SLBC tunnel costs set to escalate as TBMs abandoned for drill-and-blast techniques
The SLBC tunnel project, originally estimated at Rs 1,925 crore in 2007, has already risen to Rs 4,637 crore and faces further escalation as the government abandons tunnel boring machines (TBMs) for drill-and-blast methods. The government has enlisted the Army, Air Force, and BRO to fast-track the critical 9-km inlet stretch.
Hyderabad: The Srisailam Left Bank Canal (SLBC) tunnel project is poised for a big escalation in costs as the government abandons tunnel boring machines (TBMs) in favor of traditional drill-and-blast techniques for the remaining stretches.
Originally conceptualised in 2007 with an estimated cost of Rs 1,925 crore, the 44-km main tunnel project has already ballooned to a revised estimate of Rs 4,637 crore.
Officials now warn that the change to drill-and-blast method, coupled with a new multidisciplinary intervention strategy, will push the total expenditure well beyond this figure, even though the government has ruled out any scope for escalation.
The move comes after a roof collapse in February 2025 that killed two workers, and six others still missing. It has left the TBM damaged beyond the scope of repair.
In fact, “TBMs are ideal for long tunnels over 10-15 km in stable ground, offering progress of 10-20 meters per day with reduced labour and 20-30% savings on excavation costs,” explained a senior irrigation department official.
“But the unstable rock, shear zones at 300m depth, and seepage from the nearby Mallala Theertham waterfall made it unfeasible. Drill-and-blast, will be slower, with progress at 3-8 meters per day. The government preferred the new method as replacement of the wrecked TBM , which would cost Rs 300-400 crore and take 6-8 months for import and setup.”
The damaged TBM’s cutter head remains buried inside the inlet tunnel, with recovery efforts described by experts as “technically complex and expensive.” Instead, the viable option appeared to be the drill-and-blast method.
Modern controlled blasting may help minimize vibrations. To accelerate progress on the critical 9-km unfinished stretch, the government is enlisting a “multidisciplinary approach” involving the Indian Army, Air Force, and Border Roads Organisation (BRO).
This collaboration aims to tackle persistent challenges like seepage, contractor disputes—particularly with insolvent Jaypee Associates—and the dense forest’s logistical hurdles.
“We’re drawing on military expertise for precision engineering in hostile terrain,” the official added. “This could fast-track the inlet tunnel’s connection to the Srisailam reservoir, but it will inevitably add to costs.
“Progress has been uneven. Over 20 km of the 24-km outlet tunnel has been excavated and the work on the stretch is largely complete. The 6-km inlet stretch, vital for water intake, remains stalled”, he explained.
When the work was resumed in February 2025 after a long gap, the target was to drill 175 meters per month to meet a January 2028 deadline.
However, the cabinet’s ambitious new goal of December 2026 or January 2027 appears optimistic amid funding shortfalls and technical setbacks. Officials caution that further geological surprises cannot be ruled out.
The department is yet to quantify the additional costs from the switch over to drill and blast and military involvement, but preliminary assessments suggest overruns could exceed 20% of the current estimate, he stressed.
