Months after roof collapse, Telangana tunnel project remains an uphill task

Nearly two-and-a-half months after the collapse of the roof of Srisailam Left Bank Canal tunnel at Domalapenta in Telangana’s Nagarkurnool district, the state government is struggling to find an alternative solution to complete the project which has become a challenging task, officials familiar with the matter said.

The ₹4,600 crore tunnel project aims to transfer Krishna river water from the Srisailam reservoir to provide irrigation to 400,000 acres in the erstwhile combined Nalgonda district besides providing drinking water to 516 villages en route.

Out of the total length of 44 km of the main tunnel, a 20.5 km stretch was completed from Devarakonda end and another 14 km from the inlet end at Domalapenta. Two tunnel boring machines were deployed from either side to expedite the work.

With only a 9.6 km stretch of tunnel being left to be drilled from the inlet side deep in the Nallamala forest range, the tunnel collapsed on February 22 this year, within four days of the commencement of work, trapping eight employees, including two project engineers.

After two months of laborious efforts, rescue teams recovered only two bodies – one that of Gurpreet Singh, the operator of Tunnel Boring Machine (TBM) from Punjab on March 9 and that of project engineer Manoj Kumar from Lucknow on March 25.

According to senior IAS officer Shivashankar Lotheti, who was appointed as a special officer of the rescue mission at SLBC tunnel, only 43 metres of the “critical zone” was left where the bodies of six others might have been trapped. “But it is a risky area to take up the operations,” he said.

How to go about the tunnel project

While recovering the bodies of six other trapped workers continues to be tricky for the rescue teams, state irrigation minister N Uttam Kumar Reddy reiterated that the state government was determined to complete the SLBC tunnel project, come what may. “We cannot abandon the project, as it is a long-standing aspiration of the people of Nalgonda district, and it will turn the region into a fertile green belt,” he told reporters on Sunday.

However, the minister clarified that work on the SLBC has temporarily come to a halt due to an unfortunate accident. “This is only a temporary pause and we shall work out the options on how to complete the project,” he said

He further said that a national-level technical expert committee was formed to facilitate the resumption of the SLBC project. “The construction will proceed based on the recommendations of this expert committee,” he said.

The expert committee, comprising 18 members from various department, has formed a sub-committee with experts, including the Geological Survey of India (GSI), National Geophysical Research Institute (NGRI), National Remote Sensing Centre (NRSC), National Institute of Rock Mechanics (NIRM), Central Institute of Mining and Fuel Research (CIFMR), National Centre for Seismology (NCS), and Col Parikshit Mehra, a tunnel expert from the Border Road Organisation (BRO).

According to a senior official of the irrigation department familiar with the matter, the committee was considering alternative solutions, including a U-shaped rerouting to bypass the collapsed area, using drilling and blasting method (DBM), instead of using tunnel boring machine (TBM).

“There is also an option to drill using a tunnel boring machine from the Devarakonda side, but excavation from the inlet side remains uncertain. The site of the roof collapse is currently deemed unsuitable for resumption of excavation,” the official said.

He said the last 50 metres of the tunnel (referred to as D2 section) pose a significant challenge due to the presence of mud and soil, making removal operations extremely difficult. “This segment falls within a “shear zone” — a geologically unstable area — where any construction activity is considered high-risk,” he said.

The experts committee also discussed the possibility of constructing a vertical shaft from the surface to the tunnel’s end, but this requires approval from the central government as it falls within the Amrabad Tiger Reserve and the government has to take environmental and forest clearance.

Another proposed method involves continuing with drilling and blasting inside the tunnel and transporting excavated debris (soil and rocks) back through the existing 14-kilometre path. Before this, however, experts have recommended drilling boreholes to assess the nature of underground rock layers — a step which also needs central approval.

“Alternatively, ground scanning techniques may be used to assess the strata and plan accordingly. The subcommittee will submit a report recommending the most feasible option among these alternatives,” the official added.