Chief Minister Devendra Fadnavis has been invited to witness the first of the 17 tunnel boring machines (TBMs) cutting through the ground for Metro 3 construction. The TBM is scheduled to be lowered into a launching shaft in Naya Nagar near Dharavi by the end of this month.
“We have already started the process of lowering the machine with the installation of a steel frame called the ‘cradle’ on which the TBM will be assembled together. We will soon be transporting different parts of the machine to the site on 17 trailers. It is a historic moment and we would like to have the CM with us to witness it,” said
S K Gupta, Director (Projects), Mumbai Metro Rail Corporation (MMRC).
The TBM, which is composed of nine major parts, will take 45 days to be set up underground. First, the front and middle shields would be lowered, followed by the cutter, which will be installed outside the shield and will be the first part to touch ground. Fadnavis has been invited to witness the installation of the cutter as it moves forward cutting through the rock and making space behind it for the remaining parts of the TBM. “The entire length of the TBM will be 110 metres and it will cut a tunnel of 5.8m diameter. However, as the other parts are lowered into the shaft, the machine moves forward and once the Reaction Frame is set up at the back of the TBM, it begins to cut through the rock,” Gupta explained.
The TBM will be guided along the proposed alignment by GPS. Each TBM will have 30 people working inside it in a single shift. Besides, six staff members would be needed at the launching shaft and 25-30 people will be working on ground taking care of the supply chain. Of the 17 TBMs to arrive in the city, 10 will be new and the remaining seven will be refurbished ones. The one to be launched soon at Naya Nagar is a new machine made by German manufacturer Herrenknecht. In a day, the TBM is expected to cut through an average of 8-14 metres and will take a year to cover the 2.5-km distance to reach the retrieval shaft at Dadar.
“We have mandated our contractors to use at least one new TBM in every package. If we were to use all new TBMs, it would increase our overall costs. But the refurbished TBMs are as good as new,” said Gupta.
The Colaba-Bandra-SEEPZ Metro will have 11 launching shafts along the alignment at Cuffe Parade, Azad Maidan, Science Museum, Siddhivinayak, Naya Nagar, BKC, Vidyanagari, Sahar Road, Terminal 2, Pali and Marol Naka. After Naya Nagar, the next TBM will be launched at Azad Maidan in October, followed by TBMs at Vidyanagari and Pali in November. The TBM at Cuffe Parade is expected to be launched by February or March next year.