Telangana to launch aerial electromagnetic survey for SLBC tunnel on Monday

Hyderabad, Nov 3 (PTI) The Telangana government has announced that a helicopter-borne Versatile Time-Domain Electromagnetic (VTEM) Plus Magnetic Geophysical Survey will begin on Monday to restart work on the SLBC tunnel project, which was halted after a portion collapsed in February this year, claiming eight lives.

Chief Minister A Revanth Reddy and Irrigation Minister N Uttam Kumar Reddy will oversee the launch of the heli-borne operations in Nagarkurnool district on Monday, an official release said.

Conducted by scientists from the National Geophysical Research Institute (NGRI), the survey involves flying a helicopter along a 200-km stretch with an underslung 24-metre-diameter transmitter loop that emits electromagnetic signals into the ground.

These signals generate eddy currents, whose reflections are captured by a smaller receiver loop. The data will then be processed to map geological formations up to 800-1,000 metres below the surface, the release said.

"This will help identify shear zones or entrapped water bodies along the remaining tunnel alignment, enabling the adoption of suitable excavation methods to ensure safe and sustainable progress," it added.

On February 22, 2025, a massive geological failure caused water, silt, and debris to flood a 2.5-km stretch of the tunnel in Nagarkurnool district, burying a 130-metre-long Tunnel Boring Machine (TBM) and trapping eight workers who lost their lives, the release said.

Following the incident, a high-level technical committee was constituted, which recommended adopting advanced tunnelling methods, including observational techniques and scientific monitoring, to enhance safety and ensure steady progress.

The Telangana Cabinet subsequently approved the proposal, aiming to complete the tunnel works by mid-2028.

Tunnel experts from across the country also advised carrying out a heli-borne electromagnetic survey. Acting on this recommendation, the state government sanctioned the VTEM Plus Magnetic Geophysical Survey to be conducted by NGRI.

Tunnel-1, part of the Srisailam Left Bank Canal, under the Alimineti Madhava Reddy Project (AMRP), is a 43.93 km-long tunnel originating from the left bank of the Srisailam reservoir.

So far, about 13.94 km of the tunnel has been excavated from the Srisailam (inlet) side and 20.4 km from the Devarkonda (outlet) side, leaving around 9.8 km yet to be completed.

The AMRP aims to provide irrigation to 3 lakh acres in the drought-prone Nalgonda district and supply drinking water to fluoride-affected villages by utilising 3 TMC of Krishna river water, the release added. PTI VVK GDK SSK KH ROH