Hyderabad: Even agencies involved in the rescue efforts at the Srisailam Left Bank Canal (SLBC) tunnel collapse incident near Domalapenta in Nagarkurnool district assured that it would be done; a a retired scientist from the Geological Survey of India (GSI) said that procedural challenges, coupled with the failure to locate the shear zones (weak spots), which are the fault-lines in the terrain where the tunnel was being built has caused the incident.
The scientist also pointed out that that until ten years ago, the GSI used to give technical appraisal for all such projects, which was then discontinued, as almost all the contracting firms were now having their own geological wings comprising experts.
Telangana chief minister A Revanth Reddy, who reviewed the progress of the rescue efforts to recover the trapped bodies of eight workers inside the Srisailam Left Bank Canal (SLBC) tunnel near Domalapenta in Nagarkurnool district on Sunday, March 2, urged the agencies involved in the rescue efforts, to document the entire effort on a day-by-day basis.
Terming such an incident as ‘unique,” he felt that the documentation of the rescue efforts and a study of the geological aspects in the area, could act as a case study for the future.
According to a retired scientist of Geological Survey of India (GSI), who preferred to remain anonymous, the SLBC tunnel collapse area which falls under the Amrabad Tiger Reserve (ATR) inside the Nallamala forest, has its crust formed mostly of Srisailam quartzite and granite.
The scientist who headed the GSI for a period, notes that though the rock inside the Nallamala’s crust is structurally competent. There could be some shear zones in the 12 km-long tunnel that was yet to be dug out of the total 44 km SLBC tunnel, he told Siasat.com.
“In these weak spots, highly crumbled stone will be there. The weak point, coupled with the built-up pressure of water which seeped through the earth’s crust and entered the tunnel in massive quantities, could have caused the incident,” the scientist opined about the SLBC tunnel collapse.
Observing that the earth’s crust in the Nallamala forests was certainly more stable than the one in the Himalayas where such incidents could be anticipated more, the scientist said that three of such shear zones were believed to be there in the 12 km stretch of the tunnel passing through the ATR.
He pointed out that even during the construction of the Nagarjunasagar project, such a shear zone was found at its mid-point, where the rectification of the construction works was done by grouting with cement.
“In that project it had an open access, unlike the situation in the SLBC tunnel. I’m sure that pilot holes were dug before the tunnel boring machine entered the SLBC tunnel,” the scientist stated. He observed that the shape of the tunnel itself would act as a support to prevent the collapse in usual circumstances.
The scientist, however, points out that in similar projects initiated by the Centre, such technical appraisals and reports from GSI and other agencies are taken from time-to-time before and during the progress of the construction.
“If the SLBC tunnel project that was initiated more than 20 years ago had continued without any halt during the BRS government, such structural issue may not have happened. Whether it was a human error, negligence, or a procedural issue, unless one looks at the detailed project report of the project, it will be difficult to understand accurately what caused the water to enter the tunnel in such massive quantities,” he added.
Meanwhile, reports have been speculating about heavy flow in Mallela Teertham and Thirumalapur Vagu (local stream) causing the springing up of water in such unexpected quantities inside the tunnel.
| Posted by Vivek Bhoomi | 
