SLBC Tunnel Tragedy: Plans to gain access to the trapped workers by drilling from top ruled out

Alternative plans to reach them are proving equally unsafe due to the complex geological conditions of the Tunnel site

Hyderabad: Despite three days of relentless efforts, access to the trapped workers and engineers inside the Srisailam Left Bank Canal (SLBC) tunnel project remains elusive. Alternative plans to reach them are proving equally unsafe due to the complex geological conditions of the accident zone.

Multiple agencies with expertise in handling such emergencies are at work, but no significant headway has been made so far.

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The workers are just 10 to 15 metres away from the tunnel end, where further boring work has to be resumed. Reaching them is still a daunting task, compounded by the tunnel sloping towards the end adding to the water logging problem.

Initially, drilling from the top to access the accident location was considered a possible option. However, the scope for such an exercise has ultimately been ruled out.

The tunnels traverse a highly sensitive shear zone, a significant part of which was already impacted by the cave-in. Any further intervention may aggravate the situation, officials said. Additionally, the tunnel top is part of a tiger reserve, a wildlife sanctuary, and protected forests. In light of the above restrictions, the tunnel boring technology was considered for the SLBC works, instead of the conventional drill and blast method. However, the safety outlets were missing.

Missing Safety Niches

Tunnel boring technology comes with its own disadvantages. It cannot provide escape routes or small recesses, also known as niches, built into the tunnel wall. These niches are required every 400 to 500 metres to meet emergencies and to serve as safe havens for the workers in such circumstances. Unfortunately, they are missing in the tunnel being built with a 9.2-metre radius.

The only viable option left is to access the trapped workers through the tunnels by clearing the debris and addressing the water-logging issues that are heavily affecting up to four kilometres of the tunnel and partially affecting up to ten kilometres. The debris inside the tunnel is spread over a half-kilometre distance.

Officials acknowledged that the circular tunnel drilling method has its limitations under these circumstances, making the rescue operations even more challenging. Rescue teams are working tirelessly to expedite the operations and ensure the safety of the trapped workers. The conditions inside the tunnel are being continuously assessed to mitigate further risks and accelerate the progress of the rescue efforts, they added.