Bullet train project: NHSRCL lowers cutterhead of second tunnel boring machine in Navi Mumbai

The National High Speed Rail Corporation Limited (NHSRCL) has said that it has lowered the cutterhead of the second Tunnel Boring Machine (TBM) for the tunnel section of the Mumbai-Ahmedabad bullet train project in Navi Mumbai, officials said on Sunday.

The 13.6 diameter cutterhead, weighing 350 tonnes, was lowered at Sawli near Ghansoli on Saturday, marking the final step in the primary assembly of the TBM's main shield, the NHSRCL stated in a release.

The second TBM will begin tunnelling from Sawli towards Vikhroli in Mumbai. The cutterhead for the first TBM was lowered at Vikhroli last week.

Both machines will now undergo final assembly and commissioning trials before beginning excavation work in the first week of July, the release stated.

According to NHSRCL, the TBMs have been designed to excavate a single tunnel large enough to accommodate both up and down lines of the high-speed rail corridor.

Each cutterhead is equipped with 84 cutter discs, 124 scrapers and 16 bucket lips for excavation and removal of muck during tunnelling operations, it said.

The two slurry-based Mix Shield TBMs weigh 3,080 tonnes and 3,184 tonnes, respectively, and each measures 95.32 metres in length.

The machines comprise several components, including the cutter wheel, main bearing, jaw crusher, erector, main shield, tail shield and four specialised gantries to support tunnelling work, the release said.

The TBMs can operate at a maximum cutterhead speed of four revolutions per minute and achieve an excavation rate of up to 49 mm per minute, while maintaining safety standards, the release said.

The machines are being assembled to build a 16-km section of the 21-km-long Mumbai tunnel. The stretch includes a 7-km undersea tunnel beneath Thane Creek, which will be India's first undersea rail tunnel.

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