TBM drives under old town Mumbai 29 Aug 2019

Excavation of the 3.8km southbound link between Chhatrapati Shivaji terminal and Mumbai central station on Mumbai Metro Line 3 has been completed on a route that required the TBM bore delicately under some of the oldest buildings in Mumbai. Following the breakthrough of the 6.7m diameter Terratec TBM, the section, UCG-02, becomes the first of seven contract packages to be completed. When finished, Line 3 will be the first underground metro in the city and will connect Cuffe Parade business district in the south to the Santacruz Electronics Export Processing Zone in the north, with 26 underground and one at-grade stations (Fig 1).

UCG-02 is the first full section to be completed

With production rates of up to 24m/day, the production record for the project, the machine was driven via NATM-excavated station boxes at Kalbadevi, Girgaon and Grant Road, at an average depth of 20m, through basalt, breccia, and tuff, as well as reclaimed sand with negligible settlement. Excavation was completed on schedule, despite challenges that included proximity to the ocean, boring through reclaimed land, and congested working areas, as well as mining beneath some of the oldest parts of the city.

“Most of the tunnel alignment is under the oldest and most densely populated area of south Mumbai with many dilapidated residential buildings. The performance of the dual-mode TBM in this geology was highly satisfactory and we now look forward to the similarly successful completion of the second TBM,” said Ravi Ranjan Kumar, Chief Project Manager for Mumbai Metro.

Fig 1. The first line to go underground in Mumbai

The machine is one of two new Terratec dual-mode TBMs being used on UGC-02, which was awarded to the Hindustan Construction Company-Moscow Metrostroy Joint Venture in July 2016. Five other Terratec TBMs are also working on the route, so far completing 65% of the 22.6km allocated to them.

The single shield TBMs are equipped to operate in either open or closed mode and have robust cutterheads, mounted with heavy-duty 17in disc cutters, that are interchangeable with ripper tools and feature large bucket openings to provide a 10% opening ratio. The machines also include 2,000kW variable frequency drives that allow the cutterheads to bore efficiently in harder rock zones, at maximum speeds of 7rpm, as well as delivering of 8,500kNm of torque to cope with more fractured zones of ground.