With the holing through at Civil Court underground station seen as a milestone, the joint venture has now completed twin-tube tunnels between the start of the ramp at chainage 10,950 and the NATM section at the start of Civil Court Station (12,600), a total of 1,650m of TBM tunnelling.
TBM ‘Mula’ (S79) is one of three Terratec EPB machines excavating the line; another is the 6.61m-diameter S78 TBM (‘Mutha’) which broke through in September at the 155m NATM scissor crossover at Civil Court Station, having been launched from near the College of Agriculture at the end of 2019. Both machines have excavated in hard rock beneath a densely populated area, complicated by lockdown restrictions which saw a best monthly progress of 301m. Terratec’s field service team was on site to support the effort.
In 2019, Maharashtra Metro Rail Corp (MahaMetro) announced that the JV had won both the twin-tube tunnel packages on the new 16.56km-long north-south metro corridor. The 5km underground section – which runs from the College of Agriculture in Shivajinagar to Swargate and has five stations – is considered the most challenging section of the line, as it passes under the densely populated areas of Kasba Peth, Budhwar Peth and Mandai market.
The Terratec EPBMs have mixed-face, dome-style cutterheads designed to work effectively in the dense basalt that is expected, with pressures up to four bar. As the TBMs progress, they will install 1,400mm by 275mm-thick precast concrete lining segments in a five-plus-key configuration.
The city’s third TBM (S81) is expected to be launched northwards towards Mandai Station early next year with assembly commencing in December 2020.
