Tunnelling gets underway on Bangalore Metro

Tunnelling was launched last week on Bangalore’s east-west metro line. An official launching ceremony was held at the Majestic Station work site in the centre of Bangalore that contains the TBM launch shaft and will later form the interchange station for the east-west and north-south metro lines.

Launching the TBM is a momentous achievement as it is the first to be used a Southern Indian state and, according to Karnataka Chief Minister Shri Yeddyurappa, it is the first slurry TBM to be used in the country. Taiwanese contractor Continental Engineering Corporation (CEC) is carrying out the tunnelling works and Indian contractor Soma is excavating the stations. The twin bore tunnels will have an internal diameter of 5.6m and will be lined with precast segments manufactured by Ya Li, part of Far Eastern Group.

The 6.44m diameter Hitachi Zosen TBM called Helen is expected to begin boring in the next 10 days and will launch eastwards on an approximate 1km drive to Central College Station. The TBM will leap frog over the station and relaunch on the 727m drive to Vidhana Soudha Station. It will be dragged through this station and continue on the 479m drive to Cricket Stadium Station. The TBM will finally be dismantled and relaunched from the west shaft of Majestic Station and complete the 227m drive to City Railway Station.

The tunnels will bore through mixed ground with a granite rock head of up to 300MPa UCS dipping in and out of the face.

Project manager for CEC Russell Brown said the first 140m of the drive would be among the most testing, as the shallow tunnels with an overburden of just 1.5 diameters will pass under fragile buildings. Settlement will be reduced by using a thick slurry developed by Ian Morrisson of Mudtech.

Helen will be followed on its drives by its sister TBM Margarita with a four-week and 50-100m stagger.