KOLKATA (Metro Rail News): The Kolkata East-West Metro corridor tunnel boring machine (TBM) Chandi started burrowing on April 19, 2019, after a 5 day break.
The TBM machine building the westbound corridor between Esplanade and Sealdah now enters the premises of the 114-year-old Kolkata Municipal Corporation (KMC) headquarters.
The TBM Chandi had stalled around 4m from the KMC headquarters on 5, SN Banerjee Road at 6 pm on 13 . Since March 26, It had been digging non-stop and burrowing 200m from the SN Banerjee Road-JL Nehru Road crossing.
It 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.
Only one man-rider (the technical name for a muck car) was being used to offload the excavated soil all this time. A second could be used only from Friday, thus increasing the TBM’s burrowing speed courtesy faster muck disposal.
TBM Chandi was supposed to restart on April 18, 2019, but was delayed for 24 hours and begin around 11 am on April 19, 2019. 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 of 50 cubic meters of muck generated during a day’s burrowing.
An engineer said that now that two man-riders are being deployed and the speed of tunnelling will increase. Now, 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. KMRC official said that 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 Roadside is vulnerable. The slightest soil subsidence would harm this key element of the colonial façade. The 2.45km stretch between Esplanade and Sealdah is the last leg of the underground tunnelling of East-West Metro.