KOLKATA: Engineers and workers engaged to burrow the East-West tunnels below Bowbazar and the residents of the area spent a restless Monday. They kept their fingers crossed ahead of TBM Urvi’s entry into the cave-in zone that had suffered subsidence when TBM Chundee had punctured an aquifer on August 31 last year.
Throughout the day, Leonard John Endicott, the Hong Kong-based geotechnical expert who is also the chairman of the expert committee mandated by Calcutta high court to supervise the rest of the East-West Metro tunnelling, checked and rechecked all the safety parameters. Nobody wants the August-31 script rewritten.
While implementing agency Kolkata Metro Rail Corporation (KMRC) is leaving no stone unturned to ensure safety, residents are going through fear psychosis. Ranju Laha is among the 12 evacuated on Sunday, ahead of this crucial phase of tunnelling. “I hope there’s no repeat of the August accident and my house is in one piece,” the 64-year-old resident of 1B Gour De Lane said. The cave-in zone amid the serpentine lanes off Bowbazar starts here and covers Shyakrapara Lane and Durga Pituri Lane, below which Chundee is now lying defunct. Around 700 residents were displaced as their buildings either fell or were damaged.
Out of 4.9km of the twin tunnels, 1.8km was left when the disaster took place in August. Urvi, on Calcutta high court’s order, resumed digging from the Nirmal Chandra Street-Chaintan Sen Lane crossing on February 18. The gigantic borer is moving slowly; it has barely covered 110m so far.
The Metro tunnels turn towards BB Ganguly Street from Nirmal Chandra Street in a steep curve. Urvi is currently on this 400m radius bend starting at the narrow Chaitan Sen Lane. This curve, however, is not as sharp as the other one that the giant borers negotiated below S N Banerjee Road to turn to Nirmal Chandra Street in June last year. The TBM had hit a water pocket after covering 200m of its second curve.
Around 150 old and dilapidated buildings fall on the curve, along the TBM’s influence zone (25m on either side of the tunnel paths). So far, KMRC and ITD ITD-Cementation, contracted to build the twin Esplanade-Sealdah tunnels, have listed 40 unstable buildings for evacuation. Urvi has apparently passed through five of them. Around 75 % of the 150 structures falling on the TBM’s influence zone have been propped up with iron beams, especially after some households claimed that Urvi’s second stint has left fresh cracks in their walls.
The experts are confident that water ingress is most unlikely this time around. “A four-pronged safeguard approach has been taken to arrest water inflow within an hour,” Endicott had told TOI recently. For instance, the TBM is now protected with additional grease supply lines that have been filled with Condat (world- standard greasing). Then there are the German-make Bullflex seals, customized especially for this project where the TBM digs through non-plastic and extremely porous soil. The seal of Urvi’s tail skin brush has been refurbished. Also, additional grout holes and steel plates are now in place to fill the gap between the machine and the rings.
Throughout the day, Leonard John Endicott, the Hong Kong-based geotechnical expert who is also the chairman of the expert committee mandated by Calcutta high court to supervise the rest of the East-West Metro tunnelling, checked and rechecked all the safety parameters. Nobody wants the August-31 script rewritten.
While implementing agency Kolkata Metro Rail Corporation (KMRC) is leaving no stone unturned to ensure safety, residents are going through fear psychosis. Ranju Laha is among the 12 evacuated on Sunday, ahead of this crucial phase of tunnelling. “I hope there’s no repeat of the August accident and my house is in one piece,” the 64-year-old resident of 1B Gour De Lane said. The cave-in zone amid the serpentine lanes off Bowbazar starts here and covers Shyakrapara Lane and Durga Pituri Lane, below which Chundee is now lying defunct. Around 700 residents were displaced as their buildings either fell or were damaged.
Out of 4.9km of the twin tunnels, 1.8km was left when the disaster took place in August. Urvi, on Calcutta high court’s order, resumed digging from the Nirmal Chandra Street-Chaintan Sen Lane crossing on February 18. The gigantic borer is moving slowly; it has barely covered 110m so far.
The Metro tunnels turn towards BB Ganguly Street from Nirmal Chandra Street in a steep curve. Urvi is currently on this 400m radius bend starting at the narrow Chaitan Sen Lane. This curve, however, is not as sharp as the other one that the giant borers negotiated below S N Banerjee Road to turn to Nirmal Chandra Street in June last year. The TBM had hit a water pocket after covering 200m of its second curve.
Around 150 old and dilapidated buildings fall on the curve, along the TBM’s influence zone (25m on either side of the tunnel paths). So far, KMRC and ITD ITD-Cementation, contracted to build the twin Esplanade-Sealdah tunnels, have listed 40 unstable buildings for evacuation. Urvi has apparently passed through five of them. Around 75 % of the 150 structures falling on the TBM’s influence zone have been propped up with iron beams, especially after some households claimed that Urvi’s second stint has left fresh cracks in their walls.
The experts are confident that water ingress is most unlikely this time around. “A four-pronged safeguard approach has been taken to arrest water inflow within an hour,” Endicott had told TOI recently. For instance, the TBM is now protected with additional grease supply lines that have been filled with Condat (world- standard greasing). Then there are the German-make Bullflex seals, customized especially for this project where the TBM digs through non-plastic and extremely porous soil. The seal of Urvi’s tail skin brush has been refurbished. Also, additional grout holes and steel plates are now in place to fill the gap between the machine and the rings.
Get the app