The National Geophysical Research Institute’s (NGRI) Multipurpose Time-Domain Electromagnetic (VTEM) survey in Telangana’s Nallamalla forest range, where the Srisailam Left Bank Canal (SLBC) tunnel is under construction, has yielded important information about the geographical fault lines in the area, people said on Monday.
On February 22, 2025, construction was abandoned after a section of the tunnel collapsed, killing eight people, including two project engineers. (PTI)NGRI scientists on Sunday presented the survey reports to State Irrigation Minister N Uttam Kumar Reddy at a high-level review meeting held to discuss resuming construction of the tunnel, which was abandoned after it collapsed on February 22, 2025, killing eight people, including two project engineers.
“The results are encouraging, providing valuable geological information about the shear zones present in the tunnel area. The report will help engineers to pre-identify any potentially hostile geological zones and assess the required tunnel support system,” said an official familiar with the matter.
The airborne VTEM survey, developed by Canadian firm, Geotech, was launched on November 3, 2025 by Chief Minister A Revanth Reddy at Mannevaripalli village in Achampet block. The technology uses a dipole transmitter and receiver combination to measure secondary magnetic fields generated by conductive material in the Earth to map geophysical features. A large transmitter loop suspended 100-150 feet below a helicopter emits electromagnetic pulses into the ground, while sensors record reflections that reveal variations in rock formations, water flow, and mineral composition. The technology can map subsurface geological formations down to a depth of 1,000 meters.
“The combination of aerial accuracy and scientific analysis will give a complete picture of the surface conditions and ensure the safety of future tunnelling,” NDMC scientists are reported to have told the irrigation minister.
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Reddy called for safety protocols in the SLBC tunnel project and round-the-clock operations to focus on immediate assembly and deployment of equipment.
“He directed that the rest of the tunnel works will be executed based on advanced tunneling techniques and monitoring procedures using scientific methods, continuous monitoring and ensuring adherence to international best safety practices,” an official statement from the minister’s office said.
Reddy also announced the creation of an exclusive SLBC department headed by a chief engineer to speed up tunnel construction. He directed that an Independent Supervision Consultant (ISC) be appointed to assist the Chief Engineer in ensuring safety, quality and design compliance during construction.
“The dedicated planning team will monitor the progress on a daily and weekly basis, while tunnel safety supervisors from Singareni Collieries Company Limited (SCCL) will be deployed on site. The minister has ordered formation of special geotechnical and geological teams to carry out daily assessment of ground behavior and stability of the tunnel, real-time statement and real-time statement risk assessment,” the decision said.
Tunnel project, a lump sum price ₹4,600 crore, aims to irrigate 400,000 acres of land in the erstwhile combined Nalgonda district as well as divert Krishna river water from the Srisailam reservoir to provide drinking water to 516 villages.
At the time of the accident last year, a 20.5 km stretch from Debarkonda and another 14 km from the Domalapenta creek end were completed.
