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  • Tbms recovered, Ew well at Bowbazar to be sealed | Kolkata News

Tbms recovered, Ew well at Bowbazar to be sealed | Kolkata News

By on April 5, 2022 0
Calcutta: The last parts of the giant tunnel boring machines (TBM) ordered to build the last leg of the East-West metro have been removed. The executing agency, Kolkata Metro Rail Corporation (KMRC), has now started the process of closing the salvage shaft at Bowbazar where several houses collapsed after a large scale subsidence on August 31, 2019.
The base will be built first and the shaft will be closed afterwards. Leaving a 9m circumference for the metro tunnel, which is 6m in diameter and surrounded by concrete, the process of backfilling 16m to the surface is expected to be slow, an engineer said. “It can take more than three months,” he added. After backfilling, the entire pit will be sealed. KMRC hopes to start construction of houses for the displaced residents by October this year.
TOI had reported in November that the recovery of the Urvi and Chundi TBMs had begun under Durga Pituri Lane – the Bowbazar collapse area. Urvi, as TBM S-616 was named, was dismantled and retired first. Slicing through the damaged TBM-615, Chundi, which had struck an aquifer, was a challenge, especially as its 9m-wide front shield was covered in concrete that was poured to plug the water leak. Even though the last pieces of the two tunnel boring machines were finally removed last week, tons of concrete and grout still lie inside the collapse zone. All five levels of shoring will need to be dismantled before backfilling can begin. Struts or struts had to be built to reach the tunnel boring machines.
Extracting the TBMs and covering the shaft is the most complex task for KMRC to commission the entire 16 km east-west corridor. The two Sector V tunnels at Howrah Maidan can only be functional once this work is completed. Meanwhile, only the eastbound tunnel is being commissioned to open the Sealdah section of the corridor later this month. The westbound tunnel will begin to receive its final touches now that the tunnel boring machines have been removed. The 75m long machinery emergency gantries have been transported through another shaft at Sealdah Tube Station which can now be closed.
KMRC had started piling works for the 25m deep Bowbazar Intermediate Shaft in August 2020 and completed them in early February. “The 40m x 15m relief shaft was not part of the original tunneling plan. This became urgently needed after the sister machine went missing while drilling the westbound tunnel from the Esplanade to Sealdah,” an engineer said. According to the original plan, the two TBMs were to be picked up from Sealdah after tunneling between Esplanade and Sealdah. But with Chundi damaged, Urvi went as far as Sealdah and turned back to Durga Pituri Lane to complete the drilling.