Hyderabad:The Srisailam Left Bank Canal (SLBC) tunnel, work on which is expected to resume sometime soon, is likely to have a different design for the section that is still to be excavated. The government will now use the drill and blast method, replacing the tunnel boring machines (TBM) used earlier.
Also, though the government has said that it is determined to put the project to work from December 2027, this deadline may have to be pushed back further. One estimate is that the work may be completed only by the end of June 2028.
According to sources in the irrigation department, the contractor could be given this additional time in view of the challenges, some of them associated with the change in the tunnel design.
Work on the 43.93-km long SLBC tunnel was stopped after the February 11 roof collapse this year in which eight workers were killed in the inlet section near the Srisailam dam's reservoir in Nagarkurnool district. The accident also saw the complete destruction of the TBM.
Work inside the outlet section, at the other end of the tunnel, in Nalgonda district, had been at a standstill well before the February accident as the second TBM had developed technical issues needing repairs. According to sources, since these were taking time, some parts from it were cannibalised for use in the TBM that was working in the inlet section till the day of the accident.
While the TBMs have so far dug a circular structure, the 'advanced tunneling methods' to be adopted when work resumes will see the rest of the 9.5 km section in the shape of a horseshoe. According to the sources, in addition to challenges of evacuating fumes from explosives to be used for the drill and blast method, and the associated dust from the blasts and the subsequent pulverisation of the rock pieces, removal and disposal of the excavated muck are expected to pose fresh challenges as conveyor transport would not be feasible with the horse-shoe tunnel section replacing the existing circular section.
It was also learnt that the government had made it clear to the contractor, Jaiprakash Associates, that there would be no further price escalation and the project will have to be completed with the Rs 1,157.42-crore balance available from the last revised estimate of Rs 4,637.75 crore.
Meanwhile, work is yet to begin on building the head regulator at the tunnel's inlet starting point on the foreshore of the Srisailam reservoir. The head regulator -- that functions like a gate -- is a critical component of the project as it controls the flow of water into the tunnel, and regulates the volumes. Keeping all these in view, it is learnt that the company is likely to be given an extension of time if required till end of June 2028.