Uttarkashi: A year ago, on the same day, on the occasion of Diwali, Uttarakhand’s Uttarkashi district had witnessed a massive under-construction collapse which entrapped 41 workers inside the tunnel.
Last year, on November 12, a section of the Silkyara Bend–Barkot tunnel in Uttarakhand, collapsed, trapping 41 workers for 17 days. A 21-day-long humongous rescue operation involving national and international agencies had saved the lives of these workers.
Silkyara tunnel, a part of all-weather Char Dham road project
In March 2018, the Ministry of Road Transport & Highways (MoRTH) initiated the construction of a 4.5 km tunnel between Barkot and Silkyara at Dharasu Bend, near National Highway 134 in Uttarkashi, with a budget of Rs. 1,383 crores. This tunnel is a crucial component of the central government’s ambitious All-weather Char Dham project in Uttarakhand. The construction of this tunnel is aimed to connect the Yamunotri and Gangotri valleys to facilitate travelling during pilgrim season. The National Highways & Infrastructure Development Corporation Limited (NHIDCL) and Navayuga Engineering Company Limited are the key agencies in construction of this tunnel.
Tunnel collapse in the morning of Diwali festival on 12 November
The under-construction Silkyara tunnel on the Yamunotri highway in Uttarkashi, Uttarakhand, gained national and global attention on November 12 last year. On that day, a section of the Silkyara Bend–Barkot tunnel collapsed, trapping 41 workers for 17 days. This incident occurred on the morning of the Diwali festival. In the early hours of November 12, 2023, around 5:30 am, 41 workers were performing reprofiling work between 260 and 265 meters inside the tunnel from the Silkyara side. Suddenly, a 55-meter section between 205 and 260 meters collapsed. With the portion beyond the collapse still unfinished, there was no way for the workers to exit from the other side. During the collapse, some of the workers managed to come out but 41 workers remained trapped inside. Initially, the debris started falling slowly and was not taken too seriously up until the entire tunnel was blocked suddenly.
A major rescue operation was launched involving various agencies and international experts
For over 16 hours, the site lacked the necessary machinery and equipment to conduct the rescue operations swiftly and efficiently. The rescue team worked tirelessly, continuously removing landslide debris and using the shotcrete method to stabilize the affected section. After this tunnel collapse, the Uttarakhand government and central government initiated a rescue operation along with national agencies like Oil and Natural Gas Corporation (ONGC), SJVN, RVNL, THDC, Indian army, Airforce, BRO, NDRF and SDRF.
An auger drill had been built, flown in from Delhi, and put into action by November 16
With the help of a pipe, authorities provided food and oxygen to the stranded workers just one day after the tunnel section collapsed. By November 16, an auger drill had been flown in from Delhi and put into operation. Over the next week, efforts to reach and rescue the workers faced intermittent challenges as officials navigated obstacles in the drill’s path, maintained its condition, ensured platform stability, and monitored the impact of vibrations on surrounding rocks. They had to be cautious to avoid endangering the workers with dislodged rocks. Unfortunately, by November 25, the drill’s blades became stuck in the rubble, halting the project.
Vertical drilling to rescue the workers
With the help of agencies like ONGC and SJVL, the rescue teams made attempts to drill the tunnel vertically and create an escape route, but, the vibration of heavy drilling machines posed another danger of further collapse inside the tunnel which could have become more threatening to the lives of the workers. Therefore, this plan was dropped and other methods were explored for the safe evacuation of the workers. Finally, rat-role mining techniques were suggested by some of the experts and these technicians were called from Delhi to take the rescue operation ahead.
Rat-hole minors helped remove the debris and rescued 41 workers on 28 November
Rat-hole mining specialists played a crucial role in removing the debris. By November 28, rescuers successfully punctured the tunnel, allowing the trapped workers to be carried out. The rescue operation was remarkable, not only because of the successful extraction but also due to the significant resources mobilized to achieve it.
Major factors behind this collapse
The collapse was attributed to a combination of geological and structural factors, including hidden loose patches of fractured or weak rock, water seepage, and undetectable issues during construction. Despite advanced safety measures, the incident highlighted the inherent challenges of tunnel construction in such terrain. Key factors behind the accident included the project’s misalignment, placing it along a ‘shear zone,’ and the contractor’s failure to take adequate precautions during ‘re-profiling’ work, despite the known vulnerabilities from previous collapses. Additionally, the inadequate deployment of sensors and instruments contributed to the accident.
Investigation about tunnel collapse
Following the incident, a detailed report was submitted to the Union Ministry of Road Transport and Highways, outlining several key factors that contributed to the unfortunate accident. The investigation, conducted by a six-member central team between December 13 and 15, meticulously examined the causes and revealed significant deficiencies in the construction process. The report highlighted the selection of an incorrect alignment in a shear zone, inadequate safety measures during re-profiling, and a failure to learn from past accidents as the primary reasons behind the mishap.
Absence of essential sensors and equipment inside the tunnel
The report also revealed a critical issue about the absence of essential sensors and equipment inside the tunnel. It also highlighted inadequate monitoring by NHIDCL (National Highways & Infrastructure Development Corporation Limited) officials during construction. This incident, which occurred on November 12 due to a landslide, exposed significant lapses in the construction process.
Tunnel work resumed after two months
Construction work at the tunnel, which had been suspended since its partial collapse in November 2023, resumed after more than two months in January this year. With permission from the Union Ministry of Road Transport and Highways, protective construction efforts have begun from both the Barkot and Silkyara ends of the tunnel. The accident has delayed the tunnel’s construction progress, and the National Highways & Infrastructure Development Corporation Limited (NHIDCL) now estimates that the project will be completed by 2026.
