Hyderabad: Chief Minister A Revanth Reddy will inaugurate the Aerial Electromagnetic Survey for the SLBC tunnel on Monday. Revanth Reddy, along with state Irrigation Minister N Uttam Kumar Reddy, will personally monitor the survey and be present during the commencement of the Heli-borne operations.

The survey includes more than 200 km of flying a helicopter with a specialist underslung transmitter 24-metre diameter loop over the tunnel alignment. This apparatus sends electromagnetic signals into the earth to create eddies, which are then reflected and readings are registered on a smaller receiver loop.

These readings are processed to get data about the geology 800–1000 metres below the ground. This will aid the assessment of any shear zones or entrapped water bodies in the balance alignment so that the excavation methodology can be suitably adapted, ensuring safe and sustainable progress.

This tunnel is the longest ever to be excavated without any intermediate access, requiring the best available technologies. The Telangana government has constituted a technical committee with leading tunnel and rock mechanics engineers of India, which has already held six sittings.

On February 22, 2025, a catastrophic geological incident caused massive ingress of water, silt, and rock debris, flooding 2.5 km of the tunnel and burying the 130-meter-long TBM Tragically, eight workers were trapped and lost their lives. Following this event, a high-level technical committee was constituted which recommended adopting advanced tunnelling methods utilising observational techniques and scientific monitoring to enhance safety and ensure sustainable construction progress. The Telangana state cabinet has accepted this proposal of advanced technical methodology with an aim to complete the tunnel works before mid-2028 within the original budget.

Acting on the advice of tunnel experts from across the nation to carry out a Heli-borne Electromagnetic Survey, the Telangana government sanctioned a helicopter-borne VTEM Plus Magnetic Geophysical Survey to be conducted by leading scientists of the National Geophysical Research Institute.

Initiated in 1983, the AMRP aims to provide irrigation across 3 lakh acres in the drought-prone Nalgonda District and supply drinking water to fluoride-affected villages, utilising 3 TMC of Krishna River water. Tunnel 1, part of the SLBCunder the AMRP, is a 43.93 km-long tunnel originating from the left bank of the Srisailam reservoir. Currently, approximately 13.94 km of the tunnel has been excavated, leaving 9.8 km of the tunnel yet to be excavated.