SLBC Tunnel Work Set To Resume After Months-Long Halt

Mahbubnagar (Telangana): Preparations are underway to resume excavation work on the Srisailam Left Bank Canal (SLBC), which had come to a halt after an accident at the Domalapenta inlet in February. After months of uncertainty, officials have now decided to restart the project using a new excavation method, moving away from the Tunnel Boring Machine (TBM) approach that was earlier employed.

A Difficult Stretch

The most challenging section lies about 13.95 km from the Domalapenta inlet, the site of the accident. A recent heliborne electromagnetic survey has indicated the presence of surface water flow along the tunnel route, along with complex tectonic formations, making excavation risky. To tackle these conditions, authorities are working out a revised strategy. The renewed work will be carried out under the supervision of Army officers Harpal Singh and Parikshit Mehra, both of whom have prior experience in tunnel construction.

Rerouting The Excavation

Officials have ruled out excavation at the accident site itself due to the presence of a shear zone near the inlet. That stretch has been sealed off, and part of the TBM remains stranded there. Instead, a new route will be taken, starting about 100 metres behind the 13.95 km point on the left side. This alternative alignment will later reconnect with the main tunnel beyond the accident zone.

The total length of the SLBC tunnel is 43.931 km. So far, 13.936 km has been completed from the inlet side and 20.435 km from the outlet side. About 9.533 km of excavation is still pending, and officials are aiming to finish the entire project by December 2027.

Focus On Environmental Safety

The remaining excavation will be carried out using the Advanced Technology Method (ATM). While similar to drilling and blasting, this method involves silent blasting, low vibrations, and strict control of smoke and dust. Officials say these measures are intended to minimise any impact on the Nallamala forests, the surrounding environment, and wildlife. Plans are also in place for the safe transport and disposal of excavated soil, rocks, and debris.

Survey Findings Awaited

The full findings of the heliborne survey, conducted under the supervision of the National Geophysical Research Institute (NGRI), are expected within the next 15 days. Once the data is available, experts and senior officials will identify hazardous shear zones and finalise the approach for working through them.

Meanwhile, the TBM stationed at the Mannevaripalli outlet side is being completely dismantled, with its equipment gradually removed. Officials have also decided that future payments to the contractor will be made through a joint account operated by the Irrigation Department’s executive engineer and a representative of the contracting firm, to ensure closer oversight.