SLBC tunnel work advances beyond problematic stretch, set to gain pace

The excavation of Srisailam Left Bank Canal (SLBC) tunnel has moved beyond the major geological hurdle, the stretch where the tunnel caved in claiming the lives of eight engineers, technicians and workers in February last year, paving the way for deployment of additional equipment and improved operational efficiency while maintaining rigorous safety standards.

The decisive breakthrough in the execution of the SLBC tunnel is now expected to gain pace towards the government target of completing it by June 2028, Irrigation Minister N. Uttam Kumar Reddy said at a meeting here on Sunday, where he reviewed the project progress with the engineers, agencies involved in the execution and elected representatives of the areas to be benefited from the project.

The Minister commended the efforts of officials and the workforce engaged in the arduous task and the successful passage of work through the precarious and collapse-prone shear zone. He stated that over 700 metres of tunnel has been excavated since the restart of work in February this year. They were deploying additional drilling equipment and German locomotive to accelerate the operations.

Pressing for the deployment of additional equipment, improved excavation cycles and close safety monitoring, the Minister sought a closely monitored programme to achieve the June 2028 water-delivery target. He instructed the officials and the work agency (contractor) to build on the progress through the difficult geological stretch while safeguarding crews working more than 20 km inside the tunnel from Devarakonda side.

He stated that the project team had reported an advancement of about 700 metres over the preceding five to six months, comprising approximately 450 metres from the outlet (Devarakonda side) and 250 metres from the inlet (Srisailam side). It included a carefully negotiated passage through the major shear zone, overcoming formidable geological, technical and logistical challenges.

The 43.968-km main tunnel was nearly 79% complete now with about 9.1 km of excavation remaining. Col. Parikshit Mehra, an Indian Army tunnel expert spearheading the tunnel operations, explained that excavation at the inlet had deliberately been slowed during the initial months because of the weak ground, rock bursts and the need to prevent another accident.

The diversion around the point where the tunnel-boring machine was stuck had taken the working face through particularly poor geological conditions. To negotiate the unstable stretch, the team installed 140-mm seamless pipes to form an umbrella canopy, providing protective support ahead of excavation, he explained and added that reinforced ribs, staged excavation, probe drilling and additional support measures helped control risks as work advanced.

The Minister said hauling excavated material for distances up to 21 km remained a major constraint. When removal fell behind, excavated material accumulated inside the tunnel, eventually forcing work at the face to stop until the backlog was cleared. Breakthrough in Tunnel 1 could be achieved by May–June 2028 and sprayed lining was being undertaken alongside excavation. The lining work of 7.1 km Tunnel 2 had also resumed after a prolonged interruption, he stated.