The Silkyara Tunnel Incident : Questions need to be seriously( and sincerely probed now that the trapped workforce of 41 is safely evacuated after a laudable effort by the rescue team.
*Disclaimer: This article is based on information available in the public domain as open source. Idea of this article is purely to understand " what seems to have gone wrong".
This is a 4.5 km long tunnel , part of the Char Dham Pariyojana to improve connectivity to four pilgrimage sites and is located in Uttarkashi District. Based on information available in the public domain, apparently following safety lapses have happened in this project:
- Preliminary findings suggest that the collapse may have been caused by geological fault (shear zone). It should be noted that the tunnel is located in upper Himalayan region ( where Uttarkashi district is located) and is in proximity of Main Central Thrust ( MCT) i.e. a geological fault line where the Indian peninsular plate is pushed beneath the Eurasian plate, stretching over 2,000 kilometers along the Himalayan line from northwest to southeast. Consequently, the area experiences significant shear stress due to continuous tectonic plate movement. In simpler terms, this becomes an area prone to high seismic activity.
- A noted geologist, Dr. C P Rajendran has said that Uttarkashi and surrounding areas have previously experienced some major seismic activity including a 7.8 magnitude earthquake in 1803 and a 7 magnitude earthquake in 1991. He further says thatTunnel seismic prediction (TSP), which involves a seismic survey before initiating a new phase of the tunnel and also helps maintain safety during construction, was not taken into consideration in case of the Silkyara tunnel.
- As per a report by a Supreme Court appointed expert committee in July 2020 has said that the impact of the whole project was not properly assessed before the construction started. As per Mr. Hemant Dhyani who is member of this committee, said that the recommendations to build a narrow tunnel of 7-8 meter width has been ignored leading to more blasting and more risk of collapse. It further says that more than 200 likely landslide locations have been created due to hill excavations, dumping of debris and choking of water flow during the whole project.
- One major lapse is the construction company did not construct a safety exit route which was required as per the SOP. On-site observations have revealed that, according to the proposed plan, an escape route was indeed planned for the 4.5-kilometre Silkyara tunnel, but, it was never implemented.
- On-site reports have revealed that no trench cages or safe tubes were used for the workers working in unprotected parts of a trench. Trench cages serve a crucial role in safeguarding workers from potential cave-ins.
I reiterate, the intent of this article is not to criticise any government , company etc. but rather to understand the engineering aspects. I have been a HSE professional for close to three decades and what our profession thrives is to get in depth knowledge on the reasons for the incident and most importantly how potential disasters are avoided. Whenever an accident happened on a factory location, the amount of time for appreciating the rescue operations and a great deal of time is spent on probing what went wrong. Have a great day ahead!
