A routine water trickle turned into a massive surge, collapsing the SLBC tunnel roof and trapping eight workers deep inside Nallamala hills.
Hyderabad: First there was some minor disturbance but that was nothing unusual. This was at 8 a.m. Then a major geological event occurred.”
“Everyone was asked to leave immediately.”
Some 30 minutes later, after the first event, “there was another major collapse which was even worse.”
This was Glen Mynard, who heads Robbins, an underground construction specialist firm, at the worksite at Domalapenta village from where the Srisailam left bank canal (SLBC) tunnel begins.
When all of this happened, the tunnel boring machine (TBM) on which around 50 workers were positioned, was 14 kilometres inside the Nallamala hills.
During a press conference addressed by irrigation minister N. Uttam Kumar Reddy at the tunnel project contractor Jaiprakash Associates office in Domalapenta, Mynard said, “We heard a loud sound and immediately everybody was told to leave and return to the outside. All those who could leave left.”
“Soon there was a huge rush of water which inundated the machine (tunnel boring machine) to a depth of around 8 metres, and extending to around 120 metres from the tunnel face. Following that we inspected to see for people on the machine, and we could not identify anyone in need. Some 20 minutes later, we left. And 10 minutes after that there was another major collapse that was even worse.”
According to irrigation department officials, what began as an event that was routine at the worksite – water flowing through the rock being drilled through, suddenly turned into a surge with mud and stones falling down.
The flow rose rapidly even as all those at the machine tried to leave and within a short time, a section of the tunnel roof, said to be around 3 metres long, collapsed flooding the spot, with the debris forming a plug and simultaneously sealing a part of the TBM on which eight people were stuck and could not make their way out before the collapse.
