M. Malleswara Rao
HYDERABAD: Yet another tunnel boring machine (TBM), purchased from an American firm for Rs 260 crore, has reached Srisailam to drill the country’s longest tunnel (43.5 km) through Nallamala hills. The tunnel will serve as a canal to take Krishna water to Nalgonda district and possibly to Hyderabad.
Truck drivers performed a feat in moving the 130-metre machine weighing 1,400 tonnes, in pieces from the Chennai Port, negotiating treacherous hairpin curves of the Srisailam ghat road. An action plan has been finalised to assemble the pieces and start drilling a 9.2-metre diameter hole through the hills, a little upstream of the dam.
Lying between 824 and 854 ft of Srisailam reservoir, the tunnel will carry 30 tmcft of water during floods in the Krishna and stabilise the AMR Canal project. The project will make drawals from Nagarjunasagar backwaters by a lift and serve three lakh acres, besides supplying drinking water to hundreds of villages.
Arrangements are on to cut the hills to 824 ft level and create a one-acre artificial open space for introducing the TBM, Y. Abdul Basheer, Chief Engineer, Srisailam, said.
The tunnel lies 300-500 metres below the earth surface as it descends the Srisailam hills and runs through Mahabubnagar district before releasing the waters into a 7.6 tmcft capacity reservoir being constructed in the Dindi valley. From here, a smaller tunnel (7.1 km), which will be manually excavated, will move the waters to the common point of the AMR canal.
Close to the Dindi Reservoir, a TBM has commenced drilling from the other end of the tunnel at Mannavaripalli. According to R. Prabhakar Reddy, Chief Engineer, Mahabubnagar, the two TBMs are expected to drill a half of the tunnel each before being abandoned.
The tunnels and the Dindi reservoir are being taken up at a cost of Rs 2,813 crore. The expenditure on the tunnels alone will be Rs 1,925 crore.