East-West Metro borer resumes work after 5-day break

KOLKATA: East-West Metro’s

tunnel boring machine

(

TBM

)

Chandi

started burrowing on Friday after a five-day break. The machine building the west-bound corridor between Esplanade and Sealdah now enters the premises of the 114-year-old Kolkata Municipal Corporation (KMC) headquarters.


Chandi had stalled around 4m from the KMC headquarters on 5, SN Banerjee Road at 6pm last Saturday. It had been digging non-stop since March 26, burrowing 200m from the SN Banerjee Road-JL Nehru Road crossing. The machine needed to be in “static motion” while the single track laid to run the muck car was converted to double tracks inside the tunnel some 25m below.

Keeping the TBM, which weighs around 450 metric tonnes, “stalled” yet “moving” is a challenge and demands hectic technological activity to prevent subsidence. All this time, only one man-rider (technical name for a muck car) was being used to offload the excavated soil.

A second could be used only from Friday, thus increasing the TBM’s burrowing speed courtesy faster muck disposal.

Chandi was supposed to restart on Thursday, but was delayed for 24 hours and could begin only around 11am on Friday. Engineers of Kolkata Metro Rail Corporation (KMRC), which is implementing the 16.6km

Howrah

Maidan-Sector V Metro link, said the TBM could now build 12 rings or 18m a day instead of 8 rings or 12m a day. A single man-rider disposes 50 cubic metres of muck generated during a day’s burrowing.

“Now that two man-riders are being deployed, the speed of tunnelling will increase,” an engineer said.

From now on, the TBM is expected to dig non-stop till Sealdah. Over the next five days, Chandi should complete digging the 50m length of the civic headquarters. KMRC has started strengthening the grand entrance of the colonial structure with iron props. “The building is fairly well maintained compared to the wobbly edifices elsewhere on SN Banerjee Road. But the arch at the main entrance on the SN Banerjee Road side is vulnerable. The slightest soil subsidence would harm this key element of the colonial façade,” a KMRC official said.

The 2.45km stretch between Esplanade and Sealdah is the last leg of the underground tunnelling of East-West Metro.