Saturday, February 24, 2024

Uttarakhand Tunnel : Collapse and Rescue

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Recently, in the early hours of November 12, an under-construction Silkyara-Barkot tunnel (Uttarakhand Tunnel) along the Yamunotri National Highway in Uttarkashi district, Uttarakhand, collapsed, trapping a significant number of workers inside. The 4.5 Km tunnel is a part of Char Dham Pariyojana to help improve connectivity of the four pilgrimage sites. The construction was tendered to 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.

Potential Causes of its Collapse-

  • Though it is at a shallow depth of 140 meters and one does not expect much stress, still it is situated near the Main central thrust (a geological fault, where the Indian Plate pushes beneath the Eurasian Plate, and in the upper Himalayan region.) Shear stress accumulation around this thrust fault is very high and it sees continuous tectonic plate movement.
  • It is in an area with hard and soft rocks, and hence needed additional support. In such projects, New Austrian Tunnelling Method (NATM) is used as it provides a flexible support system of girders, shotcrete and rock bolts. However, in this case apparently, traditional uniform support system was used.
  • Instrumentation for real time monitoring during construction work is crucial as it alerts the experts regarding any kind of deformity inside the tunnel. It appears that the contractors did not provide proper instrumentation. Such monitoring also provides insights with respect to any convergence beyond the calculated allowable limit. If a tunnel collapses it means probably the calculations or the monitoring was flawed.
  • Elevation adds risks and therefore, in such cases, detailed assessment reports are made and then submitted to the government for approval. The report must include through assessment including – tunnel seismic prediction (TSP), assessment of rock mass and rock behaviour. According to Dr Naveen Juyal, a geologist with expertise in the Himalayan region, said, “First of all if the 4.5 km road tunnel project in the sensitive Himalayan region was taken up based on this geological report, it is insufficient. One can’t know the type of rocks by just three exploratory drilling”. Another geologist, Y P Sundiryal, stated that – “According to the report, the type of rock in the area where the tunnel is built is weak like slate and siltstone”. Thus, appropriate planning and a construction support system are required. It appears that the Silkyara’s implementing agency disregarded it.

India is equipped with all the systems required to guarantee that tunnels are constructed correctly.

Nevertheless, accidents like this tunnel collapse happen as a result of the carelessness of the project heads, the project proponents and the contractors’ negligence in making sure that all safety measures and established procedures are followed.

Efforts made by Government in Rescuing its Citizens-

  • NHIDCL Lifeline Efforts: – Freshly cooked food, fruits and medicines are being inserted inside the tunnel at regular intervals using the 2nd life line (150 mm dia.) service. Modified communication system with wire connectivity developed by SDRF is being used for communication regularly and the people inside have reported that they are safe. They were given mobile phones and board games to make them engaged through the last phase of the rescue operation. Thus taking care of their physical as well as mental needs.
  • Vertical drilling by SJVNL – Vertical drilling had to be started after an auger machine used for horizontal drilling broke down and got stuck in the debris. IT would help provide direct access to ventilation and communication. A DRDO Team from Hyderabad with Plasma and glass cutter had arrived on site and the cutting was started simultaneously.
  • Manual drilling- After the Auger machine broke down, rescue teams decided to pursue multiple strategies simultaneously. Manual drilling is aimed at completing the task the auger drill started. For this task, an 11-person team has been flown in from Delhi. Six of these are specialists, and there are five more on standby. Rescue crews stated they would manually remove the debris by entering the 800-mm pipe. These professionals are also called rat miners for their rat-like skill in boring. Other methods like building a mini tunnel along the left side of the tunnel is also being employed. This mini tunnel will be perpendicular to the Silkyara tunnel, and the plan is to rescue the trapped workers through it
  • Road Cutting and Supportive Work by BRO-BRO has completed construction of an approach road for vertical drilling by SJVNL and RVNL. It is also building approach road for ONGC with geological surveys conducted by ONGC and a 1050 meters of approach road has been constructed so far out of 5000 meters.
  • A Drift Tunnel by Manual-Semi Mechanized Method is being built by a Joint Team of THDCL /Army/Coal India and NHIDCL. Drones and robotics are being used to monitor the situation.
  • Oxygen supported hospital beds have been prepared in Uttarkashi, where the 41 workers will be taken after rescue.

From calling global experts to importing robust machines and synergising various agencies like- ONGC, NHIDCL, SJVNL, THDCL, DRDO and RVNL. The government has been sensitive and has been taking steps since day one with The PMO and the Union Minister Nitin Gadhkari, directly monitoring the operation. Though, it is clear that all the possible actions are being taken for the rescue operation. The problem throws a larger question on our approach to disaster management, risk assessment and mitigation. While disasters are unforeseen, the approach towards risk assessment and mitigation is more important.

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