TBM S640 Makes a Breakthrough at Kolkata Metro’s Mahakaran Station
On this past Sunday afternoon, tunnel boring machine (TBM) S640 operated by Afcons Infrastructure broke through the northern diaphragm wall of Mahakaran Station on Kolkata Metro’s 16.34 km Line-2, roughly five months after it crossed beneath the Hooghly River and entered into Kolkata’s city limits.
Soil excavation work hasn’t yet commenced at the station, so the Herrenknecht manufactured machine nicknamed Prerna isn’t visible yet to workers. Afcons plans to continue building temporary rings within the station box towards Esplanade, break through the southern diaphragm wall when that gets ready, and later dismantle the tunnel rings built within the station box during excavation. Similar ‘hidden’ TBM breakthroughs, not visible to workers, were recently performed by Afcons at Chennai’s Sir Theagaraya College Station (By S711 and 219-364) as well as locally by TBM S639 at Howrah Station.
Recent image of Mahakaran Station’s site shared on Twitter –
The roughly 2 km journey from Howrah Station to Mahakaran wasn’t an easy one, as the influence zone of the TBM consisted of structurally weak buildings on Brabourne Road (which required temporary evacuation of residents to hotels) and a cluster of heritage monuments like the Writers’ Building, Magen David Synagogue, Beth-El Synagogue, St. Andrew’s Church and Currency Building which required special 24/7 monitoring of soil settlement and grouting injections to strengthen their weak foundations.
With this development, TBM S640 has now come to a temporary halt 19m deep inside the Mahakaran Station’s box. Once the station’s southern diaphragm is ready (located at the bottom-left corner in the image above), it’ll recommence excavation and break through it on the way to Esplanade Station – its final destination. TBM S639 “Rachna” is not too far behind, and is expected to break through the northern diaphragm wall on this Sunday.
For more updates, check out the Kolkata section of The Metro Rail Guy!
Afcons ,great work, length of tunnel?
Roughly 2 kms between Howrah – Mahakaran.
Would have been nice if there was an additional station planned in the middle, somewhere near the Armenian Church along Brabourne Road.
The original alignment had an on-road station along Brabourne road. This had been a severe obstruction to the highly loaded Broabourne road, leading to complete traffic blockade. Hence the relocation of the station.
Really? That’s interesting. What was it called?
This article from 2008 shows Mahakaran as the only station planned between Howrah and Central –
I’m guessing it was planned initially, but got dropped in the detailed project report?
Breakthrough without images! Surprising isn’t it?
I would suggest to check it again with your sources!
Hi, read my post again – this wasn’t a traditional breakthrough visible to workers.
Multiple sources within Afcons, from management to tunnel engineers, have confirmed this development.
Does this mean the average tunnelling speed of 13+ mts a day,a good speed ,taking into account the cluster of heritage buildings along the route .
Is this speed due to soft soil ?
Could we expect similar speed in the section 1 Colaba to CST station in Mumbai ?
S V Phene
Hi, 10-15m of excavation is considered a good day. Anything over that is great. Afcons holds the Indian record for building 39 rings (54.6m) in Chennai.
Some highly rough calculations for the above tunnel –
Duration of 7 months for the entire 2 km Howrah – Mahakaran section – so approx 9.5m/day.
Duration of 5 months for the 1.25 km Hooghly River Banks – Mahakaran section –
so approx 8.3m/day
Can’t guess how the TBMs will perform in Mumbai. Despite regular soil testing, contractors almost always encounter surprises and would have to be extremely careful on that stretch. Piling work for Hutatma Chowk Station has already led to architectural features getting loose and dropping off.
I don’t really understand the technicalities of a hidden breakthrough! If the soil of the station box has not been excavated, then basically the TBM is just continuing through the box, isn’t it? Then how exactly is it a breakthrough, as in literally breaking through a wall? Is it not more appropriate to just say, the TBM has “entered the station”?
It has literally broken through an approximately 1 meter thick concrete wall and entered the station’s site.
Think of the wall as a rectanglular box around the station’s site – roughly 50m wide and 250m long. If they don’t build it first and instead begin excavation work, then the surrounding soil will collapse into the site.
How do they build a D-wall before excavation of soil?
This post has some images and a video –
D-wall always build before excavation. Otherwise soil will collapse.
Ok! Got it somewhat now! Thanks!
Ian happy project is fast completed at work
how you manage to get such minute updates regarding the metro construction?
well, I rode the Kolkata metro last time in 2005 beside Delhi Red Line and those days it was the only metro in the country… Have some good and dark memories of adolescence in those rides . Keep it up, I’ll be revisiting !
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