Friends, you will recall that in November 2023, the under-construction Silkyara Tunnel collapsed in Uttarakhand, which led to 41 workers being trapped for 17 days. In the end, after 17 days, they were all rescued with great difficulties. (An earlier blog on this collapse was written on 29th November 2023). This 4.5 km long tunnel is part of Char Dham Yatra-all weather road linking pilgrimage sites Gnagotri and Yamunotri. Constructed by National Highways Infrastructure Development Corporation Ltd. (NHIDCL) through Navayuga Engineering Company Ltd, the estimated cost was approx Rs 854 Cr, it was supposed to shorten the distance between the shrines by 26 km and travel time by one hour through steep mountain.
In December 2023, the Ministry of Road Transport and Highways (MoRTH) constituted a five member committee to investigate the collapse of a portion of the under construction Silkyara tunnel in Uttarakashi are of Uttarakhand. The committee was headed by RK Dhiman, Additional Director-General Border Road Organisation (BRO), the other members were Sandeep Gupta, Chief Administrative Officer, Member Udhampur-Srinagar-Baramulla-Rail-Link project, Prof (retd) KS Rao, IIT_Delhi, Prof Amit Srivastava, Delhi Technological Unversity, and Rahul Gupta Chief Engineer, MoRTH New Delhi.
This panel was asked to review the Detailed Project Report (DPR) and detailed design submitted by the contractor along with geotechnical and geophysical investigations conducted during DPR. The panel was also asked to assess entire system of project implementation by the contractor including quality control. The panel was also to assess te safety measures taken during construction of the tunnel and identify lapses, if any. It was also to assess the desirability of construction of separate escape tunnel.
The committee was also asked to recommend amendments to Standard Operating Procedure (SOP) to be followed in case of tunnel collapse and safety measures to be taken-up during tunnel construction.
This government-appointed panel panel’s final report on this tunnel collapse, found that several factors contributed to the collapse including:
Incorrect Rock Mass Rating
The rock mass rating (RMR) was incorrectly used to classify the rock mass Class-IV instead of Class-V, which was primary cause of minor collapses.
Lack of Monitoring
There was no adequate monitoring plan, which led to incorrect deformation details and a lack of proper addressing of deformations.
Reprofiling without Safety
Reprofiling was done in the distressed areas without ensuring the safety of the workers.
Reprofiling is a method used in tunnel construction to repair anomalies and re-establish desired clearance. It is done without changing the surrounding rock
Absence of Senior Geologists
Senior Geologists and materials engineers, who are important for identifying geology and ensuring quality, were absent for a year.
The final report also found negligence on part of the entity that prepared the DPR, Construction firm, Supervision Consultant or Authority Engineer, and NHIDCL. The report said that fixing of alignment did not meet did not meet basic principles of tunneling, and there was negligence on part of the contractor to address the issue of 21 minor collapses, despite Authority Engineer (AE) flagging them.
The report also flagged incompetence of contractor, AE, and approving authority NHIDCL, mentioning that evidence showed no measure was taken to address shear zone issue. In tunneling, shear zone refers to highly deformed, weak and thinned rocks due to high level of regional stress, and such zones require special attention, greater monitoring of ground behavior and more support to avoid mishap.
For completion of this project, the panel has recommended clearing off debris in the collapsed sections of the tunnel for condition assessment. It has suggested immediate dewatering, and redesign and modification of the construction methodology to align geological conditions.
The construction work on the tunnel was resumed within two months of collapse, after the interim report was panel was received. As per reports of last month, the issue of debris accumulated has been addressed and full fledged construction will be able to resume by October 2024.
Finally, with this report one thing that has come into open, that all the agencies involved in this project had a very casual approach to the construction of tunnel. Hope all of them have learnt a lesson in a hard way.
Waiting for your feedback on this blog.
Anil Malik
Mumbai, India
26th September 2024