CHENNAI (Metro Rail News): The Chennai Metro Rail Limited (CMRL) is set to commence one of its most complex tunnelling operations in November, as part of the ambitious Phase II expansion project. The forthcoming work involves creating twin tunnels over a 650-metre stretch between Thiruvanmiyur and Indira Nagar, considered among the most technically demanding portions of Corridor 3.
Corridor 3 spans 45.8 km from Madhavaram to SIPCOT via Adyar, including an extensive 26.8 km underground section. Once completed, the line will connect nearly 40 key locations, enhancing connectivity for commuters travelling between Madhavaram and SIPCOT.
At the Thiruvanmiyur station site, excavation has been progressing for several weeks. One tunnel boring machine (TBM) has already been lowered into position, and a second is expected to follow soon. However, engineers have run into unforeseen geological hurdles.
“We anticipated hard rock at Thiruvanmiyur but did not expect such dense, high-quality granite,” a senior CMRL official reported. “While controlled blasting was initially planned, the contractor opted instead for chemical disintegration as a safer and more precise alternative.” as reported by The Hindu.
Excavation has now reached a depth of 22 metres, but the granite formations are expected to slow progress. Normally, a short tunnel stretch such as this could be completed quickly, but officials estimate the work could take up to a year.
The official stated “If the TBM continually drills through hard rock, the cutterhead discs will wear out faster,” the official added. “Multiple cutterhead interventions to replace worn parts may be required for both machines, which will be time-consuming.”
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