First Month After Work Starts To Be Challenging
World record awaits SLBC tunnel
HYDERABAD: The resumption of work on the Srisailam Left Bank Canal (SLBC) tunnel, on the cards sometime soon, is expected to be a steep learning curve for all those involved with the decision to go ahead with the tunneling using the ‘drill and blast’ method, especially as engineers will need to ensure quick evacuation of toxic fumes from the blasts and dust.
“There will be challenges, and the first one month after resumption of work will be a steep learning curve on blast design, and all other aspects of tunneling,” a source familiar with the planning of work for restarting of work.
Once completed, Telangana will have the longest tunnel in the world to be built without intermediate ducts, which are typically dug either for evacuation of tunnelling muck and for ventilation. The SLBC tunnel, once completed, will be 43.3 km long, longer than the 37-km Wordsmith mine tunnel in North Yorkshire, UK, being dug using a tunnel boring machine (TBMs).
Though the SLBC tunnel too used two TBMs, one from the outlet side in Nalgonda district, and the other from the inlet side near the Srisailam dam in Nagarkurnool district, work was halted in the inlet section after the roof collapse accident this February which resulted in the death of eight workers and in the destruction of the machine.
The second TBM that was being used from the outlet section of the tunnel, had been in a state of disrepair and it is now being dismantled and removed after the government decided based on expert advice to stop using the machines given the uncertainties over the geology of the tunnel alignment and potential for collapses like the one that occurred in February.
“One of the biggest challenges when work resumes inside the SLBC tunnel, will be defuming the work face — where holes will be drilled into the rock which will then be blasted using explosives. There are now much safer explosives which unlike the existing traditional explosives, break the rock safely using shockwaves from the explosion and emit lesser amount of toxic gases. Once that is done, then the next one would be to pulverize the broken rock and its removal,” the source said.
To keep the air safe for workers, in addition to the existing pumping of cool fresh air from outside into the tunnel, a moving system that can evacuate the dust, and fumes from the blast face will also be put in place, the source explained.
A senior irrigation department official said all aspects of the work that needs to be done are being gone over in detail to ensure a safe working environment inside the tunnel. “Yes there are challenges, and we are moving ahead very carefully. All the required equipment and machinery for safe progress will be in place. Once the aerial survey is completed, then we will also have full data on the rock structure along the tunnel alignment that will help in safe tunneling and completion of the project,” the official said.