Uttarkashi tunnel disaster: Expert panel's observations point to weak shear zone

Preliminary observations of the six-member expert panel on the Uttarakhand tunnel disaster indicated that construction was caught in a 'shear zone' situation and lacked the required escape route or piped passage in case of emergencies, it is learnt.

As per guidelines, any tunnel of more than 1.5 km must have an escape passage for emergencies.

Project proponents claimed that there was a piped escape passage in place until a few days before the tunnel collapse, but it was removed for some reason, it is learnt.

The tunnel collapsed on November 12 and an expert committee was set up on November 14.

Key to the collapse was in all probability the 'shear zone' it hit, first expert observations indicated.

Debris observed at the tunnel collapse site shows the metamorphic phyllite rock in pulverised form, as per preliminary observations.

This 'shear zone' was probably missed at the time of inspections before drilling began. However, a proper assessment of the support system at the construction site can be done once the rescue and evacuation work have been completed.

ET has learnt that the observations have also called for real-time monitoring systems and safety audits of all similar constructions in the area. The same has already been announced by the state government and National Highways Authority of India.

The 4.531 km '2-Lane bi-directional Silkyara bend-Barkot tunnel with escape passage', including approaches on Dharasu -Yamunotri section, was approved by the Union Cabinet in February 2018.

The idea was to provide 'all weather connectivity' to Yamunotri, part of Uttarakhand's Chardham Yatra, and to encourage regional socio-economic development, trade and tourism within the country, a Press Information Bureau statement from 2018 read.