Due to Cost and Time Concerns, Silkyara Tunnel Project Said No to Separate Escape Tunnel: Report

New Delhi: Last month, 41 workers were trapped in the Silkyara-Barkot tunnel in Uttarakhand for 17 days. A late environmental impact assessment (EIA) report, reviewed by the Indian Express, revealed that the situation might have been avoided if the option of a separate escape tunnel had not been ruled out due to cost and time concerns.

While weighing options for the “best-suited cross-section” of the tunnel, the EIA report rejected – as “not recommended at all and ignored” – a “separation wall” at the centre of the tunnel’s carriageway along with “egress openings” for “escape” during an emergency, the newspaper reported.

It instead recommended the original project plan: A dedicated 3.5m escape channel separated by a concrete barrier from a 7m carriageway meant for two-way traffic inside a D-shaped tunnel.

But, as reported by the Indian Express, this design was later modified during the construction, apparently for better space utilisation and traffic safety.

“Instead of leaving an escape channel on the left, we put the divider in the middle of the tunnel for single-way traffic on either side. This created more space for traffic and eliminated the risk of head-on collisions,” a senior project engineer told the daily.

A tunnelling expert involved in the rescue operation last month pointed out that a total blockage of the Silkyara tunnel made “the positioning of the divider” immaterial and only a separate evacuation tunnel could have helped.

“A situation like this (collapse) requires a separate evacuation duct running next to the main tunnel with access at regular intervals, or a few lateral inclined escape adits rising to the ground surface. Having an escape passage in the same tunnel helps during traffic or fire incidents, but not if there is a total blockage,” the expert told IE.

"The construction time and cost required is more for two tunnels, two portals and two sets of ventilation systems. This system is best suited in case of heavy traffic volume but at current location, the traffic volume is only 2000 PCU (passenger car units). Hence this proposal is also not recommended,” the EIA report said.

Also read: If Lessons Are Not Learnt, Expect More Silkyaras

The Ministry of Road Transport and Highways submitted the 208-page rapid EIA report to the Supreme Court in September 2020. By then, the Silkyara tunnel was “already under construction and more than 15% of the work has already been completed”.

“Since work was already on, the rapid EIA report reflected the project plan. For the rescue channel, too, it rejected the options not on the card. It could not have predicted that the project would go on to drop the escape channel altogether,” a consultant involved in the EIA process told the daily.

The Silkyara-Barkot tunnel is part of the 889-km Char Dham project. The Bharatiya Janata Party-led National Democratic Alliance  government split the project into 53 separate sections, none over 100 kilometre in length, and evaded the need for an environmental impact assessment.

In 2013, the Congress-led United Progressive Alliance had decided to waive environmental clearances for road projects less than 100 km long. Three years later, the NDA made use of this waiver.

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