BENGALURU: In a remarkable comeback, the Tunnel Boring Machine (TBM) Avni has now completed a total of 70 metres along the underground route from Shivajinagar to MG Road. Avni began drilling on August 29, but encountered a hurdle on October 15. While boring 60 feet under the ground, it came across a sinkhole adjacent to the BMTC bus stand bringing all tunnelling operations to a halt.
Three TBMs are presently carrying out drilling works, while a fourth is on standby for the underground corridor work along the Nagawara-Gottigere Line of Metro Phase-II.“Drawing from the experience of KG Road Metro station in Metro Phase-I, a plan was worked out to thoroughly stabilise the ground around to help the machine continue with digging,” a senior official of Bangalore Metro Rail Corporation Limited (BMRCL) told The New Indian Express.
He said, “We pumped water and cement below the ground using special pumps, which went on for 12 days. The soil was allowed to settle down for 24 hours and then the TBM continued drilling. It proceeds very slowly and drills only 3 to 5 metres a day depending on the soil condition.” It was a challenging and meticulous operation as the four-storeyed hostel of Bowring Hospital was the first building under which the TBM had to bore through after the ground was strengthened. “The inmates of the hostel were temporarily relocated till the boring work was completed. There was no problem after that and we managed to drill successfully. The driver (operator) of a TBM is seated 20 metres away, making it impossible to view what is ahead,” he said.
Avni will drill 800 metres before it touches the MG Road Underground Metro station. “We have completed 70 metres and another 730 metres lies ahead. It would take at least five more months for the tunnelling to be completed. After it completes 100 metres, the second TBM Lavi would begin operating along the same direction,” the official said. The other two TBMs, drilling from Cantonment to Shivajinagar are registering good progress. “TBM Urja has completed 100 metres and Vindhya has started drilling operations,” he added.