Hyderabad: Work on the bypass tunnel that will sidestep the collapsed section of the SLBC tunnel’s inlet side is progressing and since work was resumed this March, 30 metres have been excavated. The bypass will be a little wider than the original tunnel diameter of 9.2 metres, and will return to the original straight line alignment after crossing the weakened rock zone where the collapse occurred at the 13.9 km mark.
“The bypass, expected to be around 170 metres long, is also expected to be slightly deeper than the gradient of the original tunnel alignment to account for smooth flow of water using gravity. But that is not of concern. All that means is a small section where a pool will be there over which the flowing water will continue to move smoothly once the tunnel goes into action,” a senior irrigation department official said.
The official also acknowledged the four zones of concern as delineated in the NGRI study, and added that since the drill and blast method being used now also has various sensors in place, and the blast system will also provide adequate warning of the rock structure ahead, the coming up to any weak zone will be known before reaching that spot and the pace and system of the work, will be adapted accordingly.
Even if there is water, then it is not such a bad thing as drill and blast produces dust and the seepage could be used for misting to keep the dust levels down which will help in fewer delays in clearing the muck from the blast and moving forward, the official explained.
Meanwhile, sources said that if enough teams can be mobilised by the contractor, then the tunnelling can be completed in 24 to 26 months. This factor is now up to the government which may have to ensure adequate funds are provided to the contractor, not just for the work but also have some redundancies in terms of machinery. This is vital as if there is a breakdown, then standby machinery can be employed to cut potential delays, the sources added.
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