities of subsidence, landslides, and significant environmental degradation in the ecologically sensitive Himalayan region.
The Himalayas, a geological marvel, is the youngest and highest range of fold mountains globally, originating around 40-50 million years ago. Characterized by high seismic activity, it experiences continuous growth from the ongoing collision between the Indian and Eurasian tectonic plates. The Silkyara tunnel is situated within the lesser physiographic zones, close to the main central thrust of the Himalayas, a major geological fault (zone of fractures). The tunnel traverses highly sheared and extensively deformed lithology, including metasedimentary rocks such as phyllite, slate, and metasiltstone. Quartz veins, ranging from less than 2 cm to 10 cm in thickness, traverse the country rock primarily along the foliation plane. The hill slope, with an angle between 50°-60°, is covered with overburden supporting moderate vegetation, predominantly evergreen pine trees. The outcrop is concealed beneath approximately 3m of weathered slope wash materials. Research findings indicate that topsoil erosion in the Himalayas occurs at a rate three times higher than the national average, suggesting a structurally vulnerable region due to fractured and fragile rocks with numerous joints. The diverse rock types in this area, varying in strength from exceptionally soft to more hardened, pose a challenge, with the softer rocks prone to crumbling, contributing to the inherent instability of the region.
Rescue Operation in Delicate Geology
The proposed Silkyara-Barkot tunnel encounters rocks with inherent weakness, necessitating a robust support structure to reinforce these vulnerable formations. Based on surface geological assessments, it is anticipated that the encountered rock types along the diversion tunnels will comprise 20% good (Class 2), 50% fair (Class 3), 15% poor (Class 4), and 15% very poor (Class 4), as outlined in the report.
On November 12, Silkyara tunnel, one of the under-construction tunnels of Chardham all-weather road project collapsed, trapping 41 workers. Operation Zindagi (life) was launched by the Uttarakhand state government to rescue the trapped workers. Rescuers needed to dig through 59m of collapsed debris to excavate the trapped workers. To expedite the rescue process, first horizontal drilling machine with an auger bit (to install an 800mm escape pipe) was deployed. Then, the rescue team sought advice from experts who had successfully saved students from the Tham Luang cave incident in Thailand in 2018.
Cracking noises reported on November 17 prompted the suspension of drilling through the debris in the tunnel. Alternative access tunnels were started parallel and adjacent to the existing main tunnel. Three pipes were bored during the procedure: one for oxygen, one for food transit, and a 15-centimeter-wide (6-inch) conduit for hot meal delivery and endoscopic camera insertion. The Border Roads Organisation built a 1.15-kilometer (0.71-mile) road to a position on a hillside above the tunnel on November 19 while preparations were underway to dig a vertical shaft to facilitate rescue operation. Drilling was delayed on November 22 and 23 with major repairs to the drilling machine and its mounting platform needed on November 23 due to issues with the consistency of the rubble and obstructions.
At this point, it was thought that the operations had progressed approximately 75% of the way through the obstructing debris. After successfully digging 47 metres (154 feet) down the tunnel, the tunnel drilling machine failed and became trapped within, hence impeding the progress of the drilling and posing another challenge to the rescue mission on November 25.
In order to cut through the rubble and get to the trapped workers, the rescue team opted to clear the final muck of approximately 12m manually. Drilling was stopped around nine metres (30 feet) short of breaking through. Arnold Dix, an Australian tunnelling expert who was involved in the rescue attempt, also advised the rescue team to proceed with caution. Different techniques to gain access to the workers were intensified on 27 November. At the Silkyara end, Satluj Jal Vidyut Nigam’s vertical drilling reached a depth of 32 metres (105 feet), and Rail Vikas Nigam was laying a third pipeline to supply workers with requirements. While Oil and Natural Gas Corporation (ONGC) was getting ready for vertical drilling, Tehri Hydro Development Corporation Limited (THDC) India Limited successfully completed a drill on the Barkot end of the tunnel that reached a depth of 12 metres (39 feet).
On November 28, the rescue team called ‘rat-hole’ miners who managed to smash through the last section of debris and manually push a pipe to the workers who were trapped. Over the course of 17 day, the rescue crew evacuated every worker individually on stretchers.
Dix, after the course of the long-drawn operation, said the successful rescue of the trapped workers was a ‘miracle’. Dix was also seen praying for the safe evacuation of the trapped workers in Uttarakhand. He also said in an interview that the Silkyara tunnel rescue operation was like an epic wherein the mountain was controlling everything. “It’s like an epic from 3000 years!”
*Prof Amit Kumar Verma is xxx and Amit Jaiswal is xxx
