Second borer starts work under SNB

KOLKATA: East-West Metro’s tunnelling for the east-bound track along SN Banerjee Road began on Saturday with the

tunnel boring machine

(

TBM

)

Urvi

starting its journey. Urvi’s twin, Chandi, is building the west-bound tunnel across the road and is currently digging 25m below the 114-year-old KMC headquarters on 5, SN Banerjee Road.

While Chandi has negotiated seven wobbly structures on the western side of SN Banerjee Road, Urvi has the iconic Metropolitan Building to contend with, even though it is digging 3m away from the edifice and the structure’s condition is good. “There was no need to evacuate this building because it’s condition is fairly good,” said an engineer involved in the project.

Three days from now, Urvi will pass the “extremely critical” building where heritage photographic studio Bourne & Shepherd operated from, and then some other very unsafe structures, before passing under Elite Cinema. Later, the TBM will pass BC Roy’s home, another of the many Grade 1 heritage structures that fall on the stretch.

The two TBMs were lowered into the earth to build a 2.4km tunnel from Esplanade to Sealdah. This is the last leg of tunnelling of the 16.5km

Howrah

Maidan-Sector V line. The TBMs must maintain a minimum of 50m distance from each other to prevent ground settlement.

Both TBMs were on a month’s hiatus at the Jawaharlal Nehru Road-SN Banerjee Road crossing before going full throttle under SN Banerjee Road. The break was needed to assemble the entire 75m length of the giant borers.

This leg of East-West Metro’s tunnelling has revealed this interesting “transitional” phase in the journey undertaken by TBMs Chandi and Urvi. Till this point, the TBMs were on their “initial drive”, when the main body dug 80m to make room for the back-up TBMs.

Tunnelling for Urvi has been slow this far. It is only after assembly that the TBM’s drive will gain momentum. “Thanks to the delay in acquiring land, an expansive launching shaft couldn’t be built at Esplanade. The launching shaft was around 10 metres, only big enough to accommodate the length of the TBMs’ main parts. The backup parts were kept above the ground and the machines’ journeys were split into “initial” and “main” drives,” the engineer said.

Coincidentally, even though their schedule couldn’t match perfectly, Urvi’s launching and commissioning has been 24 days after Chandi, which started digging through SN Banerjee Road on March 26. Urvi was launched from the Esplanade shaft precisely 24 days after Chandi’s start on January 26.