Because the nation’s first under-river metro prepare operations began in Kolkata, challenge specialists recounted some unexpected challenges confronted throughout its building and the position that two specially-designed German-made tunnel boring machines performed to beat them.
Prime Minister Narendra Modi inaugurated the 4.8-km-long underground stretch on March 6 and industrial operations on it started on March 15. The stretch, a part of the 16.6-km East-West Metro Hall, connects Kolkata with Howrah by way of a tunnel that runs 13 metres under the Hooghly river mattress, or 38 metres under the bottom stage.
Afcons Infrastructure Restricted, which gained the contract for India’s first under-river metro tunnel by way of a global bidding in 2010, mentioned the tunnel boring machines (TBMs) and their backup services, costing about Rs 140 crore and weighing greater than 550 tonnes, had been distinctive in some ways and made an enormous contribution within the building.
“The soil of Kolkata and Howrah may be very treacherous and unpredictable. It’s as a result of the Hooghly river, which is now concentrated to a selected path, had an even bigger presence within the metropolis prior to now so even right this moment there are underground slender channels and aquifers unfold all throughout the town with connection to the river,” Tamal Biswas, Challenge Supervisor, Afcons Infrastructure Restricted, mentioned.
“A staff of specialists studied the soil situations and different components earlier than putting an order to a German agency to fabricate two TBMs with a number of particular options particular to the challenge necessities. We discovered that it was protected to maneuver the TBMs 31 metres to 39 metres underneath the river portion. All through the alignment, the depth of tunnelling is maintained as 16m to 39m.” Moreover, Afcons additionally collaborated with Russian, South African and European engineers who had experience to assemble under-river tunnels.
“Within the preliminary interval, we recruited three to 4 international specialists to know the idea of tunnel as a result of we had been new to this area,” one other knowledgeable related to the challenge mentioned.
Within the regular course of underground tunnelling, the boring machine begins from one underground station and retains boring to the opposite station. Then it’s taken out, serviced correctly and once more positioned all the way down to resume boring as much as the subsequent station.
“In our case, the TBMs had been put down 16 metres under the bottom at Howrah Maidan metro station and it stored transferring underground a distance of 4.8 km masking three stations Howrah (at 30m depth), Mahakaran (at 24m depth) and Esplanade (at 28m depth) with out being taken out as a result of these stations weren’t prepared by that point,” the knowledgeable mentioned.
In accordance with an Afcons official, the TBM had one other particular characteristic permitting it to be transformed right into a submarine in case the river water entered the tunnel and flooded it.
“This is able to have saved the lives of individuals working within the tunnel in addition to defend the tunnel construction already constructed,” the official mentioned.
Afcons officers fondly remembered an engineer whose sudden demise in a street accident earlier than the beginning of the development emotionally motivated them to call the TBMs after his two daughters – Prerna and Rachna.
“We purchased these two TBMs in June 2011 however they had been mendacity idle until 2016 as there was no work occurring because of numerous points and pending finalisation of alignment. In 2015, virtually a 12 months earlier than the development work began, we misplaced one in every of our engineers, Bimal Saha, in a street accident when he was on his method to the workplace,” Biswas mentioned.
“The incident saddened the entire staff. He was a devoted particular person and a really honest official so to pay a tribute to him, we determined to call these two TBMs after his daughters – Prerna and Rachna.” In accordance with Biswas, the TBMs’ particulars had been so distinctive and particular to the East-West Metro Hall that they might not be utilized in some other underground metro tunnel work occurring at a number of cities within the nation with out in depth refurbishment.
“So, we gave them again to the producer as iron scrap. However now we have stored a mannequin in our workplace as a memorabilia,” Biswas mentioned.
A 9.4-km stretch from Salt Lake Sector 5 to Sealdah Junction of the East-West Metro Hall was already operational. Contemplating the continued building between Sealdah and Esplanade Station ( about 2.4 km underground stretch), the competent authority determined to open the 4.8-km underground stretch from Howrah Maidan to Esplanade underneath the river Hooghly as a truncated service.
(This story has not been edited by News18 workers and is printed from a syndicated information company feed – PTI)
