Telangana: Chopper-borne VTEM survey on SLBC Tunnel to commence soon

This project, initially conceived in 1983, is designed in such a way that the tunnel would have no intermediate access

Hyderabad: The Telangana Government has granted administrative approval for a Rs. 2.36 crore Helicopter-borne Versatile Time Domain Electromagnetic (VTEM) Survey for the Srisailam Left Bank Canal (SLBC) Tunnel, a critical component of the Alimineti Madhava Reddy (AMR) Project.

The approval order issued by the government also permits the work to be awarded on a nomination basis to the National Geophysical Research Institute (NGRI), Hyderabad, with funds to be released accordingly.

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The SLBC Tunnel Scheme intends to transfer floodwater from the Krishna River at the Srisailam Reservoir to irrigate 4 lakh acres and provide drinking water to 516 villages in the fluoride-affected regions of Nagarkurnool and Nalgonda districts. This project, initially conceived in 1983, is designed in such a way that the tunnel would have no intermediate access.

The tunnel will span 44 km, of which 35 km has already been excavated. The tunnel, located 400 meters below the Amrabad Tiger Reserve, is being constructed using Tunnel Boring Machine (TBM) technology to ensure environmental compliance and structural integrity. The State government has second thoughts about the tunnel boring methods, especially after the February 22, 2025, roof collapse, which has left six of the eight workers untraced at the accident site, while two bodies were recovered.

The tunnel work has to be resumed by avoiding a geologically unstable shear zone. The roof collapse, occurring between chainage 13.88 and 13.9 km, highlighted critical concerns about the tunnel’s structural integrity. Long-term seepage and hard rock formations have been the main challenges to resuming the work. The government has since decided to bypass the fault zone and is exploring an alternative tunnel extension to enhance safety and accessibility, pending environmental clearance due to the tunnel’s location within the Amrabad Tiger Reserve.

The VTEM survey, to be conducted by NGRI, will utilize state-of-the-art helicopter-borne electromagnetic and magnetic technology to assess subsurface conditions and identify geological risks.

The exercise aims to ensure precision in the revised project approach and mitigate further risks. The government targets completion of the remaining 9 km of the tunnel by December 2026.

In a letter issued on July 5, 2025, the Engineer-in-Chief (General), Hyderabad, requested the government’s approval for the survey, citing its necessity to enhance the project’s safety and efficiency. The government, in a subsequent memo, gave in-principle approval for NGRI to undertake the work.

The SLBC project, launched in 2006 with an initial cost of Rs. 520 crore (later escalated to Rs. 4,600 crore), has faced delays due to geological challenges and financial constraints.